Sunday, June 27, 2021

Does the "Dragon Man" Skull Fit the Human Self-Domestication Hypothesis?


Is this a human skull?  Even if it is not human in the sense of belonging to the species Homo sapiens, could it be human in the sense of belonging to the genus Homo?  

The scientists who announced on Friday the discovery of this fossil in China have identified it as the skull of an adult male who belonged to a new human species named Homo longiLong means dragon in Mandarin Chinese, and the fossil was found in the Dragon River region of northeastern China.  Carl Zimmer has written about this in The New York Times (Zimmer 2021), and he has links to the three articles by the scientists announcing the discovery (Ji et al. 2021; Ni et al. 2021; Shao et al. 2021).

The fossil has been dated as being at least 140,000 years old, which means that it is one of the six Homo species that lived on the Earth at the same time as Homo sapiens, which includes Homo erectus, Homo heidelbergensis, Denisovans, Homo luzonensis, and Homo neanderthalensis.  Although they did not all meet one another, we do know that Homo sapiens had intimate contact with Neanderthals and Denisovans--so intimate that we today still have Neanderthal and Denisovan genes.

Studying this "Dragon Man" skull in comparison with all the other fossils of the ancient hominids raises two kinds of questions.  One kind of question is about deciding where this skull belongs in the evolutionary lineage of hominids.  Is it really a new species?  Or does it belong to one of the already identified species?  Some scientists are arguing that it's actually a Denisovan skull.

Another kind of question is about explaining the emergence of Homo sapiens to be the dominant--the only--Homo species on the planet.  Why did those other six hominid species go extinct?  What was so special about our human ancestors that they survived and spread across the globe, while the other hominids disappeared?  This is especially puzzling when one realizes that these other Homo species seem to have been well-adapted for life on Earth.  After all, Homo erectus lived on the planet for a long time--from about 2 million years ago to about 115,000 years ago--longer than our species has.

Explaining how we evolved from ancestral hominids who were similar to us, while also explaining how we evolved to be a unique species, would tell us something about the meaning of our human existence on Earth.

It is often assumed that what makes us unique in the evolution of primates is our large brains as measured by our large craniums, which indicates greater cognitive capacities.  But in fact some of the Neanderthal fossil skulls have a cranial capacity greater than ours.  The Dragon Man skull's cranial capacity is around 1,420 cubic centimeters, which puts it within the range of modern humans.  So the mere size of the human cranium does not by itself explain the human difference.

There are some differences in the fossil skulls that point to ways that Homo sapiens surpasses other Homo species.  One of the most evident differences is in the brow ridges.  Notice how far the brow ridge of Dragon Man projects from the face, much farther out than for a typical Homo sapiens skull.  A similar difference can be seen even within the evolutionary history of Homo sapiens.  The older human skulls show a more prominent brow ridge than the younger human skulls.  Men tend to have thicker, more overhanging brow ridges than women, which is caused by men having higher levels of testosterone than women during their development, particularly during puberty.  So we can say that the skulls of Homo sapiens are more "feminized" than the skulls of other Homo species like Dragon Man, just as younger human skulls are more "feminized" than older human skulls.  You can see this craniofacial feminization in these human skulls:

On the left, you see a 110,000 to 90,000 years-old human male in lateral (top) and frontal (bottom) views, compared to that of a recent African male (right).  The older skull on the left shows the large brow ridges and long and narrow, masculinized face characteristic of Middle Stone Age/Middle Paleolithic-associated humans, as compared to the more feminized face of recent humans.

Some evolutionary biologists--such as Brian Hare (Hare 2017; Hare and Woods 2020) and Richard Wrangham (2019)--have seen this as evidence for the Human Self-Domestication Hypothesis: just as some wild animals have evolved through domestication to become tame animals living around human beings, so have human beings domesticated themselves in that ancient human ancestors were selected for being less aggressive and more socially tolerant individuals; and thus human beings have evolved by self-domestication through what Hare has called "survival of the friendliest."  Some of the evidence for this is found in our anatomy, particularly in our faces.

Dogs were the first animals, and the only large carnivores, to be domesticated.  They were domesticated sometime before 15,000 years ago, and perhaps as long as 30,000 years ago.  They were the only animals domesticated for life with nomadic hunter-gatherers.  They were descended from wolves, particularly from individual wolves with less aggressive temperaments who could live around humans, perhaps feeding on human waste, including human feces.  Dogs have been selected for their friendliness to human beings.  But this selection for friendliness brings with it a suite of developmental, anatomical, and physiological changes, which has been called the "domestication syndrome."  

