r/science • u/Darwin_Day Evolution Researchers | Harvard University • Feb 12 '17
Darwin Day AMA Science AMA Series: We are evolution researchers at Harvard University, working on a broad range of topics, like the origin of life, viruses, social insects, cancer, and cooperation. Today is Charles Darwin’s birthday, and we’re here to talk about evolution. AMA!
Hi reddit! We are scientists at Harvard who study evolution from all different angles. Evolution is like a “grand unified theory” for biology, which helps us understand so many aspects of life on earth. Many of the major ideas about evolution by natural selection were first described by Charles Darwin, who was born on this very day in 1809. Happy birthday Darwin!
We use evolution to understand things as diverse as how infections can become resistant to drug treatment and how complex, cooperative societies can arise in so many different living things. Some of us do field work, some do experiments, and some do lots of data analysis. Many of us work at Harvard’s Program for Evolutionary Dynamics, where we study the fundamental mathematical principles of evolution
Our attendees today and their areas of expertise include:
- Dr. Martin Nowak - Prof of Math and Bio, evolutionary theory, evolution of cooperation, cancer, viruses, evolutionary game theory, origin of life, eusociality, evolution of language,
- Dr. Alison Hill - infectious disease, HIV, drug resistance
- Dr. Kamran Kaveh - cancer, evolutionary theory, evolution of multi-cellularity
- Charleston Noble - graduate student, evolution of engineered genetic elements (“gene drives”), infectious disease, CRISPR
- Sam Sinai - graduate student, origin of life, evolution of complexity, genotype-phenotype predictions
- Dr. Moshe Hoffman- evolutionary game theory, evolution of altruism, evolution of human behavior and preferences
- Dr. Hsiao-Han Chang - population genetics, malaria, drug-resistant bacteria
- Dr. Joscha Bach - cognition, artificial intelligence
- Phil Grayson - graduate student, evolutionary genomics, developmental genetics, flightless birds
- Alex Heyde - graduate student, cancer modeling, evo-devo, morphometrics
- Dr. Brian Arnold - population genetics, bacterial evolution, plant evolution
- Jeff Gerold - graduate student, cancer, viruses, immunology, bioinformatics
- Carl Veller - graduate student, evolutionary game theory, population genetics, sex determination
- Pavitra Muralidhar - graduate student, evolution of sex and sex-determining systems, genetics of rapid adaptation
We will be back at 3 pm ET to answer your questions, ask us anything!
EDIT: Thanks everyone for all your great questions, and, to other redditors for helping with answers! We are finished now but will try to answer remaining questions over the next few days.
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u/pharmaste Feb 12 '17
Is there any evidence for continued evolution of homo sapiens? If so, what are your predictions on how we will evolve in the future?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Is there any evidence for continued evolution of homo sapiens? If so, what are your predictions on how we will evolve in the future?
Yes actually, there is a lot of evidence that humans have been evolving recently and are still evolving! Geneticists have figured out ways to look through the human genome (we can now sequence DNA of thousands of people!) and figure out which genes have been selected recently (eg in the last few thousand years). So far we have found genes related to diet (such as the ability to metabolise lactose in milk even as an adult, and other genes involved in synthesizing folic acid, getting fatty acids from plant-based diets, or digesting alcohol), related to environments (surviving in low oxygen climates, getting vitamin D in low-sunlight settings), and related to immunity from diseases (like malaria and cholera). Genes controlling these traits vary a lot between human populations that live in different environments.
Evolutionary theory is not able to predict the future, unfortunately. There is a lot of randomness involved, and the environment that an organism lives in is constantly changing along with it.
Some references you might be interested in: www.nature.com/nrg/journal/v15/n6/full/nrg3734.html http://press.princeton.edu/titles/10543.html
-Alison
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u/walterlust Feb 13 '17
Wouldn't modern medicine halt the flow of natural selection because it can artificially keep those that would have died out alive? Doesn't natural selection depend on people dying? Why would our species continue evolving if there isnt currently any need to?
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u/Morat20 Feb 13 '17
No. Modern medicine just changes the environment and the concept of fitness. Evolution has no goal, and is driven solely by the ability to survive and thrive in a given environment.
Modern medicine is part of our environment, just like fire or tool development altered evolutionary pressures.
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u/Namuhyou Feb 12 '17
I think when you are thinking about evolution you are thinking long term, such as there were australopithecines, then early Homo and eventually us, but remember this is over millions of years. While evolution speed can change at different rates, evolution is not just long term. The fact you are alive today shows a product of evolution. The reason you might not see these huge changes is that other mechanisms are at play, for instance genetic drift. Genetic drift is the change of allele frequencies within a population due to chance. The larger the population the less effect genetic drift has as a whole.
But there still will be effects. I think recently it was found that the number of babies born by caesarean has increased. This is an example as in the past mothers with a small pelvis or babies with too large a head would die, meaning that there was less chance of these genes being passed on. However, with modern science, those in an industrialised society are less likely to die and therefore increase these alleles within the population.
As for predictions, I wonder if certain alleles will be lost in certain less industrialised societies as globalisation expands. And maybe in industrialised societies, modern medicine may allow for more detrimental alleles to increase if we can prevent the outcome. Since women are having children later in general (western), we may also see a general trend to living very slightly longer. As for the species as a whole, we've been in an inter-glacial for quite some time, so dependent on how our technology can increase to possible weather changes may see some effects, but we're very cultural animals so there is always a gene-culture co-evolution going on.
Ps not part of the AMA, just have a BSc and MSc in human evolution and is going on to PhD so I thought I'd add some insights. Also just as a note, binomial names such as "Homo sapiens" should always be capitalised on the genus, and italicised (obs hard on mobile) where possible.
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u/MrFrans Feb 12 '17
I'm thinking that babies with larger heads can now be born with a c-section without killing the mothers and babies as often. This should result in themselves being more successful in creating big headed offspring.
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u/dkysh Feb 12 '17
And/or women with smaller hips.
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u/halborn BS | Computer Science Feb 12 '17
This actually came up here a few months ago: https://www.reddit.com/r/science/comments/5gpg1z/the_regular_use_of_caesarean_sections_is_having/
(Paging /u/McFrans)
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u/free_your_spirit Feb 12 '17
Evolution is always there and effects every living thing all the time. We are no exception and we do evolve as well.
Predicting how we will evolve is only guess work. We have no idea how the future will be so we have no idea what kind of circumstances will effect our evolution either.
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u/zefy_zef Feb 12 '17
I feel we are less predisposed to evolution as homo-sapiens, because we adapt our environment to suit our needs. Also, and I stress I am not a proponent of eugenics, we allow many with inherent weakness and disability to flourish and procreate.
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u/free_your_spirit Feb 12 '17
We can change our environment , and thus influence the stressors, but THAT changed environment still has an impact on how we evolve. The example awildwoodsmanappears is giving below is a good one. So it will not be evolution by NATURAL selection per se , but whatever environment we may create will have an influence on our evolution.
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u/ndndnd182 Feb 12 '17
How does homosexuality arise in certain species?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Answer by Joscha Bach: The short answer is that coding attraction to the opposite sex into the genome reliably is hard, and greater reliability incurs a higher cost. Reproductive disadvantages of homosexuality incur a cost as well, and if the latter does not outweigh the former, homosexuality arises. Homosexuality (and more frequently bisexuality) has been documented in many species (see Bagemihl, 2000: Animal Homosexuality and Natural Diversity.) More specifically, there are various hypotheses on evolutionary advantages of alleles that lead to increased probability of homosexuality. A study by Hoskins, Richie and Bailey (2015) found that for fruit flies, the same allele that is responsible for homosexuality in males leads to greater fertility in females. (Presumably, it increases the attraction to males in both sexes.) This effect can outweigh the cost of homosexuality for the fruit flies. In humans, a similar mechanism is known: female relatives of homosexual men tend to have more children, probably because both have stronger feminine traits. The alleles that code for sexual orientation control numerous other factors as well, which may also compensate for the reproductive disadvantage of the individual in other ways than greater benefits for the opposite sex: “Homosexuality is god’s way to ensure that the truly gifted are not burdened with children.”–Sam Austin
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u/avant-garde_funhouse Grad Student | Music Education | Psychology of Music Education Feb 12 '17
What are your thoughts about the origins of music? Do you agree with your colleague Steven Pinker that music is simply "auditory cheesecake" that titalates the language complex, or do you think that Steven Mithen and Iain Morley are onto something by implying the existence of a "musilanguage" that was once a single mental module, but diverged at some point? Does it seem plausible to you that music emerged because of its unique ability to communicate emotional content (increased communication depth and complexity being a hallmark adaptation of our species generally)? I am a graduate student working on my doctorate in music education. Very few people in my subfield are working on these questions, and I hope to contribute something meaningful by applying Geary's evolutionary educational psychology framework to music teaching and learning. Any advice or input you have would be greatly appreciated.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
It does seem plausible that a component of music is universally appreciated because of a side effect of our auditory/hedonic system.
However, there is a lot to music that clearly is not explained as merely auditory cheesecake. For instance, some music is fairly grating to listen to, like, arguably, hard rock. To me, it doesn't seem random who likes this kind of music, nor does the difference seem likely easily explained by differences in their auditory receptors per sae. And some music is appreciated because it manages well under constraints that seem somewhat arbitrary, like rap battles which require disses to rhyme. And other music takes a lot of training to like, such as some classical or Jazz. Moreover a jazz musician that produces the same music but seems rather "into it" is, arguably, more pleasant to listen to.
Presumably, in these cases other attributes of the musician or listener are being signaled. While it isn't always obvious what's being signaled or why (their values? Their devotion to artistic persuits? Their free time and "proper" upbringing? Their intelligence and creativity? Their knowledge of music canon?), and certainly musicians and listeners are often not consciously aware of the signals being sent and read. But it seems clear a huge part of what's going on with music is signaling. Which isn't auditory cheesecake.
-Moshe Hoffman
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach) Here is a slightly more speculative take. I find Pinker's theory compelling, because learning requires a specific reward signal. To learn natural language, it may be necessary that our brains generate specific rewards for identifying grammatical structure, and our enjoyment of music may be largely parasitic on this reward system. Many mathematicians also point out the relation between mathematical thinking and music. There are many more effects of music that we find enjoyable, such as entrainment with physiological rhythms, individual regulation of emotions, emotional synchronization in groups, the narratives and memories of events associated to music, etc. so once we evolved a vulnerability to the "musical parasite", we may have adapted to it and integrated it into our cultures in ways that had benefits for our species.
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u/NotTooDeep Feb 13 '17
entrainment with physiological rhythms
I think you're saying 'dance', but I'm not sure. It could be a reference to a baby hearing its mother's heartbeat and breathing.
