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!

Abstract

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I know this is a basic question, but I feel it's very important - especially in today's political climate:

If you were speaking to someone who doesn't believe in evolution, what would be the simplest, most powerful proof that you would give them?

I come from a community that believes evolution is made-up heresy (shockingly, 33% of Americans fit that description nowadays), and I don't have a clear, convincing basic proof to give whenever the conversation arises.

Thank you very much!

oomobi

This is a great question, and many others have posted great answers already! It’s hard to come up with one really simple story. Our group here has a few different philosophies.

Some of us think it’s most convincing to explain the basic ingredients of evolution: if you have heritable variation in a trait within a population (e.g. “mutations”), and then you have competition for survival, and if that trait improves survival, individuals who have that trait will be more likely to survive and reproduce, and they’ll pass that trait onto their offspring, and over time, the population will have more and more individuals with that trait. That logic is pretty easy to follow, and from that, evolution will occur!

But often people who belong to communities like yours do indeed believe these basic tenants, they just don’t believe that these mechanisms could lead to all the complexity we see in life on earth. This is actually pretty understandable, because the timescales for evolution in large animals are just sooooo slow .. millions of years. Humans are really bad at understanding long timescales because it’s just so out of our realm of experience. That’s why sometimes stories of evolution in short-lived organisms, like antibiotic resistance in bacteria, are good. In even a few years we can see bacteria change their genetics and their behavior and it has real life effects for everyone! Or the flu virus, evolving away from the human immune system and the flu vaccine every flu season.

As others have mentioned, there are some nice stories of traits that animals have that are the sometimes circuitous path of evolution, and seem like they’d be pretty dumb to put into a “designed” organism. For example, why do whales have fingers in their fins and bats have fingers in their wings? Why do humans have a appendices or tailbones or an unnecessary forearm muscle used to contract claws in some animals? Why do we have a blind spot in our eyes? Why is our throat designed such that we have such a high chance of choking to death? Why are babies heads and female pelvises so similar in size that childbirth is so dangerous in our species?

Also, thinking about artificial selection - such as dog breeding - helps many people. With artificial selection we humans impose a selection on an organism, choosing who will reproduce, and over time we can get crazy changes! Beyond dogs, most food we eat today has been artificially selected to look totally different than how it did before human agriculture. Natural selection just occurs much much slower.

Charles Darwin himself actually had the exact same problem as you - and his books are surprisingly easy to read (such as the Origin of Species). He gives tons of examples beyond what I’ve mentioned here. One cool one is mentioned here: https://www.theguardian.com/science/lost-worlds/2013/oct/02/moth-tongues-orchids-darwin-evolution

-Alison


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.

avant-garde_funhouse

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


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.

avant-garde_funhouse

(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.


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.

avant-garde_funhouse

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.


Is there any evidence for continued evolution of homo sapiens? If so, what are your predictions on how we will evolve in the future?

pharmaste

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


How does homosexuality arise in certain species?

ndndnd182

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


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?

arpie

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.


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?

Brolee

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


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.

MyNamesNotRickkkkkk

Please take a look at the book "Evolutionary Dynamics" by Martin Nowak. It is a simple summary of the basic principles.


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.

MyNamesNotRickkkkkk

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


How has the understanding of epigenetics changed your study of evolution?

intronert

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


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?

RyanABWard

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.


Do you consider viruses as life being creatures? And for which reasons?

metablood

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


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?

SkepticShoc

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


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?

SkepticShoc

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.


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)

mantis-_-tobogan

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

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.

travel_takeover

(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.


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)?

mutual_im_sure

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!


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?

ChaosHellTV

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.


How do you feel about the RNA world hypothesis? Could RNA have existed exclusively as the first self-replicating molecule, or do you believe peptides must have been involved?

NotABiscuit

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


How do you feel about the RNA world hypothesis? Could RNA have existed exclusively as the first self-replicating molecule, or do you believe peptides must have been involved?

NotABiscuit

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.


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?

prolapse_popper

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.


Do you have colleagues that refuse to give up their religious beliefs or timelines despite the evidence for evolution? How do they reconcile it?

powerglover81

(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.


Do you have colleagues that refuse to give up their religious beliefs or timelines despite the evidence for evolution? How do they reconcile it?

powerglover81

Evolution is not at variance with meaningful religious beliefs. Evolution does not contradict theology, in the same way as evolution does not contradict philosophy.


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?

pimpologydoctorate

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


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.

ethylnaut

(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...


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.

DustyBronco

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.


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!

