Explaining Behavior 13: NeoDarwinian Theory

Every environment selects for something

This is part of a series on how to explain human behavior. It is based on a course developed by the late Donald Black at the University of Virginia. Parts 1 through 6 discussed the general logic of scientific theory. From Part 7 onward we cover different strategies or paradigms for developing explanations. The last installment was Part 12: Conflict Theory.

FYI, this installment departs the most from what I learned from Donald and contains relatively more of my own ideas. I’ve been interested in evolution since high school, and The Selfish Gene sits next to Black’s Moral Time as one of the prized signed books on my shelf.

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If you’re familiar with homicide cases, you know the pattern. Guy A does some trivial thing to offend Guy B — calls him a name, eyeballs his woman, shows up to a house party uninvited, whatever. Tempers flare, chests puff out, and next thing you know there’s a fatal shooting or stabbing or beating.

Why kill over something so trivial? The core issue is respect. Honor. Reputation. Manliness. Not being dominated, not being humiliated, showing everyone who’s boss.

It's almost always men. Women rarely kill at all, and even more rarely kill one another.

Why should young men be so prone to this sort of conflict? Why be so sensitive to disrespect that you escalate a trivial disagreement into a lethal violence?

Psychologists Margo Wilson and Martin Daly say the first step in answering the question is to recognize that the pattern isn’t limited to human beings:

Dangerous, confrontational competition among males is not unique to our species. Violent conflict with attendant mortality risk is widespread in the animal kingdom, and it is usually a male affair. To the evolutionist, such ubiquitous behavioral inclinations demand explanation in terms of their adaptive functions for the actors….

In other words, the commonality of the pattern across species suggests that it’s an adaptation to pass along one’s genes. And something makes it a better adaptation for males than for females.

The key difference, Wilson and Daly say, is variance in reproductive success.

Variance is low when all individuals in a population have around the same number of offspring. It is high when some have a lot more than others. The more variance there is, the higher the stakes of competition for any resources that might help one wind up on the high end rather than the low one. The higher the stakes, the greater the reward for taking big risks in order to win. So the more variance, the more a tendency to aggressively compete, even at great danger to oneself, gets passed down the generations: Each generation, a disproportionate number of offspring are the descendants of the bold risk-takers who climbed to the top of the heap in the prior generation.

In most mammals and all primates, males have higher fitness variance. The reason is that males invest less in their offspring — It’s the female who carries babies inside her and nurses them after they’re born. She can only get pregnant once a mating season, maybe even once every few years. But males can potentially impregnate many different females in the same timespan. This raises variance at the top end: The most successful male can have ten times the offspring of the most successful female. It also raises variance at the bottom end: The more males who have multiple mates, the more who have zero mates, and so having no offspring at all is also more common among males than among females.

If you want to see the human version, here’s the Wikipedia lists for people with the most children. Notice that there’s one list for women and another for men. The male list goes far higher and includes sultans and conquerors who were taking wives and concubines from the men they were killing or enslaving.

So for males, fitness variance is higher. Competition for mates is higher stakes, closer to winner take all. This explains why males are more inclined to fight each other over females than females are to fight over males. And, by extension, it explains why males are more likely to fight over whatever gets them females, such as a territory or a position in the social hierarchy.

This explains what we see in rams, stags, tomcats, and gorillas. And it also explains why men are more likely than women to chimp out when someone puts them down.

Wilson and Daly’s explanation of “young male syndrome” is an example of NeoDarwinism in social science.

NeoDarwinian theories, as Donald Black defined them, explain behavior with selection by the environment. NeoDarwinism is the dominant paradigm in modern biology and also gets applied in the social sciences under names like sociobiology and evolutionary psychology. NeoDarwinism in this sense is a broad strategy of explanation, used in various theories of various subjects. But as the name implies, it has its roots in Charles Darwin’s theory of evolution by natural selection. We can better understand NeoDarwinian social science by first understanding Darwin’s theory.

Explaining Evolution

By the late 1700s, there was already much evidence from geology and paleontology that lifeforms on earth had changed over time. There were animals in the fossil record that did not look like animals today. But why?

Some explained this with catastrophic events — whether the great Biblical flood or something more naturalistic — that wiped out past lifeforms and perhaps occasioned the creation of new ones.

In 1809, Jean Baptiste Lamarck, tried to account for evidence that not only did different sorts of lifeforms exist across Earth’s history, but that living ones showed evidence of having changed from their ancestors in ways that made them better suited to their environments. He pointed, for example, to vestigial traits, such as the blind eyes of mole rats.