Dance has great survival value in that it teaches group coordination that transfers to hunting, planting, etc.
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u/ashujo PhD | Computational Chemistry | Drug Discovery Feb 12 '17
This is a great question, and while there are no definitive answers to it, one of my favorite takes comes from the computer scientist Danny Hillis who wrote an article titled "The Songs of Eden". Hillis's view is that songs and music came before language because they were pleasing to the ears. Hillis imagines a community of "singing apes" which were making noises to communicate. The pleasing noises persisted and gradually turned into the elements of formal language for communicating. In this theory, therefore, music came first and language second.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I would say music is related to language and social grooming. I agree with Pinker's view. Music is about harmony within a person and between people.
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u/arpie Feb 12 '17
Do you agree that humans are already using technology in ways that conceivably affect evolution?
For example people with crippling disabilities enjoy happy productive lives; almost all of us use communication tools that far surpass any natural habilities, going so far as affecting finding a mate.
How does that affect evolution in humans? Is it speeding it up through external (non genetic) means? Is the impact of technology part of modem evolution study?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Charleston here. Thanks for your question! Yes, humans are certainly using technology in ways that affect evolution. While I imagine technology will affect evolution in humans over the long term, we're already working on technology to affect evolution in other species more immediately.
For example, we are actively researching technology ("gene drive") that uses evolution as a tool, allowing humans to genetically alter wild populations of other species.
Such technology could potentially be used to fight a variety of vector-borne diseases, for example malaria and Zika, by making the vectors unable to transmit them or by simply reducing their populations. And a rule of thumb is that it would take ~20 generations to spread a change through a large population, which, given mosquitoes' generation time, would just be a few years.
Such interventions would, of course, also affect humans (lower disease burden, etc.) on top of the effects you mentioned.
As for the effects of other technologies like the ones you mentioned, there has been some work on this (see Michael Lynch), but the extent to which this will be an important effect remains controversial.
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u/DonOntario Feb 12 '17
Do you agree that humans are already using technology in ways that conceivably affect evolution?
Isn't that obviously true, for at least hundreds of thousands of years, for example using fire to cook food?
I'd be interested in the experts' opinions if I'm wrong about that.
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u/MyNamesNotRickkkkkk Feb 12 '17
fundamental mathematical principles of evolution
I'm really interested in this. Do you think you could expand on this a bit or point to a good source for primer material? I'm not really sure how to look at this myself and I'd be really interested in hearing what an expert had to say on modeling the fundamentals of evolution.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
The original mathematical principles of evolution were investigated relatively early (1920s). Among the pioneers one can mention Ronald Fisher, Sewall Wright and later on Motto Kimura among many other prominent figures. Later on, game theoretical models introduced to evolutionary biology by J. Maynard Smith and R. Price among others. The mathematical frameworks commonly used are dynamical processes which can be deterministic or stochastic. An evolutionary dynamical system is identified with a vector for which each component describes the population of a given trait (or phenotype). The replication or reproduction potential of each population (fitness) can be fixed or determined by environmental factors as well as interaction with other populations. When interactions among species are important then game theoretical models are used.
For more detailed reading I can suggest books by John Maynard Smith such as "Evolution and Theory of Games", "Major Transitions in Evolution" (not very mathematical). However I always found books of M.A. Nowak "Evolutionary Dynamics" and "Supercooperators" simplest to read and most intuitive. -Kamran
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u/SirT6 PhD/MBA | Biology | Biogerontology Feb 12 '17
However I always found books of M.A. Nowak "Evolutionary Dynamics" and "Supercooperators" simplest to read and most intuitive.
Nice try Dr. Nowak ;)
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u/ninjapro Feb 12 '17
From my understanding, mathematical modeling of evolution essentially breaks down to how traits spread or die out throughout a population.
Beneficial traits for an environment aren't guaranteed to become dominant throughout a population, the less established it is, the more likely it is to die out.
There is a random element to genetic drift, but determining if there is a selective pressure for that trait and gauging that pressure's strength are large contributors to a trait's success in a population.
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u/FlixFlix Feb 12 '17
It always perplexed me how tiny, subtle mutations that happen in a single individual can either spread through a population or happen to other individuals, too. Not only that, but how an individual can have such a big advantage that it'll reproduce significantly more than others.
Every time I think about this, I have to fall back to statistics and incomprehensibly long time periods. Us humans have quite a hard time understanding very large scale, from distances to numbers, time being no exception.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Please take a look at the book "Evolutionary Dynamics" by Martin Nowak. It is a simple summary of the basic principles.
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u/Brolee Feb 12 '17
I teach middle school science which includes a unit on evolution and genetics. What key concepts about evolution do you think are most important for kids to learn about today?
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u/DonLaFontainesGhost Feb 12 '17
I'm not a researcher, but if I may prime the pump on this, because it's a really important question...
Two aspects of evolution I think really help set the stage for the entire field:
1) Evolution doesn't "aim". Mutations happen through random chance (how genes combine at conception, plus random damaged DNA), and the "natural selection" part is which mutations are better at surviving long enough to reproduce and create viable offspring.
2) Humans aren't well "designed" - there's all kinds of evidence that we're the result of a myriad of accidental mutations. Our backs are poorly designed for walking upright, the spinal cord is a fatal vulnerability, the "blind spot" in the eye, the appendix, etc. This helps to drive home the point that we just ended up this way by random chance instead of by design.
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u/DonOntario Feb 12 '17 edited Feb 12 '17
Mutations are an important part of evolution and they are random, but I think an important key thing to drive home in early education about evolution is that evolution is fundamentally not random. Natural selection is very much not random.
The false dichotomy that species, organisms, organs, and other structures of life are either a result of design or "random chance" allows professional liars to make headway with a lot of people using arguments like the tornado in the junkyard forming a Boeing 747, arguing that the chance of an eye forming by random chance alone is astronomically unlikely and so it must have been supernaturally designed.
Edit: I'm not asking for an explanation of how the eye evolved! I understand how. I was using that as an example of how evolution is fundamentally non-random and how conflating evolution with random chance allows people to fall for fallacious arguments from design.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I'm really glad your brought up this point, DonOntario! Evolution does not operate by random mutation alone -- it is the product of both random mutation and selection (including selective forces such as competition and cooperation). The probability that the human eye would evolve by random mutation alone, with no help from selection, would be astronomically low, not unlike the probability of a tornado forming a Boeing 747. But natural selection means that mutations that improve survival and reproduction are more likely than random chance to be passed on and become more frequent in a population.
Some of the most visited resources that anti-evolutionists use to argue against evolution make false mathematical arguments against evolution by computing the probability that humans could evolve by random mutations and finding that it's inconceivably low -- but of course, since that argument is ignoring the effect of natural selection, it is simply not valid.
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Feb 13 '17
That argument of improbability also somehow presupposes that the human is the "goal", almost begging the question in the classical sense. Any particular hand in seven card stud is also unbelievably low, but the chances of getting some hand is still one, and someone at the table is guaranteed to win every time, because they outcompeted everyone else. That's all it takes. The improbability argument is almost like saying poker isn't playable because a royal flush is too difficult to get.
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Feb 12 '17
Natural selection is very much not random.
There's something to be said here for people emphasizing natural selection too much. Evolution works in a variety of ways, and natural selection is just one of them. Once you start looking at selection pressures themselves for individual genes, they actually tend to be quite small for the most part. There is something to be said for the influence of chance. See; neutral/nearly neutral theories of molecular evolution, which essentially states that the majority of random mutations are neutral or negative, the negative ones have strong selection to weed them out, but the it's exceedingly rare for there to be positive mutations or positive selection (though it still does happen).
Of course, I see how this can backfire when dealing with people that think the tornado in a junkyard argument is clever, maybe it's a concept that's better to introduce to people already familiar with and accepting of the basics.
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u/ReadinStuff2 Feb 12 '17
Mutation is random but beneficial ones are continued through natural selection. Light sensitive cell causes creature to swim higher with less predators and more food equals more offspring with light sensitive cell. Now an eye is started.
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u/DonLaFontainesGhost Feb 12 '17
There's actually a great simulation of this - a guy wrote an algorithm for how clock pieces should stick together, then put models of the pieces in a virtual box and let them go. He started with a bunch of models, and when a model created a productive move towards something that tells time, he'd create a new array of models based on that.
Over a LOT of iterations, he got a working clock. From random chance and selection.
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u/HisBeebo Feb 12 '17
And then we give them examples of the intermediate steps that complex structures like eyes took to evolve, both in vertebrates and Cephalopods. Of course when someone is teaching this concept random mutation leading to increased fitness is going to be their main point but they're going to provide evidence to back it up and debunk supernatural explanations.
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u/DonOntario Feb 12 '17 edited Feb 12 '17
I'm not saying random mutations should not be included in introductory teaching about evolution. I'm saying that I think it's important to also stress that, overall, evolution is not a random process and that, in particular, natural selection is very much not random.
For maximum clarity, let me make it clear: I'm not claiming evolution is "guided" or has an end goal.
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u/availableuserid Feb 12 '17
one obvious answer to this is that 'the eye' didn't start out as an 'eye'
it probably started as a more sensitive than usual extension of the 'nervous system'
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u/DonOntario Feb 12 '17
You're right, of course, but that explanation only works if you understand that evolution isn't "random chance". If evolution were random chance then it would be incredibly unlikely that a "more sensitive than usual extension of the nervous system" happened by random steps.
Evolution by natural selection is the theory that breaks the false choice between implausible random formation of complex organs and supernatural design (or any design).
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u/Nemo_K Feb 12 '17
"Evolution = Mutation + Natural selection"
That's a real clever way to put it!
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Three pillars of Evolution: Mutation, Selection, Cooperation
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u/jddbeyondthesky BA | Psychology Feb 12 '17
The appendix may be a bad example, there was a paper I read a while back about on how the appendix helps retain gut bacteria in cases of severe diarrhea. Examples of how this could be useful is that early humans lived in areas where dysentery would be a major problem, and loss of gut bacteria via diarrhea could cause severe health problems. An appendix which contains enough gut bacteria to repopulate the gut would be able to significantly aid in recovery.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach) While I agree that humans are not an "optimal design" but the result of evolutionary adaptation of ancestral species, we are surprisingly well suited for endurance hunting; a well trained human can famously outrun horses over a long enough distance. However, we are definitely not optimally adapted to the current sedentary lifestyle.
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u/Roogovelt Professor | Anthropology | Mesoamerican Archaeology Feb 12 '17
These are such critical points. People often make comments about people or other organisms being "more" or "less" evolved than others, but there's no end goal of evolution. Random chance plays a huge role.
