Marcus Feldman in his office at Stanford University, CA

Jason Henry for Quanta Magazine

Marcus Feldman never planned to end up on the front lines of evolutionary biology. “I always wanted to do mathematics, as much as I could,” he said. “There was a little bit of time when I flirted with the idea of being a psychiatrist.”

More than anything else, Feldman is a polymath. His desk at Stanford University, where he has been a professor for 46 years, is tiled with stacks upon stacks of journal articles, most teetering above coffee-cup height. Each stack is dedicated to a topic somehow related to his work in evolutionary theory: the origins of behavioral disorders, the epidemiology of tuberculosis, the way modern humans overrode Neanderthals.

Feldman’s openness to unexpected lines of thinking has allowed him to carve out a contrarian niche in a field where established ideas typically rule the day. Along with a group of similarly unorthodox colleagues, Feldman has developed a proposal called the extended evolutionary synthesis (EES). The EES argues that while the existing framework of evolutionary theory, known as the “modern synthesis,” is basically solid, it needs to be expanded to account for newly recognized drivers of evolution. One such driver is epigenetics — gene-expression changes that stem from exposure to, say, pesticides. While these epigenetic changes are not encoded in an organism’s genes, they do give rise to physical and behavioral differences that natural selection can act upon.

The EES also stresses the importance of culture and behavior in evolution. When prairie dogs construct burrows, for instance, selection pressures may begin to favor behaviors like burrow guarding to keep predators out. And both humans and animals direct their evolution through the social and cultural environments they construct for themselves — a phenomenon Feldman thinks is not well reflected in the modern synthesis.

Quanta Magazine spoke with Feldman at Stanford about how mathematical models can illuminate evolution, his contributions to the extended evolutionary synthesis, and his role in redressing China’s sex-ratio imbalance. An edited and condensed version of the conversation follows.

Jason Henry for Quanta Magazine

Marcus Feldman has been on the faculty at Stanford University since 1971.

QUANTA MAGAZINE: When you were a young man in Australia, would you ever have pictured your career unfolding the way it has?

MARCUS FELDMAN: No! I went to work in Melbourne when IBM opened its offices. I didn’t like working for IBM, so I tried to do a master’s degree in mathematics and statistics at Monash University, which of course involved an enormous cut in pay. I was lucky that my adviser had just come back from America. He introduced me to using mathematics on genetics problems. I had never done a biology course in my life, but I started to work on this class of problems.

The first two years of my Ph.D. at Stanford, I still hadn’t done any biology. But I got so interested in some of the problems I was working on that I decided I’d better take some courses. I became immersed in the application of mathematics to genetics questions. From then on, it was just trying to formalize in mathematical terms the kinds of questions that biologists would ask.

You joined Stanford’s biology department as a faculty member in 1971. What happened after that?

Very soon after my arrival, I met a famous geneticist, Luigi Luca Cavalli-Sforza. He is what I call the consummate Renaissance man. He was interested in the statistics of human genetic and cultural variation — why different people in different parts of the world behave differently, have different rules in their societies and were genetically different from one another. He and I immediately hit it off.

The first thing we did was develop mathematical models to describe cultural differences. What would happen to the old style of genetic evolution if there were also cultural factors that influenced what was happening to the genes in the populations? For example, IQ — if there happened to be genetic contributions to IQ, but also culturally determined contributions to IQ, how would you combine the two of them in a dynamic system?

How do these models reveal how evolution takes place?

One of the nice things about models is you can ask what conditions have to change to make the results change. As Murray Gell-Mann says, models are prostheses for the imagination. They help you think about ways in which you might interpret data, even complicated data.

If you think about use of milk, dairy in itself is culturally transmitted. But there’s a gene called the lactase persistence gene, which allows some people to digest milk. Suppose that people who drink milk get enough extra protein that they can survive better. If those same people are learning from somebody to use cows for the purpose of getting milk, any gene which allows you to drink more milk without getting sick is going to have an advantage in the situation where cows are used for milking.

Jason Henry for Quanta Magazine

Feldman in his office at Stanford.

If the cows weren’t there, that gene wouldn’t have any advantage at all. Using the cows for milk production is not part of your genetics; it’s part of your culture. The spread of that culture had the effect of spreading the lactase persistence gene.