His explanation for this evolution was that organisms can alter their own bodies through use and disuse of different parts — the example in my high school biology textbook was giraffes stretching their necks to reach the leaves in trees. They then pass on these modifications to their offspring, who in turn do the same, and so on down the generations. Thus organisms become adapted to different niches, and eventually are different kinds of organisms altogether.

Lamarck deserves more credit than he often gets for developing a falsifiable theory of evolution. The problem is that it has indeed been falsified: Exaggerated claims about epigenetics aside, there isn’t any mechanism for passing on acquired traits. Getting jacked at the gym won’t make your descendants more muscular.

Enter Charles Darwin and Alfred Russel Wallace. They both independently hit upon the same explanation — natural selection — and coauthored a paper presenting it to the world. But Darwin was working on the idea first and gave the more thorough treatment in his book, The Origin of Species, so he usually gets the credit. The theory of natural selection rests on four principles:

1. Variation. In any population, there will be at least slight variations in traits like speed, coloration, aggressiveness, and so forth. Unlike Lamarck’s theory that variation is induced by effort, in Darwin’s theory it’s blind — maybe not truly statistically random, but not purposive.

2. Heredity. Organisms pass along their traits to offspring. Taller individuals tend to have taller young, and so forth.

3. Differential Survival. Not all individuals are equally likely to survive, or at least to survive long enough to reproduce. Differential survival is non-random — some variations are more likely than others to make it.

4. Selective Retention. This is really just an implication of #2 plus #3: Some variations tend to get retained in the population over time, while others tend to get weeded out.

The logical implication of all this is that the average traits of a population will change over time. Multiply across geologic timescales and a wide range of environments, and you get the divergence of organisms in many distinct species, all adapted to different niches.

Let me emphasize that evolution in the broad the broad sense of change over time really is a logical implication of the principles above: If you have those factors in place, the population must be changing. How could it be otherwise?

This led philosopher Karl Popper to question whether Darwin’s theory is actually falsifiable in the same way as, say, Newton’s law of gravitation, or whether it is something closer to a logical truth.

The principles themselves can be taken as falsifiable empirical claims — it’s logically possible to have a population of identical individuals with no variation, or variation (including acquired characteristics) that’s not heritable. It’s just that casual observation shows that organisms do vary, and most traits are heritable.

Everyone already knew that. Darwin’s genius lay not in seeing that parents resemble children, or that the slow gazelle gets caught by the cheetah. It lay in thinking through the relationship and implications of these readily observable facts in the face of inhumanly long stretches of time. It was a feat of both logic and imagination.

The core idea of natural selection may not actually be an empirical proposition in the sense we’ve discussed in this series. And by itself, it doesn’t predict when evolution will take this direction or that. But it is a crucial part of such theories — a theoretical tool that allows us to explain the structure and function of organisms, and patterns in how they change over time.

Bringing in the Genes

Why add the prefix “neo” to Darwinian theory? Darwin and Wallace came up with the theory of natural section a time when no one — other than a monk breeding pea plants — knew anything about the mechanisms behind variation and heredity. They could see that these things existed, but they didn’t know exactly how they worked.

But by the mid-twentieth century, the fields of genetics was up and running. We now know that variation in traits comes from variation in strands of DNA, a self-replicating molecule that contains a sort of code that each organism runs as it grows and behaves. What we usually call genes are sections of the DNA strands that code for a particular trait. These genes get replicated when organisms reproduce, and offspring inherit genes from their parents, explaining the heredity of traits. Replication isn’t perfect, and copying errors called mutations introduce new variation. The mixing of genes during reproduction — you get half from Dad, half from Mom — also introduces variation.

The new knowledge did more than explain the mechanisms behind variation and heredity. Taking account of genes led to extensions and refinements to the theory of natural selection. The result is neoDarwinism, or what biologists often call the modern synthesis of classical Darwinism and genetics.

One new idea has to do with the unit of selection. People often think about natural selection acting on the individual organism — after all, it is the individual gazelle that is either fast enough to escape the cheetah or gets selected out for being too slow. But modern evolutionary theory recognizes that selection happens at other levels as well, including at the level of the gene itself.

Consider: If it’s a particular gene that makes the gazelle run slower, it’s at least as accurate to say that gene got selected out when the cheetah caught his supper. Vice versa, a gene that makes the gazelle faster is a gene that’s going to avoid having its host eaten, and so is likely to wind up getting copied into baby gazelles. Over the generations, more and more gazelles will be walking around with this gene inside them, and fewer and fewer will be walking around with the slowpoke gene. We can thus think of evolution as changes in the frequencies of different genes in a gene pool, and of genes as being selected based on how good they are at getting themselves spread down the generations.