In his famous experiments with silver foxes, Dmitry Belyaev showed how we can directly observe the evolutionary process by which wild animals become domesticated animals, because he selected wild foxes that showed friendliness to human beings and bred them.  Within 40 years, his breeding for friendliness had created foxes that were as loving to human beings as dogs (Dugatkin and Trut 2017).  As I have written about this in previous posts (here and here), this has suggested to some scientists the possibility that human beings have domesticated themselves in evolutionary history because their ancient ancestors were selected for friendliness just like Belyaev's foxes.

The first test of this Human Self-Domestication Hypothesis came in 2014, when Robert Cieri and his colleagues made some predictions about what would be found in the record of human fossil skulls if this hypothesis were correct.  

They were attempting to solve what paleoanthropologists have called the "problem of behavioral modernity."  The evidence suggests that the first fully human members of Homo sapiens--as indicated by their anatomy--appeared sometime between 200,000 and 150,000 years ago.  But prior to about 80,000 to 50,000 years ago, there is only a little sporadic evidence of "behavioral modernity"--that is, complex symbolic and cultural behavior as indicated by art, ornamentation, hunting and fishing technology, music, and long-distance trade.  The evidence for behavioral modernity manifest in complex symbolic and cultural artifacts becomes prevalent and persistent only after 80,000 years ago.  So why did it take so long for anatomically modern human beings to achieve the behavioral modernity that is unique to human beings?

It has become common for paleoanthropologists to explain this as a result of increasing human populations with dense social networks, so that more people interacting with one another promoted the generation, retention, and diffusion of cultural innovations.  But for this to happen, Cieri and his colleagues argued, there needed to be an increase in social tolerance, so that people in densely populated groups would cooperate with one another rather than fall into conflict.  There had to be some evolutionary selection against aggressive individuals and favoring cooperative individuals.

We should expect to find fossil evidence for this, because the neurotransmitters and hormones that mediate aggressiveness have effects on skeletal development, particularly in craniofacial growth and development.  So if there has been evolutionary selection for social tolerance--for survival of the friendliest--we can expect to see changes in skeletal morphology.

"In addition to moderating social tolerance, androgens play osteogenic roles and are important to the development of sexual dimorphism in craniofacial features . . . . Thus selection against the antisocial behavioral traits associated with high androgen reactivity would be expected to cause a reduction in average androgen levels or receptor density and result in craniofacial feminization in a population over time" (Cieri et al. 2014, 422).

The evolution of craniofacial feminization in Homo sapiens over the last 200,000 years could be seen as a skeletal by-product of an evolution for reduced aggressiveness and increased friendliness similar to what can be seen in domesticated silver foxes, domesticated dogs, and in bonobos.  Lyudmila Trut continued Belyaev's work after his death in 1985.  In 1999, she reported that the domesticated lines of silver foxes showed changes in skull shape.  The domesticated foxes had narrower skulls, with less cranial height, than the farm foxes, so that "the skulls of males became more like those of females" (Trut 1999, 167).  

If human fossils show a similar evolution of craniofacial feminization, this could be evidence for human self-domestication.

To test this prediction, Cieri and his colleagues studied measures of brow ridge projection, facial shape, and endocranial volume in samples of human skulls in three groups.  The samples included 13 skulls ranging in age from 200,000 to 90,000 years ago (Middle Stone Age/Middle Pleistocene), 41 skulls ranging in age from 38,000 to 10,000 years ago (Late Stone Age/Late Pleistocene), and 1,367 skulls of recent humans (Holocene Epoch). 

They found that, on average, skulls from the Late Pleistocene had a 40 percent reduction in how far the brow ridges projected from the face; and they were 10 percent shorter and 5 percent narrower than the skulls from the Middle Pleistocene.  The faces of modern hunter-gatherers were even more feminized than those from the Late Pleistocene.

The fossil evidence of friendliness can be seen not only in skulls but also in fingers.  Emma Nelson and her colleagues (2011) measured the ratio of the second digit (the index finger) to the fourth digit (the ring finger) in ancient skeletons.  For all primates, mothers with high levels of androgen while they are pregnant have babies with ring fingers that are longer than their index fingers.  Men typically have a lower second digit/fourth digit ratio than women.  Chimpanzees have a lower second digit/fourth digit ratio than bonobos.  In both humans and other primates, a lower (more masculinized) second digit/fourth digit ratio is associated with a higher potential for aggression.