Other cultural things have huge effects on other organisms, not just on us. I’m thinking of the period when everybody was using antibiotics — you took the kid to the doctor, you had a sore throat, you would get an antibiotic. We humans have had a huge effect on the growth of antibiotic resistance. It’s a straightforward predictable consequence of evolution. If there are resistant genes there, they’ll succeed.

Did culture alter humans’ evolutionary course in the distant past, too?

We can construct a model for the movement of modern humans out of Africa into Eurasia and the competition that they’re going to have with the Neanderthals who were already there. We formulated it like a diffusion. You have these people diffusing across the continent, and within the population is a level of culture that could be more advanced than that of the residents. The question we came up with is: Could a smaller population with a lot of culture overcome a bigger population that didn’t have very much culture?

We found that a smaller number of people could invade a population that’s quite a lot bigger if they had a sufficiently developed culture. The way in which the populations grew depended on the level of culture. That group that had the most culture — the modern humans — would be the winner.

In your view, what are some of the shortcomings of the classical model of evolution — the so-called “modern synthesis”?

The modern synthesis developed in the 1930s and 1940s and basically had finished by the 1950s. At that time, little was known about the molecular biology of development — how what’s going on in the development process itself influences what can happen to the evolutionary trajectory of cells and organisms. Although some of its originators were interested in behavior, many were steeped in the eugenics tradition. They would have thought that the majority of behaviors were determined by genes. The inclusion of other forms of inheritance totally changes evolutionary dynamics.

What was your involvement in the early stages of the EES?

My colleagues and I started to build the first quantitative models for “niche construction,” which is an idea that had been around, but peripherally, from writings of the evolutionary biologist Richard Lewontin. What Lewontin had proposed was that individuals don’t only react to their environments, they actually contribute to making them. Rather than solving problems, they construct the environment, which they then have to exist in, and their offspring have to exist in the environment that they changed. Humans do it all the time, but other organisms do it too. The classic example is dams made by beavers; it changes the environment for everything around. You have beavers having offspring that are going to live in the dams their parents and grandparents built. It can affect the behavior of the subsequent generations.

Jason Henry for Quanta Magazine

Video: Feldman explains how he models the effects of a cultural preference — in this case, a preference for sons over daughters in China.

And some of those environmental changes might affect which traits confer fitness, then?

Yes, exactly. After we had written a book on niche construction, I started to think about how the cultural evolution work and the niche construction work would interact. When you’re a scientist and you work on a lot of different things, you can’t separate them — the thoughts cross over. It made it natural to think this was an extension of the evolutionary synthesis.

In a commentary in Nature, you and your co-authors wrote, “We hold that organisms are constructed in development, not simply ‘programmed’ to develop by genes.” What does “constructed in development” mean?

It means there’s an interaction between the subject and the environment. The idea of a genetic blueprint is not tenable in light of all that is now known about how all sorts of environmental contingencies affect traits. For many animals it’s like that. Even plants — the same plant that is genetically identical, if you put it in this environment, it’s going to look totally different from if you put it in that environment.

We now have a better picture of the regulatory process on genes. Epigenetics changes the landscape in genetics because it’s not only the pure DNA sequence which influences what’s going on at the level of proteins and enzymes. There’s this whole other stuff, the other 95 percent of the genome, that acts like rheostats — you slide this thing up and down, you get more or less of this protein. It’s a critical thing in how much of this protein is going to be made. It’s interesting to think about the way in which cultural phenomena, which we used to think were things by themselves, can have this effect on how much messenger RNA is made, and therefore on many aspects of gene regulation.

How can these epigenetic changes affect the traits that natural selection can act on — and therefore the future course of evolution?

We’ve just submitted a paper on epigenetic contributions to longevity in hunter-gatherers. There is increasing evidence of important associations between the level of methylation [which affects how strongly your genes are expressed] and features of your environment such as diet, stress and poverty.

If those things are culturally transmitted, those effects on evolution are going to be longer term. Simple notions of the ways in which traits are formed are going to be thrown out the window.

Jason Henry for Quanta Magazine

Feldman’s bookshelves.

The EES has gotten pushback from many biologists who think that things like cultural evolution and niche construction are already accounted for in evolutionary theory, and that therefore the EES is unnecessary. How do you respond?

I don’t think they are accounted for. You can’t predict, using old theory, what the influence of these newly important phenomena are likely to be on evolution. They don’t fit the framework of all the models that were used to make those original predictions.

People who make models like I do for a living don’t actually believe they’re describing reality. We aren’t saying that our model is more probable than another model; we’re saying it exposes what is possible. The EES includes more of these phenomena, that now we have a better handle on biologically, in thinking about evolution.