Only helping to escape a predator isn’t the only way a gene might be good at getting itself copied. Maybe a different gene makes its host look super attractive to the opposite sex, with flashy colors or a big tail. These things might make the individual more likely to get eaten by a predator, but as long as the heightened attractiveness meant the gene gets passed along into some babies first, it’s a good deal for the gene.

When you think about it, a lot of things might be good deals for the gene but bad deals for the individual that carries it.

In his book The Selfish Gene, biologist Richard Dawkins advocated a “genes-eye” view of evolution. The title refers to the notion that gene itself is “selfish” — in the sense that natural selection will encourage genes good at getting themselves copied, regardless of whether that’s good for the individual as such. The individual organism is a disposable vehicle — “a survival machine.”

Why doesn’t evolution stop us from aging and dying? Like an old car, there’s a point where you’re not worth the cost of maintenance. And the gene that gives you terminal cancer at age 65 is no less fit than any of the others you’re carrying — after all, by that age, you’ve probably already had children, and the gene is already copied into the next generation. What does it care if you wanted another twenty years?

Thinking of genes as units of selection helps explain other puzzles. For instance, consider that some animals act altruistically, giving up resources or risking injury to help others of their kind. Given that this would detract from the altruistic individual’s chances of surviving and reproducing, we need to explain why natural selection didn’t weed out such a tendency.

One explanation is kin-selection theory. Kin share DNA. About half of your genes are copies of your Dad’s, and the other half are copies of your Mom’s, so you share about 50% of your genes with each parent. And since that’s true of your siblings as well, on average they have about half the same genes as you do. Your first cousins have the same grandparents but not the same parents, so they share less — about 13%. And so on and so forth, with shared genes declining as the kin gets more genealogically distant.

One upshot of this is that if you have a gene that inclines you to look out for close kin, your close kin likely have a copy of that gene as well. So it’s effectively a gene that looks out for itself. Even if the altruistic inclination, on average, slightly reduces the reproductive success of whoever carries it, it can make up for it with a corresponding increase in the reproductive success of that individual’s close kin.

One can actually do the math on how much an altruistic gene needs to help varying degrees of kin in order to break even or come out ahead on a given reduction in the success of its host. Hence biologist J.B.S. Haldane’s joke: "I would lay down my life for two brothers or eight cousins.”

NeoDarwinian Conceptual Theory

Given that this paradigm explains behavior with selection by the environment, both selection and environment are important concepts.

Environment is extremely broad and includes not just physical conditions like terrain and weather, but all the other organisms the individual might interact with, including predators, prey, rivals, allies, and potential mates. If we’re looking at it from the gene’s point of view, it includes the other genes in the gene pool, or maybe even other genes in the same organism — how successful a gene is can depend on what other genes it finds itself next to on the DNA strand.

Note that since the environment includes other organisms, evolution itself constantly changes the environment. Hence biologists talk about coevolution, in which there’s a reciprocal influence between the evolution of one species and another. One example is the evolutionary arms-race between predators and prey.

Selection means that something affects the odds of a trait getting passed on. As long as survival and reproduction are nonrandom, selection is occurring. Every environment selects for something. But different aspects of the environment might select for different things, producing various selection pressures.

Evolutionary theorists might classify different kinds of selection pressure. Sexual selection, for example, is when the mate preferences of one sex selects for certain traits in the opposite sex. The classic example is that if peahens only mate with the peacock who has the biggest tail, then over the generations, peacocks develop huge tails.

Note that a trait can be selected out of a population without the individual organism being selected out. A trait that makes an organism uninterested in mating doesn’t necessarily make it die sooner — it might even outlive its fellows who are out fighting over mates! But the trait itself, and the genes that encourage it, are not going to proliferate for long.

For that matter, a trait might leave a breeding population through selective outmigration: If the boldest members all go over the mountain and never come back, in a few generations your average member will be less bold — even if the bold ones are doing just fine over on the other side.

People still often describe natural selection as a matter of “survival of the fittest,” a phrase coined by English sociologist Herbert Spencer. But in modern evolutionary theory, fitness means reproductive success. So evolutionary fitness is not to be confused with the kind of fitness you pursue at the gym: If being slow, dumb, and fat leads to more babies, then slow, dumb, and fat are fit.

(Yes, this is the premise of the film Idiocracy.)

Because of kin selection, modern biologists use the concept of inclusive fitness to refer to reproductive success of the individual, plus the reproductive success of its kin, weighted by how much DNA they share.

NeoDarwinian Social Science

So how does evolutionary thinking help us explain human behavior?