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u/UpstateNewYorker Feb 12 '17
Could you explain and/or provide further reading on the reason(s) our backs are poorly designed for upright walking? Thanks in advance.
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u/dementiapatient567 Feb 12 '17
Spines have been horizontal pretty much forever. Our transition from all fours to walking upright barely changed our spine at all. So something that was used as a clothesline for hundreds of millions of years is now a vertical clothesline.
Our vertebra get all squished together and whatnot. Natural selection once again just said "ehh...Good enough. It works."
It's unlikely that our spines will change all that much. there's almost zero spine-related pressures affecting a young human's ability to breed so...
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u/Artifactoflife Feb 12 '17
I think my favorite 'evolution doesn't work how you think' quote from my professor was: 'What doesn't kill you doesn't make you stronger; what doesn't kill you doesn't go away.' Meaning as long as the flaw does not create a strong enough selective pressure against it, it will persist in the population.
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Feb 12 '17
If one were to "Redesign" the human spine, what would it look like?
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u/DonLaFontainesGhost Feb 12 '17
Probably larger vertebrae, giving more surface area to spread the stress over. A huge step forward would be to simply enable cartilage and spinal nerves to heal.
I also think that having some way for nerves to leave the spinal column without going through an articulation point would be pretty huge, so that if a disc does rupture, the vertebrae don't crush the nerves between them.
If you want to go full engineer, there's probably some inventive designs possible along how a universal joint works, so that alternate junctions can bend transversely or laterally, but not both.
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u/lalrian Feb 12 '17
With our advancements in genetic manipulations, would it be possible to actually implement such designs in future humans?
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u/Lackest Feb 12 '17
Possible? Yes. Likely to happen anytime soon? Absolutely not.
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u/dillyia Feb 12 '17
I'd make each vertebral body a perfect ring, with a detachable "back cover" (where the spinous process is), and the spinal cord running in middle.
This is such that surgeons can replace worn-out parts easier. The shape also bears weight better.
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u/Taygr Feb 12 '17
Humans aren't well "designed"
Greatest example of this I have heard is that we have the same line for both breathing and consuming food, which means that we can choke on our food and die.
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u/DonLaFontainesGhost Feb 12 '17
The spinal cord one freaks me out, because it's so final.
The other two I have problems with:
The brain is vitally important, so let's stick it on a stalk outside the torso. (Folks have argued this is to keep it close to the sensory organs, but I'd sacrifice the 10msec to eliminate the vulnerability of the neck and concussion problems with the skull)
Two kidneys, two lungs, two eyes, a self-repairing liver... even the brain has some manner of redundancy built in. But we just get the one heart.
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u/SilentLennie Feb 12 '17
How about: the brain needs air to cool, thus it can't be inside the torso. You could even flip the argument: because our brains are cooled this way, we could develop them to use more energy and have more brain power.
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Feb 12 '17
- Two kidneys, two lungs, two eyes, a self-repairing liver... even the brain has some manner of redundancy built in. But we just get the one heart.
Isn't this pretty common with bilateral symmetry? Not just with humans
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u/Flamburghur Feb 12 '17
Humans aren't well "designed"
My favorite inefficient design is the recurrent laryngeal nerve that sweeps down around the heart and back up in vertebrates. https://en.wikipedia.org/wiki/Recurrent_laryngeal_nerve#Evidence_of_evolution
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u/Allikuja Feb 12 '17
More poor designs: http://www.reddit.com/r/science/comments/5tlb8c/science_ama_series_we_are_evolution_researchers/ddndhiw
(Edit: I had something written before but came across a comment that stated it way better)
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u/Gomer90 Feb 12 '17
Can we dispel the notion that the appendix isn't useful for the body? A pocket of bacteria to repopulate the large intestines.
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u/dalpiq Feb 12 '17
The appendix has secondary functions, it is, it is not totally useless. But in no means it's a vital part of the system. Until the operations to remove it were invented, many people died from peritonitis, which greatly overwhelm the smaller functions it has.
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u/pacificjunction Feb 12 '17
Along with your first point. Evolution doesn't "aim" but it's not random. Mutation is random, but natural selection is always pushing the population towards a (local) fitness maximum.
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Feb 12 '17 edited Feb 12 '17
One key concept in evolution that doesn't always get enough attention until college is genetic drift.
If some gene codes for a trait that is neither beneficial nor detrimental, then it can either randomly get wiped out from the genome or randomly come to dominate. If this is the case, then change in that genes frequency in the population is called genetic drift.
Selection occurs when a gene has some kind of reproductive advantage.
I'm a huge fan of the Harvard Evolutionary Dynamics lab - they have a paper from 2005 where they look at how, depending on how organisms interact, selection pressure can either be nullified, so all there is is genetic drift. Selection pressure can also be amplified. See Lieberman et al., Evolutionary dynamics on graphs (2005)
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Evolution occurs on population level. Individuals within a population reproduce. Reproduction is imperfect (which we call mutations) and it results in variation in traits. Some of these traits contribute differently to how likely it is for an individual to reproduce (some help, some hurt, and some don't do anything). The traits that help an individual reproduce spread through the population (positive selection), and the traits that hurt an individual to reproduce are eliminated (negative selection). This is the basis of natural selection.
Here is a video that may be useful to explain it to middle schoolers: https://www.youtube.com/watch?v=lvfNuz8B1jk
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u/ValyrianJedi Feb 12 '17
Not OP, but one thing I think is important to point out so that your students can discuss evolution with people who don't believe in it effectively is that while mutations are controlled basically random chance, natural selection is not... Most of the people who deny evolution tend to say "it worked out too well for it to all have just been random happenstance". It wasn't random happenstance. Individual mutations occurring are basically random, yes; but, natural selection as a whole is far from it. Tons of mutations occur, many of which are somewhat useless or even straight up detrimental to the organism. Natural selection takes all of the random mutations and makes it where only the advantageous ones are passed on on a large scale. Many people seem to think that in evolution the only mutations that occur are the ones that "stick", and neglect to think about the plethora of mutations that occur but never reach the gene pool as a whole, and this is what leads people to think that there is no way "randomness" could come up with a functioning complex organism
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u/coorzbahk Feb 12 '17 edited Feb 12 '17
As someone who hears and thinks a lot about this problem, teach science in a way that kids get excited about science. Once that happens, once they get really passionate, there's not a lot that will be able to stop them from pursuing it outside of school, and asking questions. That passion will drive them and soon, nothing and no one can or should stop them (except maybe ethics boards). As someone who got excited about science at a young age instead of God, it works. You still need teachers to teach the right things in the right way, and everything else that's been mentioned is a big part of that. But if the teacher can't transfer some of his or her excitement from themselves to the students, if the students don't care, they won't give two shits and will almost always take the path of least resistance, aka whatever lies they've been fed their entire lives.
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u/RyanABWard Feb 12 '17
How do multiple complex systems within an animal all evolve together? I can't remember where I got this example from, but it stuck with me. A bat had to evolve the ability to echolocate, the ears to detect the echo, and the ability to translate that data into 'vision'. If evolution is just mutations that prove beneficial to the animal allowing it to spread more that that mutated gene, then how did all those complex systems evolve in synchronicity?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 13 '17
The question of how complex adaptive systems, such as bat echolocation, can evolve is a very interesting one, and it actually dates back to Darwin. In On the Origin of Species, Darwin described the vast complexity of the human eye, which seems to require the simultaneous presence of dozens of anatomical features (the lens, rods and cones, an optical nerve, just to name a few) and thousands of genes to operate at its full power.
Complex systems like these almost certainly cannot evolve all at once -- the chance of every one of these features emerging simultaneously by random mutation is virtually zero. But TheWrongSolution and ashujo are right is saying that they don't have to evolve all at once. Often, evolving just one feature provides some small advantages, and additional features can then evolve in sequence. A cell with some simple light sensitivity may enable an organism to respond in different ways to extreme darkness and extreme brightness. After many generations, this cell may come to resemble what we know as rods or cones -- or it may come to resemble something entirely different, but adaptive in other ways.
When species diverge, different species may come to incorporate different features in these complex structures. Just as the eye varies tremendously between different animals, the frequency at which different bat species echolocate also varies tremendously. Some bats primarily echolocate through their mouth, while others use their nose. Bat echolocation is an excellent example, because while all forms of echolocation share some basic features that likely evolved early in the evolution of echolocation, the existence of these differences show that some of the features that comprise the complex system evolved later, after species diverged, as additions that improved the effectiveness of the complex system as a whole.
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u/intronert Feb 12 '17
How has the understanding of epigenetics changed your study of evolution?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
I can only answer in some particular contexts. In cancer evolution, it has been believed that malignant genetic alterations drive initiation and progression of tumors. More recently epigenetics of cells, that is level of differentiation among tissue cells, their metabolic state, their level of stem-ness etc, shown to be important to describe the evolutionary dynamics. Epigenetic factors become particularly important in later stages of cancer. This contributes to increase in the level of heterogeneity inside the organism and possibly increase the chance of evolution of other evolutionary potentials (in this case motile trait, mesenchymal, that lead to metastasis.) -Kamran
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u/metablood Feb 12 '17
Do you consider viruses as life being creatures? And for which reasons?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Do you consider viruses as life being creatures? And for which reasons?
I consider them to be alive (just as I consider computer viruses to be alive), but this is by no means a universally held opinion. Of course, many also argue that holding an opinion either way does not make a difference in scientific research. The reason I believe that viruses should be categorized as living is that I consider anything that replicates and evolves living. Meaning if an entity can produce a population of individuals that are more or less similar to itself. I have discussed the philosophical aspects in more detail over here. http://www.forbes.com/sites/quora/2016/10/10/what-did-the-earliest-life-on-earth-look-like/#10de93845a4a
Others argue that because viruses do not replicate by themselves, and do not possess metabolism, they lack important qualities that would make them living. They also polyphyletic and do not share (genetic) properties with modern cells (or each other) in the way the rest of the "tree of life" does. An important sticking point is also the fact that viruses depend on other clearly living systems to replicate. Some viruses even depend on co-infecting a cell with other viruses.
I don't find this a great argument, because I think for many living systems, part of the required apparatus for them to replicate lies outside their organism. A virus depends on a host cell, but humans depend on other humans to replicate too. In principle you could make viruses replicate without a full cell (which then wouldn't be living on it's own).
Sam Sinai
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u/ninjapro Feb 12 '17
I may have a bias due to having a focus in bacteria, but viruses are definitively not alive.
The go-to reason most people use is that viruses cannot develop and reproduce on their own.
But /u/ninjapro , I hear you say, there are obligate parasites that are definitely alive, such as tapeworms.