You’ve been looking into the imbalance in the sex ratio in China and the potential long-term consequences that imbalance could have. How has your background in evolution and modeling informed that research?

The first paper we wrote on that was really about genetics. The idea was to use the standard idea of sex determined by sex chromosomes — XX for female and XY for males — and to ask what would happen if culture affected the different numbers of each being produced. One of my colleagues in China saw this stuff. He said, “Let’s talk about son preference in the sex ratio.” So we started to make models for a cultural preference for sons, a preference that could be learned and hence transmitted. We made models where a given couple would decide they would prefer to have sons, and they would pass on that preference to their children.

What we were able to do was to make a projection of what would happen in China if they continued on this path. We really were able to get a lot of stuff published, some things that might have influenced government policy. The government finally woke up and saw that not only was it having a bad effect on females, but it was going to affect the economy because the number of marriages was going down. You have these 30, 40 million men who can’t find wives and the long-term outlook for the labor market and social security was not promising.

How do you think the EES will change the direction of biology research?

I think it’s a bit hard to tell yet. We still have — I’m going to put on my mathematical hat — very few models for how development and evolution interact. They’re based in models from the 1920s. That needs to change, in my view. We have very few models that integrate gene regulation and genic evolution; they’re really quite limited in scope.

I’m always excited about the subject getting more complex. It means there’s more and more room for the people who are well-trained quantitatively. It’s a bit selfish, but there you are.

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  • Some of the erroneous claims from a fringe universally panned within biology:

    – A fringe which has no result is among the "front lines".
    – Evolutionary biology which is massively expanding in scope needs to be expanded.
    – Epigenetics which is driven by evolution needs to be recognized as a driver.
    – The importance of culture and behavior as extended phenotype is not "well" reflected by evolutionary biology.
    – The 2nd OOA migration with "a lot of culture" into Europe among at the time equally culturally advanced Neanderthals met a population with less culture.
    – Evolutionary biology which has long massively adopted advanced genetic methods didn't adopt them.
    – Epigenetics effects which dies out within 2-3 generation has effects in the "longer term".
    – EES that hasn't published any useful results has exposed "what is possible".
    – Evolutionary developmental biology which took off in the 70s didn't change since the 20s.

    Evolutionary biologist Jerry Coyne is my go-to source here:

    "Let me say first that I’m a bit puzzled by the continual appearance of these “Does evolution need a revolution?” pieces. If our field really was undergoing a revolution, we wouldn’t have to debate it."

    "That aside, let me discuss briefly the new phenomena that, the “yes” authors say, call for a new paradigm, an overthrow of what they call “standard evolutionary theory” (SET)."

    "1. The evolution of development (“evo devo”). … There is still no good empirical evidence for “convergence” due to similarity of developmental pathways that are constrained."

    "2. Developmental plasticity. … the important thing to recognize is that behavioral change and its sequelae (like all the other adaptations for living on land) cannot evolve unless those changes have a genetic basis."

    "3. “Nongenetic” forms of evolution. … Cultural evolution is not genetic evolution, and hence not part of the SET, which rests on changes in genes. … The problem with [epigenetics] is that such cases of environmental changes in DNA are always temporary, for they’re not coded in the DNA and thus cannot persist forever. And if they’re temporary, they cannot cause long-term adaptive evolution.

    "4. “Niche construction.” … While this idea is getting new attention, and deservedly so, it doesn’t call for a revolution in SET. First of all, it’s not particularly new. The idea of “gene-culture” coevolution [which Jerry separates out from cultural evolution mentioned earlier] has been around a long time."

    "That is not to disparage this phenomenon—or any of these phenomena. Niche construction seems more likely to be important than “genes follow phenotype” plasticity, or than adaptive epigenetic evolution, of which we have not a single example. All these ideas deserve empirical study. But none call for a new paradigm."