I classify four kinds of neoDarwinian social science. The first two are biological in that they’re concerned with the human organism and ultimately their explanations hinge on differences in inclusive fitness. The first approach is to look at how the biological evolution of the human species shapes our social behavior, while the second considers how human society and culture has shaped our biological evolution. The next two are non-biological in the sense that they extend the logic of selection beyond the human organism as such, and the kinds of evolution they posit don’t require changes in gene frequencies. One is concerned with populations of organizations, the other with the evolution of culture.

1. How Biological Evolution Explains Society

Looking at how biologically evolved tendencies shape social behavior is the main activity of what is often called evolutionary psychology and sociobiology (the latter term popularized by E.O. Wilson through his book Sociobiology: A New Synthesis). Work in this vein applies modern evolutionary theory to the social behaviors of humans and other group-welling animals. People are organisms, and we can explain human behavior with instincts and proclivities honed by natural selection.

Wilson and Daly’s work on “Young Male Syndrome” is one example, explaining why this particular demographic is prone to competitive risk-taking and going to the mat to avoid a loss of face. The two psychologists also propose that this tendency is sensitive to context, becoming more pronounced in stratified societies or in encounters in front of audiences.

In their book Homicide: Foundations of Human Behavior, they propose explanations for other patterns of lethal violence. A major idea is a corollary of kin selection theory that I would summarize as: homicide varies directly with genetic distance.

A well-known pattern is that children are at far higher risk of being killed by stepparents than by their genetic parents. Daly and Wilson argue that this makes perfect evolutionary sense — in terms of increasing inclusive fitness, putting effort into raising someone else’s kids is a bad investment.

And they argue that other sorts of child-killing also happen in circumstances where the child is a bad evolutionary investment. Cross-culturally and historically, birth defects are a common reason for infanticide, as are resource constraints — in some cultures its common practice to kill one of a pair of twins, or to kill a baby born before an older sibling is weaned. And in some times and places, suspected cuckoldry is a common, maybe even socially acceptable reason for a man to kill his wife’s child.

In my experience in the classroom these kinds of explanations provoke a lot of hostility — sociology students often seem to dislike neoDarwinism as much as they like neoMarxism.

I suspect at least part of it is a variety of naturalistic fallacy, whereby if you explain a pattern of human conduct — especially bad conduct like murder — as the result of biological instincts, people assume that you’re trying to justify it.

Or perhaps they think that pointing out evolutionary roots of behaviors means they cannot be changed at all. For it seems another source of consternation with evolutionary explanation is the false dilemma that if cultural and social factors shape behavior, then biology cannot. This crops up in sociological discussions of sex differences.

Sociologists like to focus on how gender roles are socially constructed and gendered behavior is socially learned. And it’s certainly true that we can see variation across culture and history in exactly how men and women are expected to dress and act. But it’s just as true that this cultural variation in gender is overlaid on biological variation in sex, and that biological differences can shape cultural ones.

Sociologist and demographer J. Richard Udry has done some interesting work in this regard. In an article “The Biological Limits of Gender Construction,” he writes:

My primary hypothesis is that the effect on women of their childhood gender socialization is constrained by the biological process that produces natural behavior predispositions. This extension is stimulated by and modeled after parallel experimental work on primates and humans

He goes on to explain the developmental role of hormones, especially testosterone, in creating sex-typical behavior. He posits that prenatal testosterone exposure in females can shape how they respond to gender socialization: It help explain the difference between a girly girl and a tomboy. Using data from a study that started with pregnant women a generation prior, he found that testosterone exposure in the womb predicted woman’s gendered behavior 30 years later, as measured by their interests, occupation, personality, and how feminine they appeared to others.

2. How Society Explains Biological Evolution

If we’re talking about how selection by the environment shapes the human organism, we have to consider that this environment includes the society people live in — technology, culture, government, settlement patterns, and all the rest of it.

In the 10,000 Year Explosion, Greg Cochrane and Henry Harpending posit that the advent of farming and civilization would have created strong and novel selection pressures on the human species.

Consider the difference between the small, sparse, and mobile populations typical of forager societies and the big, dense, and sedentary populations of civilizations. The shift from one to another has certainly affected the evolution of germs. Epidemic diseases like smallpox, measles, and influenza simply didn’t exist prior to civilization, for there wasn’t enough population to support them. Crowding together large numbers of people and animals led to the evolution of highly virulent diseases that can afford to kill their hosts because there are always fresh ones available.

The novel disease environment then put new selection pressure on humans: Civilized people faced far stronger selection pressure to develop immune systems capable of dealing with virulent epidemic diseases. The result is an evolutionary arms race between people and germs that explains why when Europeans showed up in the Americas, it was the Native Americans getting devasted by European germs rather than the reverse.