DrakePecker

(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.


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!

DrakePecker

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.


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!

DrakePecker

These are very good questions. Some of them are not yet answered. Please look at at http://ped.fas.harvard.edu/files/ped/files/pnas08b_0.pdf


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?

fraubot

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


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?

fraubot

One possibility is to study evolutionary phenomena in a lab setting. For example, researchers study the evolution of micro-organisms over many generations and see which mutations arise and what their consequences are.


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?

SandDab

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.


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.

gahgs

I enjoy the interaction with computer science. Both evolution and computer science are about information. Also there is a strong link between understanding the principles of evolution and mathematics.


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?

dimebag42018750

Great to hear you are invested in explaining this powerful idea to your parents! There are some ideas posted in response to another thread:

https://www.reddit.com/r/science/comments/5tlb8c/science_ama_series_we_are_evolution_researchers/ddnc7d5/

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


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?

timmg

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.


Why havent all prey animals evolved to be camouflaged?

RJturtle

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.


Why havent all prey animals evolved to be camouflaged?

RJturtle

There are different strategies of anti-predator behavior. For example, moving very quietly, tremendous sense of hearing, smell, enormous speeds. But some kind of camouflage is often involved.


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?

DarthSmart

With current policies we will lose that war. Bacteria will become resistant to essentially all the antibiotics we have now. The question is if we can come up with completely new tools.


Did Darwin make any mistakes that we know about now?

redenwolf

Lots of (small) mistakes: blending inheritance, inheritance of acquired traits. Progress is built of mistakes.


Did Darwin make any mistakes that we know about now?

redenwolf

(Joscha Bach) Darwin married his first cousin. Some researchers suspect that this had negative effects on their children; three of the ten died before reaching the age on ten, and another three did not have any offspring. (Their marriage was a happy one though.)


What do we know about the origin of viruses? Where do they come from? How was their evolutionary history?

Auguschm

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


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?

nonicknamefornic

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


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?

nonicknamefornic

Yes. Physicists like Robert May (Oxford) or Tibor Antal (Edinburgh) have revolutionized our field.


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

mistymountainz

Predicting evolution in a small, well defined context is possible. Predicting macro-evolution of a global species is harder. I expect people are currently building the next stage of biological organization. These are robots, maybe bio-bots; chips and the internet.


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?

scwizard

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


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?

gherald

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


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)?

Prefrontal_Vortex

On both. And on treatment. We are very interested in evolution of resistance to treatment. And how resistance could be prevented. http://ped.fas.harvard.edu/files/ped/files/elife13a_0.pdf


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?

MDfootball2014

I would say laughing is related to social bonding. It is a sign of agreement between people. It could come about by sexual selection. You prefer a partner with a good sense of humor.


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?

The_Entity_You_Serve


What is your favourite evolutionary trait?

BigCoela

Sam here. Mine is cooperation, which is the basis for many important evolutionary transitions, including evolution of multicellularity, societies and technology. A more "concrete" trait would be language. It allows for cooperation, provides a rich medium for cultural evolution, and last but not least, lets me communicate this thought over the internet.


What is your favourite evolutionary trait?

BigCoela

Life itself.


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?

ComradeShorty

DNA similarity is a perfect argument.


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?

mistymountainz

Charleston here. It's not absolutely impossible, but it's very unlikely. If you would consider human intervention to be a product of evolution, it's looking increasingly likely that we could "de-extinct" species technologically: http://www.sciencemag.org/news/2016/09/should-we-bring-extinct-species-back-dead


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.

KnittedBurger

The main selection pressure for bigger brain came from social politics, language, indirect reciprocity.


Hello and thanks for the AMA!

I only just realized that it is Darwin's Birthday, and coincidently me and my wife are currently in the Galapagos island - what an honor it is to follow his footsteps.

My questions thus iare - what are some observations I can make today that would help me better understand Evolution? What are some of his writings that I should take note of that I can apply during my time here?

Also - if I did an about turn of my career and studied in biology, would I be able to find work and/or are there areas of research left to be explored?

We visited his statue and the Charles Darwin research center yesterday which I thoroughly enjoyed, it is wonderful to see how his memory is kept alive here, and how they honor his lifes work, while actively protecting these magical islands.

Lastly a more controversial question - how would I go about explaining evolution in a way that someone who simply does not believe it (my dad -.-) would better understand it?

Thank you so much for everything you do!

FRIENDLY_CANADIAN

Enjoy your beautiful trip!

A good argument for evolution is DNA similarity among primates for example.