    [ ]

    But two years later Jerry also says this:

    "I want to end by putting up Welch’s explanation for why these persistent calls for reform are harmful:

    "If criticism of evolutionary biology is inevitable, why grouse about it? It is easy to habituate to misleading alarm calls (Cheney and Seyfarth 1988), and churlish to complain about peripheral ideas, which, by definition, have little influence on what most scientists do. However, claims that evolutionary biology is misguided or importantly incomplete are not harmless, but actively hinder progress in the field. Indeed, they do so in several ways. First, the claims misrepresent the field to the wider public. It is unfair to use guilt by association—many fine studies are cited on creationist websites—but a field that urgently needs reform is a field “in crisis” (Mazur 2010), and when it fails to reform, this lends credibility to claims that scientists are, at best, hidebound and foolish, and at worst, guilty of ideologically-motivated deception (Mazur 2010; Teresi 2011). Such claims find an eager audience among those who reject the scientific consensus on other grounds. For example, Fodor and Piattelli-Palmarini (2010) present a priori objections to (their version of) natural selection, but also include a fairly typical laundry list to add some empirical heft. Chorost (2013) criticized Nagel (2012) for not including a laundry list. Second, and within the field, the claims encourage neophilia. This makes us unwilling to build on previous work, to integrate new findings and ideas with existing explanatory frameworks, to replicate published results (Nakagawa and Parker 2015), or to solve the field’s many outstanding problems (Maynard Smith 1977; John 1981). It also distracts attention from the ways in which all biologists can do something genuinely new, such as expanding the range of study organisms. The comparative method (Maynard Smith and Halliday 1979), Krogh’s principle (Krebs 1975), and our ignorance of biodiversity (Nee 2004), all suggest that this is one way that we might usefully extend the field.""

    [ ]

    That last bit talks to me, as I started to study for a MSc in Bioinformatics this autumn. Luckily I had these fringe areas sorted out before that!

  • So "individuals don’t only react to their environments, they actually contribute to making them. Rather than solving problems, they construct the environment, which they then have to exist in, and their offspring have to exist in the environment that they changed. Humans do it all the time, but other organisms do it too. The classic example is dams made by beavers; it changes the environment for everything around. You have beavers having offspring that are going to live in the dams their parents and grandparents built. It can affect the behavior of the subsequent generations."

    Well here is another "go-to source." Here are the "extracorporaneous limbs" (or "extended phenotype") of Samuel Butler (1865): "Men are not merely the children of their parents, but they are begotten of the institutions of the state of the mechanical sciences under which they are born and bred. These things have made us what we are. We are children of the plough, the spade, the ship, we are children of the extended liberty and knowledge which the printing press has diffused. Our ancestors added these things to their previously existing members; the new limbs were preserved by natural selection and incorporated into human society; they descended with modifications, and hence proceeds the difference between our ancestors and ourselves."

  • Isn't niche construction and occupation the basis for mammalian evolution to begin with. The supposed flexibility of mammals as opposed to reptiles in niche occupation at the end of the Cretaceous resulted in the explosion of mammalian diversity.

  • Not being in the field, I'm a bit confused, but fascinated.

    As I understand it (please correct me) there is no disagreement about whether non-DNA-sequence based inheritance occurs. The question is whether a different mutation model is required to account for those epigenetically inherited traits?

    This seems like a question which one might address computationally.

  • "The classic example is dams made by beavers; it changes the environment for everything around. You have beavers having offspring that are going to live in the dams their parents and grandparents built. It can affect the behavior of the subsequent generations."

    This statement makes very little sense to me. Beavers have a repertoire of behaviors, fixed action patterns, presumably encoded in neural circuits, such as building dams and lodges, I’m guessing they may even learn to become better builders from their parents, I don’t know. Perhaps one particular beaver is a slightly better builder than another, will his offspring have more fitness because of their acquired superior “knowledge” of dam building? Or will that parent beaver leave more offspring and copies of his genes increasing his own fitness because of his superior abilities?

    Perhaps, a particular beaver is an OK lodge builder but has a great sense of style, adding columns or some some other decorative touch to the lodge that will awe his offspring who then imitate dad’s eccentric style. This style spreads and only beavers in a local geographic location create lodges with columns, hence creating a local beaver culture. This sort of thing has been documented with apes and monkeys but not beavers to my knowledge.

    Dams or lodges affect the behavior of subsequent generations of beavers in what way? The genes that encode for the behaviors of dams and lodges are adapted for an environment with trees and water. The beaver brain needs inputs from the environment, I am guessing, such as trees and water to create outputs of dams and lodges. Years ago, someone had the bright idea of introducing beavers to Tierra del Fuego; without any natural predators they denuded the landscape of trees. The beavers made changes to the environment without question but I doubt any changes where made to beaver brains, at least in the short term.

    What form of inheritance is professor Feldman talking about that “totally changes evolutionary dynamics” in beavers, to say nothing of humans?

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