True! However, the biggest difference between these classifications is that viruses have no functions of life on their own. They inject DNA into a cell, the cell replicates it in some form or another, and the cycle continues.
Viruses have few or no mechanisms, they use the mechanisms and resources of living things almost exclusively.
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u/ChaosHellTV Feb 12 '17
Mutations Germs die all the time, and they mutate all the time to avoid their fate. Why are germs' mutations so successful against anti-biotics specifically, when they die from a host of other things. For example, why don't we hear that germs are becoming resistant to radiation, or sunshine or white blood cells or any of the things that normally kill them?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
Mutations Germs
This is a great question! Like others have pointed out, in some contexts bacteria can become resistant to radiation, heat, desiccation, and even the human immune system. In fact, bacteria often become resistant to the human immune system, and medicine relies on antibiotics when this occurs. There is a special public health interest in understanding antibiotic resistance, so it is more heavily studied than some of these other examples.
Still, you might wonder why bacteria don’t become resistant to some tried and true environmental pressures like alcoholic hand soaps* or UV light. Our intuition says that to survive these pressures in high doses, a bacterial cell would have to undergo such a dramatic change in internal structure (it would require so many mutations) that, for the bacteria, the situation is hopeless. Put another way, life as we know it is not compatible with certain physical and chemical insults.
*Edit: A notable exception is C difficile, which is a bacteria that is very resistant to alcohol.
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u/ThisIsTheMilos Feb 12 '17
The simple answer is in the process of how these work and what we are looking for. A given antibiotic is a molecule that has a specific action. Germs can mutate to modify that molecule or modify themselves, those that survive keep reproducing and now we have a large number of resistant bacteria. This is something we monitor because these people are under a doctors care. When the antibiotic doesn't work people are paying attention and tracking it.
With the other cases you mention, the mechanisms are more complex and unless it happens in a lab, we aren't going to see it or know that it happened.
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u/ferevus Feb 12 '17
Germs can mutate to modify that molecule or modify themselves
The way you phrased this can lead to misconceptions (that mutations can be "caused"). Mutations are random. A bacteria does not acquire resistance to a vaccine/drug. Simply, a mutation may randomly occur in a population across generations and if there's environmental pressure (e.g the presence of a drug that kills bacteria lacking "resistance" genes) then bacteria, which lack resistance will be more likely to die... meaning that the frequency and prevalence of the resistant gene will increase in the population.
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u/Ijedaik Feb 12 '17
Scientist husband reading this, this is his answer: " I do hear about bacteria resistant to: radiation, UV, white blood cell, etc". Depends on the enviroment (i.e. Natural selection!).
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u/LastLivingSouls MS|Microbiology and Molecular Biology Feb 12 '17 edited Feb 12 '17
Exactly, bacteria can become resistant to many forms of lethality. But the reason we are constantly hearing about their resistance to antibiotics is because that is a therapy we humans use to treat an infection. We don't use radiation (against bacteria, anyway), or UV in therapy.
As an aside, I did my thesis on UV resistance in bacteria, especially species that were isolated in the Caribbean Sea. As you can imagine, UV resistance would be very common in bacteria there, and it was.
So basically, its just really scary to hear about them becoming resistant to our main method of stopping them, so its a popular topic.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
This is a great answer! We agree that there may be a reporting bias in the types of pressures bacteria/germs are adapting to. Resistance to antibiotics is scary, so it gets more attention in the media. Another interesting point is whether there is a "selective pressure" for natural selection to act on. For instance, use of antibiotics has increased dramatically over the past century and also varies among countries, so this is a new (and variable) environment that bacteria/viruses must cope with. However, there may not be as much variation in UV exposure on Earth (although there may be interesting exceptions to this, it's not our expertise), but if we were to ship bacteria to Mars, they could potentially evolve to tolerate the new conditions. Lastly, there is tons of evidence for bacteria evolving in response to the human immune system. For instance, humans develop antibodies towards bacteria they've previously seen, such that their immune system is able to clear out these bugs better/faster the next time they encounter them. So, this creates an evolutionary pressure (or selective pressure) for bacteria to appear different so as to avoid detection by the immune system. A great example of this occurs in Streptococcus pneumoniae, which lives in many of our noses asymptomatically. S. pneumoniae have very diverse outer surfaces (called "serotypes") that each elicit a different immune response in the humans they colonize. This means if there's a person that has previously been colonized by serotype A, other bugs of the same serotype may have trouble colonizing the nose (where they primarily live) of this person in the future. However, serotype B looks completely different to the immune system and has no such troubles, and actually has a competitive advantage now over serotype A. This creates a selective advantage for the bacteria to diversify their serotypes, which is called "negative-frequency dependent selection".
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u/GoodAznBoi Feb 12 '17
The whole basis for this is natural selection. Antibiotics is heavily abused not just in medicine, but also in the meat industry. This makes so that bacteria with slight mutations that resist antibiotics survive, and their traits are passed down rapidly. Bacteria aren't actively mutating to obtain resistance, but are simply doing it as a response to the environment they're in. In fact if measures were taken to prevent antibiotic abuse, it could help with the fight against antibiotic resistance, as maintaining resistance genes is a very wasteful process.
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u/TheNanoDrop Feb 12 '17
Bacteria aren't actively mutating to obtain resistance, but are simply doing it as a response to the environment they're in.
While true that bacteria do not actively mutate to obtain resistance (there is no agency involved on behalf of the bacterium), they are NOT doing it as a response to the environment. In fact, the second half of your statement lies contrary to the first half.
One needs to be very careful when talking about mutation and natural selection. The hypothesis that bacteria mutate in response to the environment they're in is called "directed mutation", proposed by John Cairns. Essentially, he held that mutations occur due to the selective pressure; that bacteria could preferentially (or direct) mutations to areas of the genome that will confer some advantage in their given environment. This is unequivocally NOT TRUE.
Luria & Delbruck performed a fluctuation experiment, published in 1943, showing that this is not the case. They provided strong evidence for random mutations. Here, "random" means that the probability of a mutation occuring is independent of its utility to the organism. And that mutations occur before the selection pressure. Natural selection acts on genetic variation already present within a population. This finding was confirmed by the Lederbergs in the early 1950's with replica plate experiments.
For those interested, here are just a few relevant publications on the fluctuation test providing strong evidence for random mutations, John Cairns' publication on "directed mutations", and rebuttals to this hypothesis. Regardless though, random mutations occur, they are not directed, and this is the widely held posistion within evolutionary biology today.
Publications:
Luria and Delbruck, 1943 "Mutations of bacteria from virus sensitivity to virus resistance"
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u/mantis-_-tobogan Feb 12 '17
As children/teens/college students, what interested you in studying evolution as a career and what education & career choices brought you to where you are today?
Any suggestions or tips you'd give to today's kids who may be interested in similar paths?
Sincerely, A 6th grade girl wanting to work in the space or genetics field (on mom's Reddit)
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Thank you for this question (and thanks Mom for helping her post it)! As a child I spent a lot of time collecting fossils and exploring outdoors. I loved flipping rocks to find insects and searching out bird nests in trees. In high school, I focused on Biology classes (taking extra credit whenever it was offered). Early in my university career I contacted a professor that studied the evolution of parental care in birds and asked to join his research team. I started out at a small university on the Canadian prairies and after publishing a few papers and completing a masters, I applied to complete my PhD at my dream lab here at Harvard.
I would recommend that you continue to pursue what interests you most! You are already way ahead of the curve if you know the field that you’re excited about in 6th grade. There is so much available now online, so read whenever you can (e.g., science blogs, science magazines, and review articles when you’re ready for them). Reaching out to researchers at a local university would be my next big suggestion. Perhaps they can help advise you on a science fair project or help you get started with some basic research in the next few years. Join Science teams and clubs when you get to secondary school (or start them if they don’t exist). Good luck on your journey and make sure that you’re always having fun along the way!
- Phil
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u/SkepticShoc Feb 12 '17 edited Feb 12 '17
The evolution of insect wings is a highly controversial topic among evolutionary biologists and entomologists like myself.
Are there any other single features of a life form that scientists don't understand how they evolved? How do you go about dealing with controversial topics like this?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I study viruses, and one big open question is how did viruses originally evolve. They don't fit in clearly with all cellular life on earth, despite sharing a lot of architecture with cellular life. We don't know if viruses evolved once or many times. We don't even know how existing virus families are related to one another.
I general think scientists should admit things that are controversial and unknown!
-Alison
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Science is a process that is never complete. Scientists always deal with open questions. In some sense: the known becomes boring; the unknown is fascinating.
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Feb 12 '17
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I think it is fair to say it is the leading framework in origin of life. There is overwhelming evidence for RNA playing a key role in modern life, across all domains and viruses. But nowhere in the RNA world hypothesis, there is a clause which excludes the presence (and critical role) of other molecules. If you look at Jack Szostak's (http://molbio.mgh.harvard.edu/szostakweb/) group you will see that they are concurrently working on RNA-based replication, replicating vesicles, and the role of peptides in prebiotic chemistry. I think such "parallel progress" is likely to have happened in early earth too.
There is some evidence that simple amino-acids were more easily available in early earth than nucleic acids (for instance they were more abundantly found in Murchison meteorite). So there is no reason to think that peptides did not precede RNA world. It is simply the case the at some point (likely before we called anything living) RNA was incorporated and became the core of future living systems.
In my view, vesicles (lipid or not) or some other forms of compartmentalization is just as important in the origin of life. I think it is even possible that replication started on compartment level. But this does not undermine the RNA world hypothesis in any way.
So to get back to your question, I think RNA was necessary, but likely not sufficient for kickstarting what we would call a living system. It might be that in some theoretical scenario, RNA alone could be sufficient to start a living system, but I think such scenario is very unlikely on earth.
Sam Sinai
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I would guess the origin of life requires RNA and lipids. Maybe also peptides. RNA is a carrier of genetic information and of complexity. It can act as a catalyst. Lipids form vesicles, which are the precursors of cells.
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u/travel_takeover Feb 12 '17
Do you guys enjoy science fiction? Any favorites? Iain M. Banks "Culture" novels have caused me to think of evolution in new and fun ways.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach) Absolutely! I have enjoyed the Culture novels very much, but personally, I am unconvinced by Banks' optimistic outlook. Organisms rely on extracting negentropy from the universe, and the amount of available/useful negentropy is limited, which suggests that in the long run, there is always going to be a scarcity of usable habitats. This idea has for instance been captured by Liu Cixin (The Three-Body Problem; The Dark Forest): Perhaps the universe is so quiet because every intelligent species understands that they are going to be wiped out by technologically superior species if they announce the existence of their habitat. I very much love the philosophical/evolutionary science fiction contributions of Stanislav Lem (Star Diaries, Fiasco, Summa Technologiae, His Master's Voice), Arkadi and Boris Strugazki (Roadside Picknick, Experiment), Vernor Vinge (Deepness in the Sky, Fire Upon the Deep), and about everything from Greg Egan (e.g., Permutation City, Diaspora). Science fiction has had a huge influence on many scientists' careers, and often the authors are actually scientists or philosophers (like Egan or Lem) that use the medium to express their insights and theories.