Other plausible effects of civilization include those of the domestication of dairy animals, which would change the evolutionary payoff being able to digest milk as an adult (something most mammals and most humans can’t do very well) or changes in personality and intelligence — are the same mental traits really optimal for foragers, farmers, or entire breeding populations specialized in business and finance?

Patterns of social interaction might be what originally drove the evolution of human intelligence. The social intelligence hypothesis (also called social brain hypothesis or Machiavellian intelligence hypothesis) proposes that the complexity of animal social groups creates a selection pressure for greater intelligence. Advanced by figures like primatologist Frans de Waal and anthropologist Robin Dunbar, the idea is that in group-dwelling animals where members can variously cooperate or compete, there’s a lot of advantage in being able to keep track of individuals, relationships, and circumstances — to distinguish friend from foe, kin from non-kin, different ranks in the social hierarchy, and times to be selfish from times to share. The more complex the social group, the more brainpower ones needs to do this, and so the more that natural selection tends to favor smarts.

There’s some support for the idea that animals dwelling in these sort of social groups — including primates and dolphins — tend to have larger brains relative to their body size and be more intelligent than solitary animals.

More intelligence allows for more social complexity, which can in turn select for further intelligence. If this feedback cycle runs long enough, you get humanity. We didn’t evolve these brains to outsmart the lions; we evolved them to outsmart one another.

But it’s not just smarts that make humans different. In his book Moral Origins, anthropologist Christopher Boehm argues that humans are a distinctly moral animal: We have a capacity for empathy that lets us adhere to the Golden Rule, and a capacity to internalize social rules and to feel genuine emotional distress when we deviate from them. Blushing with shame, for instance, is an automatic physiological reaction that shows how hard-wired people are to conform to social norms and group morality.

Boehm argues that these capacities have their evolutionary origin in early human groups policing bullies and freeriders. By killing or exiling those who were selfish and uncooperative, our ancestors put a strong selection pressure on developing psychological characteristics like the capacity for empathy, shame, guilt, and generalized altruism. Our conscience is the result of social selection, and human are gentler than chimpanzees because we’ve effectively domesticated one another.

3. The Population Ecology of Organizations

Though it was pioneered in the study of biology, there’s no necessary reason that aspects of neoDarwinism — including the general strategy of explaining with selection by the environment — can’t be extended beyond organisms as such.

Consider organizations. While composed of people, they can be born and die within the lifetime of their members or can live on for many human generations. They might even reproduce after a fashion, founding new chapters or spinning off subsidiaries.

In a 1977 article “The Population Ecology of Organizations,” Michael T. Hannan and John Freeman argued that the study of organizations suffered from a dearth of selectionist thinking.

The primary way of explaining the structure and function of organizations is to assume that organizational leaders scanned their environment for threats and opportunities and make strategic decisions to adapt their organization to them. And surely this does happen to some degree and explains at least a little of the variation in organizational structure and behavior.

But it can’t explain all of it, or maybe even most of it. For if one looks at how organizations react to their environment, there are oh-so-many constraints on this sort of rational adaptation. These sources of structural inertia include information constraints, internal politics, vested interests in the status quo, legal and fiscal barriers, collective action problems, and investment in existing physical plant, equipment, and specialized personnel. Watch the business world for any period time and you’ll observe many astounding failures of an organization to pivot to new opportunities or adapt to new technologies. Consider, for example, how the Kodak film company completely failed to adapt to the advent of digital cameras.

Given these constraints, if we observe a world in which the large majority of organizations seem very well-adapted to their current environment, it is likely because the ones that aren’t well-adapted tend to rapidly go extinct.

Thus Hannan and Freeman suggest looking at how environmental selection can predict and explain the population of “organizational forms.”

For instance, since different environments select for different organizational forms, anything that homogenizes different local environments will reduce the diversity of forms. The expansion of markets — breaking down the isolation of local markets and integrating them with national ones — has a homogenizing influence. So too does the expansion of federal regulations that affect businesses across all states and localities. The same forms tend to be the most successful forms everywhere, and so the population of organizations homogenizes.

One point I often add is that the success of certain forms itself has a homogenizing influence, since now every local business must compete with the same successful chains. Thus every American town in a certain population range has the Starbucks coffee chain and the aggressively artsy local “not Starbucks” alternative.

You could get to the same prediction with standard rational choice economics, saying that homogeneous environments make for homogeneous incentives and therefore homogeneous decisions. But from the population ecology perspective, traditional economic accounts often underemphasize the “destruction” part of capitalism’s creative destruction. The current distribution of forms is the result of many forms going the way of the dodo. And the pace and patterning of extinction is something else we might predict using a neoDarwinian approach.