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?

birds-are-dumb

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?

Carl Veller: Great question. I should first point out for other readers that, as your question suggests, “males” and “females” are usually defined by biologists according to the size of their gametes: females, by definition, produce larger gametes. Size differences in gametes (“anisogamy”), and therefore a separation of sexes, have evolved many independent times in the history of life -- the dominant theories for why this should have happened are due to Geoff Parker.

The initial choice of gamete size divergence appears to be very stable over evolutionary time, which explains, for example, the many other physical correlates of males and females that we recognize in, say, mammals (one checks a dog’s sex by methods other than extracting gametes and measuring their size!).

Exceptions exist, though. Males in the fruit fly species Drosophila bifurca are just a few millimeters long, but produce sperm with such long tails that, when unravelled to their full length, are about 6cm long! When these are rolled up, as is their usual state I think, they are still smaller than eggs from females of the same species, but not by much. In explaining this evolutionary increase in sperm size back towards the size of eggs, it is important to note that female Drosophila bifurca usually mate with multiple males. Very large sperm could then be a way to block a female’s reproductive passage to the sperm of males who subsequently mate with her. Alternatively, because females can store the sperm of several males (in a special organ called the spermatheca), and show signs of being able to then select which sperm to use to fertilize their eggs, larger sperm might also be more attractive to the female. These benefits to larger sperm size would need to be sufficiently large to compensate for the reduction in sperm number that comes from devoting many resources to each individual sperm.

As for a size continuum of gametes within a species, I am not aware of any examples.


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.

polysorbet

Because evolution touches nearly every other field in the biological sciences, many scientists who are currently studying evolution began in other fields: ecology, genetics, biophysics, mathematics, just to a name a few. But many other evolutionary scientists have been studying evolution for their entire careers!

Human evolutionary biology is offered as its own undergraduate or graduate program at some universities in the U.S. and around the world, and if that is your primary interest, then it is a great idea to join one of these programs or take courses that they offer.


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.

polysorbet

I came into evolution from biochemistry. Then I was fascinated to understand the mathematical principles of life. This is still the biggest fascination for me.


What do YOU believe the origin of life is?

I'm partial to the whole star trek seeding thing.

darth_chez

Most likely there was a spontaneous origin of life from prelife, from generative chemistry, on Earth about 4 billion years ago.


What are some good examples of current evolutionary transitions we have been able to witness? Any you anticipate?

Crackyospine

I can recall two prominent examples:

  1. Evolution of multicellularity. In various experimental setups researchers are able to observe evolution of staying together (formation of multicellular complexes) as well as evolution of division of labour. One of the examples for experimental setups are in algae (Volvox). (See ‘Multiple origins of complex multicellularity’ by A. H. Knoll. Also there are lecture series in iTunes U (esp first lecture) https://itunes.apple.com/us/itunes-u/evolution/id413141276?mt=10

  2. Cancer evolution. It is now well established that cancer is an evolutionary diseases. A complex multicellular evolutionary structure can be vulnerable to the appearance of ‘selfish’ single cells that do not follow evolved cooperative behaviour among other cells. A malignant somatic mutation - in an adult stem cell niche - can initiate cancer. The growth advantage of mutant cells due to elevated division rates or escaping regulatory pathways leads to carcinogenesis. (For example see recent experiments in coloretcal cancer: http://www.nature.com/nrc/journal/v14/n7/abs/nrc3744.html) Cancer might be thought of as the result of a transition from a complex multicellular structure to a simpler one (though there is lots of evidence for rudimentary structure within cancer cell populations).

    See Bob Weinberg book, 'The Biology of cancer', Chapter 11, for discussions. -Kamran


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.

Joshdwb7

If you love what you are doing, there are many ways to make great discoveries and move "up". You could do well as an undergraduate, do internships at exciting places and apply for grad school at a great university.


This will not be a popular question, the idea that the universe was created has long been mocked and "disproven" the further the evolution theory has been taught. They say the universe began as a result of the Big Bang, my question what do you believe caused the Big Bang? It was simply a accident that resulted in the universe we live in now? I understand the idea of believing in a God is too far fetched and out of most people's reasoning, but it is too far fetched to believe that there is a Celestial being or Being's that caused the Bang that created universe or created solar systems in the universe? I find the complexity and the vast context of the universe is too magnificent to be a result of anything but a intention design, what are your thoughts on the origin of the universe and how it came to be?

J-POOL

I think you have to postulate a principle that causes existence. You can call this principle "God". I do call it God.


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?

demilitarized_zone


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