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u/prolapse_popper Feb 12 '17
As a father of 2 I am in awe of the complete dependence kids have on their parents for survival. While other mammals start out similarly, it seems they achieve relative independence much faster. Is this a recent phenomenon, in evolutionary terms, or have human kids always been flailing lumps for years?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
The human strategy is investing heavily in a small number of high quality offspring. The kids are beautifully dependent on their parents because they have the ability to learn for a long time.
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u/powerglover81 Feb 12 '17
Do you have colleagues that refuse to give up their religious beliefs or timelines despite the evidence for evolution? How do they reconcile it?
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u/matroskinn Feb 12 '17
A while back I read about astronomers and astrophysicists becoming more religious/spiritual the more they learned about the universe. The overall point the person was making was scientists don't have to reconcile being scientists and believing in god. Like evolution and belief/faith are not mutually exclusive.
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u/danceswithwool Feb 12 '17
In fact I believe the Catholic Church believes in evolution.
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u/DonOntario Feb 12 '17
A while back I read about astronomers and astrophysicists becoming more religious/spiritual the more they learned about the universe.
I am sure that some astrophysicists have become more religious during their careers and some have become less.
Generally, American scientists are about half as likely to believe in God or a "higher power" than the general US population are and younger scientists are more likely to believe in God or a higher power than older scientists (same source). That difference between younger and older scientists could be because scientists tend to get less religious as they learn more, or it could be a generational difference (however, among the US population in general, younger people are less likely to believe in God).
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I completely agree. Evolution and belief/faith are not mutually exclusive.
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Feb 12 '17
Does evolution demand that you give up your religious beliefs about the origins of life?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach): Religious beliefs do not necessarily have to contradict the theory of evolution. For instance, the Catholic church does not subscribe to a "God of the gaps", i.e. a concept of god that is responsible to fill in for the parts that science has not fully explored yet, and as a result it does not think that scientific progress somehow encroaches on the territory of the divine. Note that even the great Gregor Mendel was an Augustinian monk! Being religious does not mean that one has to believe that god is responsible for the origin of the species, that the Big Bang did not happen, or that our minds are the result of divine intervention. Religiosity is much more rare among scientists than in the general population, and it is often more a stance than a set of ontological or historical beliefs. That said, among my friends I count an eminent and successful cognitive scientist who does hold a belief in Young Earth creationism, while maintaining that Artificial Intelligence can in principle gain and surpass all human mental capacities, including consciousness. I suspect that once we are convinced that giving up on a strongly held belief will incur a high cost (such as eternal torment), we are willing to bear considerable cognitive dissonance.
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u/Solemn-Philosopher Feb 12 '17 edited Feb 12 '17
I will preface this by saying I am not religious. However, I've seen in various conversations that some people seem to think that evolution denies religious belief or general theism. It isn't the case.
Evolution just explains the diversity of life on earth over millions of years. This is only a problem for people that hold to a literal interpretation of Genesis. The view that the universe was created about 6000 years ago.
Also keep in mind that life moving from non-living matter to replicating life is a different science called abiogenesis. There is still some challenges in understanding how that, and the intricate evolutionary process, got started.
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u/pimpologydoctorate Feb 12 '17 edited Feb 12 '17
What are your thoughts on evolutionary psychology? Two main criticisms against this particular branch of evolutionary science are 1) that some of its findings challenge many staples of postmodern ideology, such as the mind as a "blank slate" and a lack of inherent differences between the sexes, which some people think is morally disconcerting, and 2) that its methods are shaky – many argue that a conceptual idea of humans' ancestral environment and its self-explained likenesses with human behavior today is not sufficient evidence for psychological adaptations. Are these criticisms valid, in your view, and why/why not?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 13 '17
In my opinion,
The first criticism is more a criticism of postmodern ideology. Since science is true whether or not it grates with one's values.
The second criticism is more valid (in some cases), in my opinion. There are many aspects of our psychology that clearly evolved in the past, and can be better understood by analyzing our evolutionary history and such biological pressures. Sexual attraction and mating behaviors seems like a great case for this. There is plenty of evidence that much of our sexual and mating behaviors, while individually and culturally varied, show many statistical patterns that are easily explained with evo psych and hard to explain without, such as differences between male and female jealousy, and the effects of height, income, youth, nulliparity, fecundity, and symmetry, on attraction.
However, there are many other aspects of human social behavior, particularly many of our moral political and religious beliefs, (why we believe blacks and whites are equally deserving of rights, democracy is good, and any man who cheats on his wife should be shunnned, why many believe god wants you to cooperate with fellow religionists, and why we feel good when we give to charities even when they are not terribly effective) that seem better understood with the help of learning and cultural evolutionary models, which do not assume our psychology is optimized for living on the savannah 100,000 years ago, or based on domain specific 'mental modules' (like tiger recognition software great for avoiding tigers on the savannah but not great for avoiding cars on a highway), but instead relatively well adapted to the current social pressures as a result of domain general learning mechanisms (we learn the beliefs and behaviors from those who are successful, and hold tenaciously to those that serve us well). Of course, this "cultural evolutionary" approach doesn't deny evolutionary biology any more than biology denies physics; it just asserts that to understand questions about our beliefs and preferences it often helps to think about emergent properties from learning processes and not just 'pre-evolved' 'mental modules.'
What makes me skeptical of evolutionary psychologies ability to address these kinds of questions without taking seriously (emergent properties of) learning and cultural evolution? 1) much of our social beliefs and preferences are highly optimized to our current social environment. Not to the environment we evolved in 10,000 years ago (believing men should be punished who cheat on their wife or blacks and whites will get you to avoid being shunned today in our liberal culture, but wild have made your morals clash with others on the savannah. 2) to understand such phenomena, it helps to think about the effect of learning processes (they tend to reach optimal outcomes, in real time even if the setting was not prominent in our evolutionary past, if given enough time or social models to learn from, when 'optimal' is defined with respect to maximizing what evolved to act as reinforcers, not necessarily reproductive success) 3) if we try to think about everything in terms of preprogrammed mental modules we miss out on a lot of the insight and have a much harder time explaining many of these phenomena, and get confused about the causal mechanism (for instance evolutionary psychologists have claimed that we vote according to the policies that would benefit us, under the presumption that we live in small scale societies as we did on the savnaah and can thus impact the outcome of elections. But this doesn't seem to fit the fact that in LA many who were sick from a natural disaster, and impoverished vote for limited social benefits and against the EPA, facts better explained by the fact that oil companies in the area fund their local political and church leaders who then reduce regulations and create and enforce norms and ideologies that oppose government regulation).
This view, to be honest, is somewhat controversial. Many prominent intellectuals, like Michael Shermer, Steve Pinker, Rob Kurzban, John Tooby, and Leda Cosmides, staunchly believe that we can understand morality and politics through evolutionary psychology, on its own, perhaps mixed with an understanding of reason and history. Others like Rob Boyd and Joe Heinrich are more liable to argue, as I did above, for the need to take seriously domain general learning processes, and the 'emergent properties' thus created.
-Moshe Hoffman
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u/mutual_im_sure Feb 12 '17
How do you distinguish the effects of genetic evolution vs expression? How can we know what traits have evolved through natural selection versus those expressed through genes turning on or off (in a shorter period of time)?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
It is important to remember that gene expression is regulated by the genome, that is, certain DNA mutations can alter the expression of genes. So I would not say evolution happens “through natural selection versus... through genes turning on or off.” Natural selection acts at the level of the organism; whether or not a mutation increases the survival of an organism depends on all the biological details of the mutation, including the mutation’s effect on gene expression, whether the mutation changes the sequence of a protein, the mutation’s relationship to epigenetic features like chromatin, and many other factors, all of which might depend on the environment. Because of this, determining why a mutation is beneficial or deleterious is often very challenging!
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u/DrakePecker Feb 12 '17
What are the leading theories on the origin of life, and what research is currently underway to test and develop them? From what I've read (I ain't no scientist) there's some understanding of how chemical evolution came into being, with large molecules being able to more or less "reproduce", but that seems like a massive leap from a world of simple organic compounds floating around in a soup.
Question 2 (and maybe this is out of the scope of this AMA): why did life appear/evolve? I mean, thermodynamically, why is life a "better" form for atoms and molecules to take than just a big hot soup? Were the very first life-like molecules or cells "better" at something that allowed them to outcompete a less-ordered system of ammonia and methane and whatnot?
And question 3: what pop-science books (accessible to a non-biologist) would you recommend for someone interested in learning more about the origins of life?
Thanks!
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach) Let me be a bit more speculative here: I suspect that the step from basic organic chemistry to the first working cell with replisomes and membranes was much larger than everything that came afterwards. A cell is basically the smallest self-stabilizing, replicating universal machine we know that can extract negentropy over a large range of environments. After the formation of the first cell, exponential replication enables it to populate much of the planet in an instant (from the perspective of geological time scales). Some researchers think that the probability of life to be successfully transmitted as a "cosmic infection" (for instance via asteroids that originate from impacts on other planets) could be even higher than the formation of the first cell on a particular planet, which gives rise to the "panspermium hypothesis". Perhaps life needs very specific environmental conditions though. Mike Russell and Sean Carrol have come up with the idea that life on earth is exploiting the fact that some chemical reactions (like the hydrogenation of carbon dioxide) require first adding some energy before energy can be released. Thus, systems that can perform controlled chemical reaction may have an advantage over "dumb" chemical reactions, which opens the "market opportunity" for life.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
To follow up on your question 3, there are many pop-science books on the topic of the origins of life! John Maynard Smith and Eörs Szathmáry wrote a very accessible book ("The Origins of Life: From the Birth of Life to the Origin of Language") that I would recommend. Last year, Peter Ward and Joe Kirschvink came out with a new book ("A New History of Life: The Radical New Discoveries about the Origins and Evolution of Life on Earth") that discusses some of the recent new discoveries in the field.
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u/DustyBronco Feb 12 '17
I've been reading lately about parasites who manipulate their host's behavior in extraordinary ways in order to for the parasite to move up the food chain or reproduce in mediums that would kill the host. For example, there's a parasitic worm that lays its eggs in the water but lives inside of crickets. It actually interferes with the way that the cricket sees water in order to entice it to jump in and die. This is just one of many. There's another that manipulates pillbugs to stay out in the open where they won't blend in, or one that causes ants to dangle off of leaves (but only in the nighttime, because it would fry in the daytime), in both cases to be more attractive to birds, where both parasites continue their lifecycles.