If extinction happens when organizations aren’t well-adapted to their environment, the rate of extinction should vary with the pace of environmental change. And in an environment of rapid change, certain forms are favored over others. The basic proposition is that greater environmental instability favors generalists (those with broad niches, like Walmart) over specialists (those with narrow niches, like Blockbuster Video). But as Hannan and Freeman note, the exact prediction will vary based on how rapid and coarse-grained the changes are.

Organizational variation isn’t blind in the same way genetic variation is — founders and executives are trying to adapt. Whether they can actually do so might depend on general properties of the organization that render it more or less adaptable. In another article, Hannan and Freeman posit that organizational size and age affect the structural inertia that inhibits adaptation, and thus might be used to predict extinction rates.

For example, smaller organizations have the least inertia and are more likely to attempt to pivot when the environment shifts. But while larger organizations have more inertia, they also have greater resources that might allow them to plow through a fitness valley and survive a major reorganization. Hannan and Freeman weigh various options and conclude there’s no clear relationship between size and extinction rates. But we might posit a U-curved relationship, in which times of rapid change tends to favor either very large or very small firms, with the population of mid-sized firms shrinking.

4. Theories of Cultural Evolution

Clearly cultural evolution can happen independently of biological evolution — human technology, language, beliefs, change far more quickly than our gene pool. But we still might be able to apply neoDarwinism to understanding how culture evolves.

Consider the way science develops. Psychologist Donald T. Campbell coined the term evolutionary epistemology to refer to the notion that scientific ideas evolve by a process of selection, in which those that best match the evidence survive to be the basis of further revisions and those that least match it are abandoned. Philosopher Karl Popper also advanced this idea, seeing the evolution of science as a cultural extension of how drives and instincts evolved.

According to Popper, the drives and instincts of organisms contain a kind of implicit prototheory of the external world — going toward the dark will bring safety, green things are good to eat, bright colors mean danger, and so forth. These prototheories are constantly tested against the external environment, with the most wrong getting weeded out. Human intelligence and language allows us to creatively devise theories and treat them as objects, letting cultural innovations replace genetic mutations. But when we apply our ideas to practical or scientific problems, we’re still engaged in the process of testing them against the natural world and weeding out those that match it the least.

More influential in popular culture is the chapter in Richard Dawkin’s The Selfish Gene on “Memes: The New Replicators.”

Dawkins begins by asking what is so special about genes, answering “that they are replicators.” Replicators are the basis of cumulative evolution, allowing for differential survival and selective retention. If we find life on some distant world, it might have a totally different biochemistry, with genetic material quite different from DNA — but it will be based on some sort of replicator. But, he writes, we do not have to go to distant worlds to find a replicator that is distinct from our genes.

Dawkins then coins the concept of meme, a unit of culture analogous to the gene:

“Examples of memes are tunes, ideas, catch-phrases, clothes fashions, ways of making pots or of building arches. Just as genes propagate themselves in the gene pool by leaping from body to body via sperm or eggs, so memes propagate themselves in the meme pool by leaping from brain to brain via process which, in the broad sense, can be called imitation. If a scientist hears, or reads about, a good idea, he passed it on to his colleagues and students. He mentions it in his articles and his lectures. If the idea catches on, it can be said to propagate itself, spreading from brain to brain.”

Just as we can understand biological evolution as the changing frequency of genes in the gene pool, we can understand cultural evolution as the changing frequency of memes in the meme pool.

Memes code for various traits — such as knowledge of how to do something, or the belief that one ought to do it — that can be more or less advantageous for getting passed. Sometimes these traits are advantageous to their biological hosts and get passed on because they aid our biological survival. But much as our genes are “selfish,” so are our memes, and what’s good for the meme isn’t necessarily good for either the individual or his genes. A meme that makes its host take a vow of celibacy and dedicate his life to spreading the meme rather than getting distracted by marriage and family might be a very fit meme, even though it extinguishes its host’s genes.

My students are often surprised to learn that this is actually the origin of the word meme. The concept itself is an example of how culture evolves: It wasn’t in widespread usage until the social media age, when people started using it to refer to a particular genre of humorous images-with-text that were widely shared on the web. The shift in meaning from general to specific was a mutation that made the concept more successful, and this mutant strain has spread far more widely than its ancestral form.

The ancestral form did enjoy a brief flurry of attention in some circles. Around the turn of the twenty-first century, there were books like Susan Blackmore’s The Meme Machine and Robert Aunger’s The Electric Meme that tried to carry forward Dawkins’s idea and found and a new science of memetics. There was even a short-lived Journal of Memetics. But the burgeoning field seems to have fizzled out with little progress.

One problem might be too much concern with conceptualizing memes. Discussions tended to revolve around defining units of culture, or asking whether memes were ultimately reducible to discrete physical entities like electrical signals, or elaborating on Dawkins’ concept of memeplex. There was also a lot of metatheoretical discussion of things like meme-gene coevolution.

In this, the subsequent work carried forward the great shortcoming of Dawkins’ chapter, which never much got beyond conceptual theory and metatheory. It lacked propositions. It did not explain variation.

But despite the decline of memetics, scientists continue to study cultural evolution. Joseph Henrich’s The Secret of Our Success is a notable example. I mentioned this work in my post on functionalism, because evolutionary theory provides an explanation for why functionalist accounts are often descriptively correct: Evolution by selection tends to produce traits that help the organism survive, and this appears true for cultural evolution as well.

Henrich makes a powerful case by drawing attention to various survival problems whose solution is complex, causally opaque, and unlikely to have ever been invented by a single individual. For instance, consider the steps involved in preparing manioc, a tuber that will cause cyanide poisoning if not prepared correctly:

“In the Americas, where manioc was first domesticated, societies who relied on bitter varieties for thousands of years show no evidence of chronic cyanide poisoning. In the Columbian Amazon, for example, indigenous Turkanoans use a multistep, multiday processing technique that involves scraping, grating, and finally washing the roots in order to separate the fiber, starch, and liquid. Once prepared, the liquid is boiled into a beverage, but the fiber and starch must sit for two more days, when they can be baked and eaten….

Such processing techniques are crucial…However, despite their utility, one person would have a difficult time figuring out the detoxification technique. Consider the situation from the point of view of the children and adolescents who are learning the techniques. They would have rarely, if ever, seen anyone get cyanide poisoning, because the techniques work. And even if the processing was ineffective, such that cases of goiter (swollen necks) or neurological problems were common, it would still be hard to recognize the link between these chronic health issues and eating manioc. Most people would have been eating manioc for years with no apparent effects…boiling alone is insufficient to prevent chronic conditions for bitter varieties. Boiling does, however, remove or reduce the bitter taste and prevent acute symptoms. So, if one did the common-sense thing and just boiled the high-cyanogenic manioc, everything would seem fine.

Henrich’s answer for how people figured out these techniques is that they didn’t: These and myriad other bits of survival knowledge accumulate gradually down the generations through a process of cultural evolution.

Henrich argues that the capacity for cultural evolution, more than individual intelligence as such, is what allowed human beings to spread to every biome on the planet — a thesis he backs up with numerous examples of European explorers being completely at a loss for how to survive in novel environments.

He leaves the exact process as something of a black box — it’s not clear how exactly a single new step gets added to the manioc process, or through which selection mechanisms it gets retained when its effects on health are individually minor and long-term. But he does propose a theory of what characteristics allow cumulative cultural evolution in humans: our strong tendency to imitate (far stronger than in other primates), our ability to form prestige hierarchies (with prestige often attached to age, knowledge, and success) rather than just dominance hierarchies, our tendency to preferentially imitate the prestigious, and a tendency to conserve and follow traditions even if we have no understanding of their function.

Henrich also talks about how social structure can affect the pace and degree of cultural evolution. I would parse his argument with the proposition: Cultural evolution varies directly with the size and interconnectedness of social groups. This may be what gave modern humans the decisive advantage over cousin species like the Neanderthals, who had brains at least as large, but apparently much less connected and dynamic social groups.

A corollary of this idea is that small, isolated populations have less cultural bandwidth, and so a reduction in size and connectedness is likely to result in less culture getting transmitted successfully. Phrased as a proposition: Cultural extinction is a direct function of decreasing group size and interconnectedness.

Henrich gives the example of the Tasmanians, who were cut off from the rest of the Australian aborigines by rising seas at the end of the last glacial period. As Henrich puts it: “By isolating the Tasmanians for eight to ten millennia, the rising seas cut them off from the vast social networks of Australia, suddenly shrinking their collective brains.” The result was that their cultural toolkit became progressively simpler, while that of the mainland Aborigines grew more complex.¹

NeoDarwinism and Other Paradigms

I spoke before of the core principles of classical Darwinism being more a logically airtight set of relationships than an empirical proposition about how A influences B. The core logic of natural selection is crucial for explaining evolution, but on its own has few if any implications about evolution’s pace and tempo, or exactly what forms of life it will produce. One has to add additional propositions, like Darwin’s principle of divergence or Hamilton’s rule, to start to make predictions about exactly what will evolve when.