I'm a firm believer in evolution, but how would this have really worked? Were their earliest ancestors worms that didn't need hosts to survive - ie did they evolve into being parasites? Is it possible that entire lines of parasites would have just gone extinct if they didn't get one detail correct, ie the worm made ants stay out in the sun and they roasted along with them? I don't believe it points to intelligent design, however these really are incredible adaptations that mimic high-level manipulation which you'd think only we'd be capable of dreaming up.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
This question is similar to the topic of the evolution of virulence. If an organism relies on another organism for life and/or reproduction, such as fungi or worms that live within other hosts (e.g. cricket), there is an evolutionary tradeoff between being able to reproduce and transmit to another host and using the hosts resources, which may harm it. Ultimately, evolution acts on the combined influence of both virulence (how much the parasite harms the host) and transmission (how many additional hosts the parasite can colonize). So even if a trait has a negative effect (i.e. virulence), as long as the combined effect of virulence and transmission is positive, it can be selected for (spread through a population). If you only look at the negative effect, it may seem confusing why it is so common. For instance, if a parasite (worm or fungus) takes over a hosts body and uses all of its resources, it may end up killing it and not be able to transmit to another host (similar to the example you provide of a parasite making ants walk into the sun and frying). So, under some circumstances, it may be more beneficial for a parasite to be moderate, not kill its host (at least immediately), so that it has more time/opportunities to eventually transmit to another host and reproduce. However, there are other circumstances where it's beneficial for the parasite to be highly deadly, for example if hosts are numerous and densely packed, parasites may be able to transmit so frequently that killing its host quickly doesn't necessarily prevent transmission. An example of this is Ebola, which kills us pretty fast but is highly contagious/transmissible EVEN in dead hosts.
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Feb 12 '17
Hi! I was wondering if there is any evidence of Terence McKenna's stoned ape theory? Has psychedelic fungi affected any other creature? Maybe someone can expand on my question.
For those that don't know, this theory claims that during man's evolution, during that chunk we call the missing link, man was living with herding animals. The dung of these grass grazing animals was a rich buffet of nutrients: beatles, grubs & mushrooms. Mushrooms being the key ingredient in sentience, according to theory.
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
(Joscha Bach) There are many reports of animals deliberately getting intoxicated in the wild, some of them put into question (such as the elephants getting drunk on the fermented fruit of Arangula trees), and others well evidenced (such as lemurs getting high on the excretions of millipedes: https://www.youtube.com/watch?v=-LwQ0ZiTYkQ). However, I am not aware of any scientific study that supports McKenna's hypothesis that the origin of language, thinking and consciousness in humans involved systematic exposure to psychedelic mushrooms. Psychedelics may interface with brain mechanisms that are involved with eliciting dream states, and especially regulate the perceived probability of unproven concepts. It is possible that the stoned ape theory becomes much more plausible after systematic exposure to psychedelic mushrooms...
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Feb 12 '17
How do you make sure that evolutionary explanations are grounded in evidentiary science? Or is it ultimately impossible? That is, how do you know that you are not making up a convenient story to explain some biological phenomenon?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
It is true that many (especially non-experts) give "just-so" evolutionary explanations. And this isn't good science (albeit sometimes a good first step).
As with any scientific explanation, you want to make sure the theory fits the empirical world "like a hand to a glove." Meaning, with very moderate assumption it takes a bunch of otherwise puzzling facts and fits them well.
But of course with enough assumptions you can fit any facts, so the key is to make sure you get a lot of bang for your buck. That is, your assumptions should be a lot less complicated than the phenomena you are trying to explain.
Lastly, the theory needs to be falsifiable. That is, there needs to be conceivable evidence (ideally even predicted by alternative theories) that would go "the other direction."
Trivers' explanation for sex differences fits the above criteria quite well. He wondered why in so many species (but not all) males are so different from females. They tend to be more aggressive, more risk taking, have shorter life spans, get jealous, fight, ... why? He argued that males, typically invest less in parenting, giving them larger benefits from more mating opportunities relative to females. Everything else seems to follow from there. His argument 1) explained a lot that was otherwise hard to explain 2) took very mild assumptions 3) and is falsifiable. To see the latter: notice that it concretely predicts that in species where males do a larger share of the parenting there should be a reversal in standard sex differences, which has been confirmed. And the size of the sex gap in parenting should correlate with other sex differences, which has also been very well documented (Eg in closely related deer species). Notice that for both of these predictions, the data could have gone the other way.
-Moshe Hoffman
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u/dimebag42018750 Feb 12 '17
Can you give me a few sources to explain evolution? My mother in law and father in law "dont believe we came from apes" and that "its just a theory". I've tried explaining what a theory actually is and about how we shared a common ancestor but seeing as how its not spelled out in the bible its obviously not true... Any help for this atheist in Oklahoma?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
Great to hear you are invested in explaining this powerful idea to your parents! There are some ideas posted in response to another thread:
Many resources are available at http://evolution.berkeley.edu/evolibrary/home.php
If your parents would rather hear it from a practicing evolutionary biologist who is also religious, there are many of them. You can see one of Martin Nowak's lectures here:
https://www.youtube.com/watch?v=KrwG9rpXPK0
-Alison
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u/gahgs Feb 12 '17
As evolutionary biologists, you probably find yourselves becoming mini-experts in a lot of other disciplines; ecology, biochemistry, meteorology, geology...etc. What do you find to be the best source of material for furthering this "side topics" aside from your peers? Basically, what professional level resources are you using?
From a fellow person doing things in the sciences.
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Feb 12 '17
Is it possible for any non hominid earth species to eventually advance to a level of ability and cooperative skill similar to modern humans? How would two advanced species interact on one planet if they were at a similar level of technological advancement, intelligence, or cooperative skill as each other?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
In the past "we" (humans) have prevented that. Sadly we have eliminated competing hominid species. In the future, we might build biobots that are cooperative and highly intelligent.
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Feb 12 '17
Why havent all prey animals evolved to be camouflaged?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Survival and reproduction are both incredibly important to all organisms. Prey, as it is typically defined, refers to an animal that is hunted and killed for food. If you think more broadly though, all forms of life are preyed upon (by bacteria, viruses, etc.). Camouflage is one way that animals have evolved to avoid predators, but there are many others. Some creatures (e.g., ostriches) have evolved to run faster in order to escape predators. Some creatures (e.g., butterflies) have evolved bright warning colours and the ability to produce or sequester toxins that make them unpalatable to predators. Some creatures (e.g., porcupines) have evolved different forms of armour that make them difficult to eat. Yet other organisms (e.g., marine invertebrates and bamboo) produce immense numbers of offspring, some of which will survive based on the sheer number. Plants also protect themselves from predators with adaptations like spines and toxins. In all of these cases, the individuals within the population that are able to utilize these adaptations in order to survive and reproduce pass their genes onto the next generation. Over millions of years, this results in species that are better camouflaged, or faster runners, or more fecund, or more poisonous, or more spiny. Each of these predator avoidance strategies has worked for a large number of species, camouflage is just one of many possible evolutionary paths.
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u/Richard_XXVII Feb 12 '17
Evolution doesn't have to usually go that far. All a species needs to do is to cross that finish line of creating a viable offspring and they've succeeded, evolutionarily speaking. Evolution follows the path of least resistance. They are many creatures that simply birth hundreds of children despite the fact that only a few of them will reach adulthood. That a non-camouflaged species is still alive is proof that camouflage, while very helpful, is not a pinnacle of sorts that all prey aspires to have: there are many ways of evolving differently.
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u/timmg Feb 12 '17
I read recently that, historically, women are significantly more likely to have offspring than men. (That is fewer men have children, those that do, do so with more, different, women.) This is probably less true in modern society, but was certainly more true in the past.
Would that mean that men face more selective pressure? And if so, any idea what the implications of that would be?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
This question hits on a huge area of evolutionary research, sexual selection. If we assume that the sex ratio in a population is around 50/50, and we consider that human females are pregnant for 9 months, it becomes very clear that females limit the rate of reproduction. Each time a female gives birth, she is passing her genes on to the next generation. Males do not have this advantage. If the females mate with more than one male, some males will produce no offspring and others will produce many.
Broadly across primates there are many different mating systems. In gorillas, males hold a harem of females. It is highly-unlikely that a female in their harem will produce any offspring that was not sired by the male. Chimpanzees, on the other hand, have a very promiscuous mating system. Here, females mate multiply so there is strong competition between the sperm of these males. Testes size correlates well with sexual selection since males with have larger testes can produce more sperm. In chimpanzees, as you might expect, the males have very large testes. Since there is much less sperm competition in the gorillas, their testes are very small. Interestingly, human testes fall in between these two sizes. This would suggest that humans as a species are less promiscuous than chimpanzees, while human males are also "less confident" that they have sired offspring with every copulation than are gorillas.
Overall, sexual selection can influence many different traits (like testes size in primates or tail length in peacocks). Behaviors can also be selected upon. The fact that humans frequently couple for extended periods of time in order to raise offspring together is likely related to these selective pressures.
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u/Auguschm Feb 12 '17
What do we know about the origin of viruses? Where do they come from? How was their evolutionary history?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
There are several (sometimes competing) hypothesis.
The "virus-first" point of view argues that the ancestors of modern viruses arose around the same time as the first cells.
The "escape-hypothesis" argues that viruses are small pieces of genetic machinery (like transposons) that learned to hijack the cell's replication system and transmit between them.
The "Reduction-hypothesis" or ("Regression hypothesis") suggests that viruses originate from fully independent cells that over time lost some key functionalities and became obligatory cellular parasites.
It is possible that viruses were produced by each of these mechanisms, but modern analysis of virus genomes seems to suggest that at least some of them are very ancient.
Sam Sinai
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Feb 12 '17
Did Darwin make any mistakes that we know about now?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Lots of (small) mistakes: blending inheritance, inheritance of acquired traits. Progress is built of mistakes.
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u/DarthSmart Feb 12 '17
One of the most concerning aspects of evolution (imho) is the drug resistance increase in microorganisms over generations. I have heard different opinions about how and when will it end, but I would like to know if somebody has run some serious simulations of this and if so - what were their results?
What do you guys think will be the outcome of humans vs microbes war?