And despite the generally greater level of scientific seriousness in biological science, as compared to social science, I don’t think predictive theory is all that more advanced. The average quality of theory is higher, but that’s driven more by the low end being lower in sociology than the high end being higher in biology. Indeed, when we look at day-to-day explanation in biological subfields, it often bears a curious kinship with sociology. It actually seems to me that other social scientific paradigms sometimes operate within a larger neo-Darwinian framework.

Take functionalism — explaining a part with the needs of the whole. Sociological functionalism took its inspiration from biology, where even in pre-Darwinian times people explained the structure and behavior of organisms with how they kept it alive.

Post-Darwinian biology provides an explanation for why such characteristics exist — natural selection tends to keep those that contribute to inclusive fitness and weed out those that do not. It’s a non-teleological explanation for apparent teleology — and perhaps a non-teleological reason to justify teleology explanation. For much scientific work on organisms is geared toward identifying what function some structure or behavior has in terms of the “goal” of increasing inclusive fitness. Most biologists would insist on the scare-quotes and, if pressed, explain that blind natural selection produces traits that look “as if” they’re pursuing a purpose or goal. But nonetheless some are, like sociological functionalists, content with an explanation that identifies the function of whatever they’re explaining.

Even with neoDarwinism lurking in the background, biological functionalism can have similar shortcomings to sociological functionalism. That something serves this function or that does not necessarily explain variation — such as under what conditions the function will be filled by this means rather than another. And the assumption that existing variation serves a function might be incorrect: Perhaps it is, in the current environment, at least, dysfunctional, or has no consistent impact on inclusive fitness.

On the latter point, Stephen J. Gould and Richard Lewontin famously criticized fellow biologists for assuming everything must be an adaptation, rather than, say, the side-effect of another adaptation or the results of constraints. They also complained that people could glibly posit differing functions for the same trait — is the shape of their faces an adaptation to the weather or to their diet?²

I think they took the criticism a bit far, and that functionalism combined with neoDarwinism generally works better than functionalism without it — largely because neoDarwinism reduces the degrees of freedom to attributing functions to a behavior by forcing us to root it in inclusive fitness, a concept that is in principle readily measurable.

But still we face the problem of actually specifying why these functions or fulfilled in the way they are — that is, of formulating some proposition about what structures and behaviors will evolve when. And we even face the problem of explaining variation in evolution as such — when change will be faster or slower, when extinction will be greater or lesser, and so forth.

And I think neoDarwinian theorists, both knowingly and unknowingly, dip into other explanatory paradigms as they seek ways to specify these conditions. For instance, we might say Hannan and Freeman, when speculating about what increases the structural inertia that prevents adaptation, are drawing on the opportunity paradigm.

The most prominent non-Darwinian paradigm in modern evolutionary theory is the rational choice approach that dominates economics. Its application depends on the logic that natural selection will tend to reward efficient and effective ways of getting one’s genes passed on. This means that, even if no one believes grasshoppers and daisies are literally making rational decisions, they will tend to behave as-if they were pursuing the most efficient way to maximize their inclusive fitness.

Swap “maximize inclusive fitness” for “maximize utility,” and you have the rational actor axiom. With this change, any models developed by rational choice theorists become transferable to the realm of biological evolution.

This logic led to the application of rational choice game theory in evolutionary biology. For example, political scientist Robert Axelrod and evolutionary biologist W.D. Hamilton coauthored on when organisms would evolve to cooperate with one another. Part of their answer was that biologically evolved cooperation emerges under the same conditions that make it a rational choice in the prisoner’s dilemma and other game theoretic scenarios: Repeat interaction, which increases the expected payoff from cooperating and expected cost from defecting.

We see similar applications of game-theoretic thinking to a variety of topics, from how males compete for mates to how well predators will learn to distinguish harmless mimics from their toxic models. Indeed, modern evolutionary theory might be as much rational choice as it is neoDarwinian.

As we look for strategies to specify exactly which conditions will select for this behavior or that, we might draw on other sociological paradigms as well. Along those lines, I recently published a paper claiming the “pure sociology” approach of Donald Black has applications to evolutionary theory.

But now I’m getting ahead of myself! Blackian pure sociology is the last major strategy that I’ll consider in this series, and we’ll address it in the next installment.

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1. Henrich repeats the assertion, which I’ve also read elsewhere, that the Tasmanians lost the ability to make fire. But I recently saw anthropologist Will Buckner refute this on X with an old ethnographic document showing Tasmanian fire-making tools

2. A related issue is that when environments change rapidly, the function something has now might not be the function that first encouraged it to evolve. This is why when explaining human behavior, evolutionary psychologists refer to whatever effect human traits would have had in our ancestral environment rather than in our current one.