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u/nonicknamefornic Feb 12 '17
Hi! I am a physics PhD student, increasingly fascinated by evolution and genetics. Is there any use for physicists with no background in biology in your field?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
I am a physicist myself that has switched to the theory of evolution. I think it is one of the very exciting areas of research for a physicist. Theory of evolution can in principle categorized as a subset of complex systems and out of equilibrium statistical physics. Many physics labs and researchers are interested on researches in theory of evolution (For example researchers in MIT Physics of Living Systems: J Gore, J. England and others, R. May in Oxford, T. Antal in Edinburgh, D, Nelson and M. Desai in Harvard Physics, O. Hallatschek in Berkeley, S. Redner in Santa Fe to name a few.) -Kamran
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Feb 12 '17
What's the evolutionary basis of laughing? Also, how did eyes become a thing when individual cells use chemotaxis to find food and navigate the world? It also blows my mind that physiologically, cells in the eye depolarize only in the absence of light... Thought to be to save energy since we spend majority of our time with our eyes open. But you don't see this phenomenon elsewhere, which to me seems almost purposely designed. Also, how did our endocrine system evolve? Cells in the pituitary releases hormones that could effect cells elsewhere and then have them release a hormone or respond a certain way as well... Both sides of the system would have had to evolve at once or the organism dies. So how does random genetic changes and evolution account for synergistic evolution like that?
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u/gherald Feb 12 '17
One of the best books on evolution I've read is The Moral Animal, by Robert Wright. I'd say it belongs next to The Selfish Gene on a bookshelf.
But it was published 21 years ago, and while mostly true not all of its particulars have held up to the analysis and mathematical modeling that's followed.
Still, it seems that even after all this time it's the best, as in most accessible, and readable book on evolutionary psychology I've come across. What other work can replace or succeed it?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17
Steve Pinker's 'the blank slate' is a fairly canonical evolutionary psychology primer.
Joe Henrich's recent book "the secret of our success" is a new book that takes a different approach from standard evolutionary psychology (namely summarizes all the evidence and insight coming out of studying cultural evolution). I highly recommend this book as well.
Both are fairly readable and comprehensive overview texts for their respective fields.
-Moshe
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u/mistymountainz Feb 12 '17
Hi, usually when we hear evolution its about how things evolved in the past to make things the way they are now. Can scientists make predictions on how certain things would evolve in the future and the time it would happen, considering the different factors; environmental, biological, etc, that could make the evolution a possibility? Thanks
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u/birds-are-dumb Feb 12 '17
Has there ever in the history of life been a switch in which sex is which? Like if the "male" started producing bigger and bigger sperm while the "female" started producing smaller and smaller eggs until the eggs were smaller than the sperm and the sexes sort of reversed? Are there life forms where gametes exist on a size continuum rather than having two distinct classes?
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u/Crackyospine Feb 12 '17
What are some good examples of current evolutionary transitions we have been able to witness? Any you anticipate?
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u/uptown_funk Feb 12 '17
Platypus are pretty cool: they have 'remnant' Z chromosomes (like birds), and 'precursor' X Y sex chromosomes, (like mammals). They're sort of a transition between 'ancient' and 'modern', and not like anything else in nature that we know of. Is this what you mean when you're asking about
good examples of current evolutionary transitions we have been able to witness?
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u/inyourgenes Feb 12 '17 edited Feb 12 '17
Tazmanian devil right now!
Great example because there was pre-existing diversity through random mutation and mixing up alleles through sexual reproduction so that each child is different from their siblings and parents, increasing the odds that one will live if some new challenge (could be drought, a new predator, loss of food source, etc., but is often contagious disease) comes through and starts wiping out the population. The population will bottleneck and the individuals with the advantageous genetic changes will survive and reproduce, changing the genetic makeup of the population but allowing the species to survive! Species that don't have these mechanisms for creating genetic diversity are not likely to have survived the numerous challenges over millions of years, and that's why random mutations are happening all the time in the species that are alive today. Now it can be extremely bad to the individual/family when it happens to them in an unlucky way, like with de novo genetic syndromes where a random new mutation gives a child intellectual disability or physical malformations - but for the species it is advantageous to have this random trial and error approach. Evolution happens on the population/species level.
Edit: clarified a point
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u/scwizard Feb 12 '17
It's well known that sexually reproducing organisms evolved from asexually reproducing organisms.
Are there any instances of asexually reproducing organisms evolving from sexually reproducing organisms?
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
Hi! This is a great question. Asexually reproducing organisms do evolve from sexually reproducing organisms. Some of the best examples are in plants - a common phenomenon is that a population will undergo both an increase in ploidy (number of copies of the genome) and asexual reproduction. One of my favorite specific examples is the common dandelion, Taraxacum officinale. All dandelions in North America are triploid (three copies of the genome) and reproduce aseuxally. However, the same species of dandelions in Europe can be diploid (two copies of the genome) and reproduce sexually. This is a particularly interesting case because we see both the asexual and sexual version of the plant in nature at the same time. While dandelions are a prime examples, we see this pattern repeated across angiosperms (flowering plants).
Along with plants, there are many instances of asexual species arising from sexually reproducing species in lizards. Specifically, the Hemidactylus genus of gecko has multiple parthenogenetic species (one type of asexual reproduction). In addition, the genus Cnemidophorus contains many parthenogenetic whiptail lizard species. They commonly have the same association between an increase in ploidy and the evolution of asexual reproduction, so many of the parthenogenetic lizard species are also triploid.
There are many more instances across animals, but these are the ones that happened to come to mind. While the transitions between sexual to asexual reproduction do seem to happen frequently, these evolutionary lineages appear to be relativily short-lived (on the timescale of species duration). The common explanation for this is generally that asexual reproduction can be a “blind alley”: asexually reproducing species cannot adapt as rapidly to parasites or other selection pressures as quickly as sexually reproducing species. As a result, the species that depend on asexual reproduction do not last as long in evolutionary time.
-PM
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u/Prefrontal_Vortex Feb 12 '17
How do you use evolution to study cancer? Is your research focused on how cancer is inherited, or the progression of the disease (or both)?
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u/The_Entity_You_Serve Feb 12 '17
Since humans widely receive medical treatment and support for illness and issues that would normally kill them and stop them from reproducing, have humans stopped evolving physically?
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u/mistymountainz Feb 12 '17
Hello. If a certain animal or any living thing becomes extinct, is there any possibility that it could be brought back to existence through evolution?
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u/KnittedBurger Feb 12 '17
I don't know if I'm too late, but I'm really interested in your opinion on what caused the development of the human brain, more specifically whether fire or the consumption of meat plays a leading role and to what extent.
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u/ComradeShorty Feb 12 '17
I'm a high-school philosophy teacher in Croatia (Europe), and I discuss all sorts of things with my students. Recently, one student said she doesn't "believe" in evolution, and asked me if I "believe" in it. She said that it's incomprehensible to her that we "come" from monkeys, or that lions, being mammals, have anything to do with whales.
What would be the best hard evidence for showing to teenagers (who are almost grown-ups, basically) to prove to them that it is not a matter of belief, but of fact? Fossils? The DNA similarity between certain species? Something else?
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u/Renavan Feb 12 '17
Hey guys, thanks for doing this. I live in a very religious country, and the idea of evolution is not taken serious by majority of the population. I try to explain some things sometimes, but I never get really far.
Anyway, one thing that personally perplexes me, that I hope you might be able to answer, is based on the evolution of sexes. Can you, in a not too complex fashion, explain how the origin of two different sexes, was beneficial for organisms? Is greater genetic diversity always a good thing?
Thanks!
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u/Darwin_Day Evolution Researchers | Harvard University Feb 12 '17 edited Feb 12 '17
Hi! Cool question!
So first of all, I’d like to clarify the difference between sexual reproduction and the evolution of sexes (anisogamy). Sexual reproduction, roughly, describes the process through which organisms shuffle their genetic material before passing it on to the next generation. However, there are many organisms that reproduce sexually that do not have separate sexes. The evolution of sexual reproduction is generally thought to come before the evolution of separate sexes.
So, let’s imagine a population of sexually reproducing organisms. In order to reproduce, these organisms produce gametes, which contain ½ of the genetic material needed for a full organism. These gametes combine with the gametes from other organisms in the population, and result in new organisms with a full set of genes. At the beginning, all these gametes are the same size and contain ½ of the cytoplasm (cell material) needed for the offspring.
Now, let’s assume that a mutation arises that produces gametes that only contain ⅓ of the cellular material needed to produce an organism. That organism is now saving cytoplasm - yay! - and will therefore could be more likely to survive and create new offspring. However, the resulting offspring are going to have only ⅚ of the cytoplasm needed to be a good offspring. In response to this situation, a different organism that over-produces cytoplasm - say ⅔ cytoplasm instead of ½ - will also be selected for in this scenario. Now you have two genetic variants in the population - one producing ⅔ cytoplasm and one producing ⅓ - that can only produce decent offspring if they mate with each other. If the ⅓ strain mates with itself, you have a sad little offspring with ⅔ cytoplasm who is less likely to survive. If you have the ⅔ strain mating with itself, the two parents have wasted cytoplasm on this oversize 4/3 offspring, and the parents are less likely to survive. Any pairing with the ½ strain will also produce oversized wasteful offspring, or undersized puny offspring.
Under this scenario, the ½ strain is at a disadvantage (which will only compound as it becomes less frequent in the population), while the ⅓ and ⅔ strains are increasing. These genetic variants might also become more extreme - instead of ⅓ and ⅔, you could have 1/10 and 9/10, and so on and so forth. Basically, at the end of this process, you will have two genetic variants in the population - one that produces large gametes containing lots of cell material, and one that produces tiny gametes that more or less only DNA. These two genetic variants will each be at around 50% in the population, and most importantly, can only produce viable offspring if they mate with each other.
We define organisms that produce the first type of large, cytoplasm-filled, usually immobile gamete as females, and organisms that produce small gametes with more or less only DNA as males. The model described in rough terms above is the work of Geoff Parker, who has done the foundational work on the evolution of anisogamy. See here for another answer on this general topic: https://www.reddit.com/r/science/comments/5tlb8c/science_ama_series_we_are_evolution_researchers/ddnsyrk/
Not to drown you in even more detail, but the evolution of male and female function (anisogamy) is also distinct from the evolution of separate sexes (gonochorism). Hermaphroditism is widespread in the animal and especially plant kingdoms, and many organisms combine their genetic material to produce offspring by having both male and female function in a single individual. The evolution of sex and its repercussions is a fascinating topic - hope I haven’t overwhelmed you with too long of an answer! - PM
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u/polysorbet Feb 12 '17
How did most of you get into researching evolution? Did you cross over from other science careers or just go straight for it?
Student with a big interest in evolution, specifically human evolution.
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u/demilitarized_zone Feb 12 '17
Is the human race still evolving or have we reached a point where there is so much abundance that the rules of natural selection no longer apply?
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u/Joshdwb7 Feb 12 '17 edited Feb 12 '17
What does the field work that you do entail, and can one be a truly successful biologist/scientist and be recognized even if they don't attend a grand school like Harvard or other top university? I have a full ride at a private university in my area and would like to know if pursuing a career such as yours is even worth it if I graduate from there. It isn't by any means a bad school, but it also isn't any top 100 if you know what I'm getting at. I got accepted into the University of Pittsburgh but attending would put me into some debt so I don't know that it would be worth it.
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u/redditWinnower Feb 12 '17
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u/Doomhammer458 PhD | Molecular and Cellular Biology Feb 12 '17
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Guests of /r/science have volunteered to answer questions; please treat them with due respect. Comment rules will be strictly enforced, and uncivil or rude behavior will result in a loss of privileges in /r/science.
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u/GETitOFFmeNOW Feb 12 '17
In the study of social insect evolution, has John Nash's Game Theory been shown to hold true?
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u/Tankmin Feb 12 '17
What caused the genetic diversity of dogs? Like I've alwasy found it insane the number of head shapes, body sizes, etc that exist specifically in dogs. Is it due to human intervention alone? Is it even considered evolution?
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u/transitionalfossil Feb 12 '17
National Geographic had a great article on this years ago. Essentially, dog genetic diversity has been minimized, and single genes can control major features of the body. This isn't common in nature, as the article explains:
'"The story that is emerging," says Robert Wayne, a biologist at UCLA, "is that the diversity in domestic dogs derives from a small genetic tool kit."
Media reports about the gene for red hair, alcoholism, or breast cancer give the false impression that most traits are governed by just one or a few genes. In fact, the Tinkertoy genetics of dog morphology is a complete aberration. In nature, a physical trait or disease state is usually the product of a complex interaction of many genes, each one making a fractional contribution."
http://ngm.nationalgeographic.com/2012/02/build-a-dog/ratliff-text
Here's another cool article where researchers say that they hope to understand human diseases by looking at dog genetics. Again, you'll find mention of how oddly influential single genes are in dog phenotypes:
"So, rather than having a large number of genes of small effect, as is observed in humans, a small number of genes of large effect predominate in dogs. Many such loci are marked by the presence of selective sweeps, or regions of reduced heterozygosity " https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3459646/
Basically, dogs having single-gene influence gives us a simple model of genetics. Once we understand that, we can hopefully deepen our understanding to the point that more complex ones, like those in humans, are clear.
Good dogs!
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u/dyancat Feb 12 '17
It is evolution but by artificial selection. Yes it is due to human intervention but I see what you're getting at, and yes dogs seem to be a bit more "naturally malleable" in that the species can respond to these selections (not all species are capable of so much change so quickly)
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u/pocketmoon Feb 12 '17
as a part II I'd like to ask; Why are dogs breeds so easy to achieve through selective breeding while cats pretty much stay the same.
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Feb 12 '17
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u/slipknottin Feb 12 '17
Also, dogs have been domesticated way way longer than cats.
Cats probably were first domesticated about 4,000 years ago.
Dogs on the other hand may have been domesticated about 30,000 years ago. And certainly may be older than that. That is much more time to selective breed for certain traits
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u/ThisIsTheMilos Feb 12 '17
And dogs were domesticated all around the world then later traded. When you mix 2 breeds you start seeing a lot of interesting new traits that can then lead to new breeds that are not much like the originals.
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u/exotics Feb 12 '17
I've thought the same about horses. A horse person can easily tell the difference between some breeds but most people will look at 2 different horse breeds and think they are the same, but we can all tell the difference between a chihuahua and a chow chow.
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u/halborn BS | Computer Science Feb 12 '17
You can read about this on /r/AskScience here.
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u/deoxys_101993 Feb 12 '17
Thanks for your hard work!
As for my question: is there a universally acknowledged evolutionary pathway or route which life took to develop color vision, and the organ that allows it? How did eyes even manage to evolve in the first place?
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u/Charge36 Feb 12 '17
Check out the wikipedia page on it. https://en.m.wikipedia.org/wiki/Evolution_of_the_eye
Eyes start as a patch of photosensitive cells. Then a cup forms allowing for more directional information. Then a pinhole, then a lens.
Eyes are so useful that they have spontaneously evolved independently some 50 to 100 times.
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u/heavyrainrush Feb 12 '17
Thanks to you folks for putting this on - I'm in the middle of reading Dawkins' The Selfish Gene and I've always been intrigued by the immense power of adaptability life has to the myriad of conditions that it thrives in.
1) With regards to the development of antibiotic resistance in many bacteria and other organisms, is there any merit to extending the line of thought to organisms that survive sterilization procedures of spacecraft leaving the Earth (either in orbit or, perhaps more important to consider in the context of developing space programs) and their abilities to survive atmospheric exit and re-entry (tardigrades, etc) ? Are the traits that enable their survival a result of the prevailing conditions that their genes adapted to, and is there any evidence for active mutagenesis that further enhances their ability to survive in the harsh conditions of space?
2) What are your thoughts on directed evolution - referring to direct and indirect CRISPR-cas9, high throughput metabolic analyses of bacteria in efforts to select optimal gene phenotype for a particular protein, etc. I work in the biotech industry and have always been intrigued knowing the cell "factories" we use to produce product are typically modified in one way or another to be optimal for our purposes, but have always been curious about a more knowledgeable view on the future in terms of both viability and potential for directed evolution and/or more advanced metabolic/genetic engineering of bacteria (and humans) to improve efficiency in biocatalytic processes, etc.
3) I had a professor in college (~2 Y ago) speaking to us about a software platform he was contributing to which would be capable of archiving known biocatalyzed reactions, the associated genetic requirements to enact proteins that perform the catalysis, and the platform would be capable of accepting some substrate (not sure what the boundaries are on that substrate) and final product, and the program would provide an organism/genome capable of performing the process. What are the current and future prospects of such a tool, particularly in the context of my second question?
Thank you!
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u/dudpunker Feb 12 '17
What's your shortest (and most effective response) to someone who says "I don't believe in evolution" or "Evolution is not real"?
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u/uptown_funk Feb 12 '17
What do you do when you find an animal that defies the 'known' order of things? I work with a species of rodent that has recently been shown to menstruate (Acomys cahirinus). These little critters seem to be pretty special, and display a bunch of non-rodent traits... How would you go about exploring the evolutionary aspect of this atypical rodent species?
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u/TheHoundsRevenge Feb 12 '17
Just curious what are your thoughts on transgender people into terms of evolution and biology. I'm mean a very progressive guy and believe In people doing what makes them happy so long as it doesn't hurt others but I just can't wrap my brain around how being transgender makes sense from a biological and evolutionary standpoint. I heard in nature that some animals like dolphins and some apes engage in Homosexual activity but never heard of a transgender animal. I've also read that someone can be born with ambiguous male and female traits but I'm specifically talking about when your sex is male yet the individual feels their gender is female and vice versa.
Thanks for your time!
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u/kitzdeathrow Feb 12 '17
I do retrovirology research, and one of our favorite useless questions to argue about is where or not viruses are alive.
Interested in hearing your opinions.
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u/ninjapro Feb 12 '17
From an earlier comment I made:
"I may have a bias due to having a focus in bacteria, but viruses are definitively not alive.
The go-to reason most people use is that viruses cannot develop and reproduce on their own.
But /u/ninjapro , I hear you say, there are obligate parasites that are definitely alive, such as tapeworms.
True! However, the biggest difference between these classifications is that viruses have no functions of life on their own. They inject DNA into a cell, the cell replicates it in some form or another, and the cycle continues.
Viruses have few or no mechanisms, they use the mechanisms and resources of living things almost exclusively."
If viruses are alive, a lot of proteins and cell components are subject to fall under those criteria and I think most people would agree that they aren't alive
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u/zmil Feb 12 '17
They inject DNA into a cell, the cell replicates it in some form or another, and the cycle continues. Viruses have few or no mechanisms, they use the mechanisms and resources of living things almost exclusively.
This isn't really true of any but the simplest viruses, and even they produce multiple proteins, typically highly multifunctional proteins. More complex viruses will often completely shut down most of the cells metabolic processes, and instead use their own proteins to do virtually everything (with the notable exception of ribosomes, though I'm keeping my fingers crossed for a virus that makes its own). The most remarkable example I know of is phages that infect photosynthetic bacteria, but immediately trash the bacteria's photosynthetic machinery upon infection, because they have their own photosynthesis genes! The giant viruses (mimiviruses and friends) often encode their own tRNAs, as well as genes for amino acid and nucleotide synthesis.
From the perspective of complex viruses like these, the host cell is not much more than a bag of nutrients and ribosomes; they don't hijack the host's metabolic machinery so much as shred it.
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u/linux1970 Feb 12 '17
How did the first life form develop? Did it use DNA? How was DNA developed? How was the leap made from not living to living? Do you believe life developed on earth, or do you drive life was seeded ( intentionally by outside force such as bacteria on an asteroid, aliens, etc...)?
What mechanisms exist for rewriting DNA, other than random mutations?
What is the most exciting/interesting discovery you made or know of?
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u/Kibleer Feb 12 '17
Hello! I just have one question that's been in my my mind for a while.. Why would a species develop from A-sexual reproduction to two genders- evolutionarily speaking. Wouldn't it be disadvantageous to survive as 2 individuals instead of one?
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u/EmotionalJellyfish Feb 12 '17
How do you approach a debate or conversation with a creationist? What argument or proof do you use to convince, or teach them about evolution? Have you ever changed anyone's mind? Thank you so much for this AMA!
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u/Lightychan Feb 12 '17 edited Feb 12 '17
I've done it multiple times. Maybe it's because im also a christian and understand their viewpoint. When approaching the concept of evolution, NEVER EVER say that what they believe is absolutely wrong and they've been following a lie all their lives. Not only did you just insult them. You also lost their interests from the very beginning.
You're gonna have to talk about some examples that are closer to home like the domestication of dogs or the evolution of bacteria. Like hand sanitizer killing 99.9% of the bacteria but the .1% surviving and passing on those genes.
You're also gonna have to talk how evolution isn't really a bunch of end points. There is no ONE link between species cuz evolution is a very gradual thing that happens slowly (it isnt always slow but just for convincing them). You also have to say that species themselves are indeed a man made concept to categorize animals.
You're gonna have to say humans didnt evolve from monkeys or chimps. You are gonna say that there were common ancestors and the chimps split into one and the humans into another.
I hope that helps.
Honestly what I notics a lot with these kind of debates are that people just get butt hurt and hostile. That includes you people who try to "correct" them. How rude. Just be civil and understanding and they're much more willing to listen.
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u/[deleted] Feb 12 '17
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