Nelson found that the digit ratio of Middle Pleistocene humans was lower (more masculinized) than that of modern humans.  The digit ratio of four Neanderthals was even more masculine.  So it seems that the more feminized digit ratio of modern humans appeared along with their more feminized faces, as indicators of their evolution for friendliness.

I will be writing a long series of posts on this Human Self-Domestication Hypothesis.  And while this might seem to paint a rosy picture of evolved human nature as the friendliest animal, we will see that the picture has a dark side, because our friendliness to others in our group is combined with aggression towards those outside our group.  We are at once the nicest and the nastiest species.

I will also argue that this Human Self-Domestication Hypothesis supports Lockean liberalism, because what Locke identifies as the natural propensity to punish those who violate the law of nature corresponds to the self-domesticating propensity to select against aggressive individuals and to favor cooperative and socially tolerant individuals.  So I will defend a Lockean Liberal Self-Domestication Hypothesis.


Cieri, Robert L., Steven E. Churchill, Robert G. Franciscus, Jingzhi Tan, and Brian Hare. 2014. "Craniofacial Feminization, Social Tolerance, and the Origins of Behavioral Modernity." Current Anthropology 55: 419-43.

Dugatkin, Lee Alan, and Lyudmila Trut. 2017. How to Tame a Fox (and Build a Dog): Visionary Scientists and a Siberian Tale of Jump-Started Evolution. Chicago: University of Chicago Press.

Hare, Brian. 2017. "Survival of the Friendliest: Homo sapiens Evolved via Selection for Prosociality." Annual Review of Psychology 68: 155-86.

Hare, Brian, and Vanessa Woods. 2020. Survival of the Friendliest: Understanding Our Origins and Rediscovering Our Common Humanity. New York: Random House.

Ji, Qiang, et al. 2021. "Late Middle Pleistocene Harbin Cranium Represents a New Homo Species." The Innovation 100132.

Nelson, Emma, Campbell Rolian, Lisa Cashmore, and Susanne Shultz. 2011. "Digit Ratios Predict Polygyny in Early Apes, Ardipithecus, Neanderthals, and Early Modern Humans, But Not in Australopithecus." Proceedings of the Royal Society B 278: 1556-63.

Ni, Xijun, et al. 2021. "Massive Cranium from Harbin in Northeastern China Establishes a New Middle Pleistocene Human Lineage." The Innovation 100130.

Shao, Qingfeng, et al. 2021. "Geochemical Provenancing and Direct Dating of the Harbin Archaic Human Cranium."  The Innovation 100131.

Trut, Lyudmilla. 1992. "Early Canid Domestication: The Farm-Fox Experiment." American Scientist 87: 160-169.

Wrangham, Richard. 2019. The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution. New York: Pantheon Books.

Zimmer, Carl. 2021. "Discovery of 'Dragon Man' Skull in China May Add Species to Human Family." The New York Times, June 25.

Friday, June 18, 2021

The False Rhetoric of Systemic Racism: Charles Murray on Race Differences and America's Ideal of Individual Equality of Rights

 In Facing Reality: Two Truths About Race in America (2021), Charles Murray argues that the rhetoric of "systemic racism" in America is mistaken for four reasons.  

First, it ignores the facts of race differences in cognitive ability and in violent crime.

Second, the rhetoric of systemic racism promotes a group identity politics that denies the American founding ideal that all people are created equal as individuals before the law in their rights to life, liberty, and the pursuit of happiness, and that government should treat all people impartially as individuals and not as members of a group.

Third, this rhetoric of Black identity politics insults all Whites by condemning them as racists who benefit from White privilege, and this is likely to provoke a backlash by some Whites, who could adopt their own White identity politics, which would be disastrous for the whole country and certainly for Blacks.

Fourth, this rhetoric fails to see that while America suffers from the racism of some individuals, this racism is not systemic, because it contradicts the founding ideal of the American system.  Martin Luther King recognized this in his "I have a dream" speech, in which his first dream was that "the nation will rise up and live out the true meaning of its creed: 'We hold these truths to be self-evident, that all men are created equal.'"

Murray offers evidence and arguments supporting these claims, which I find largely persuasive.  But I am not persuaded by his assertion that the "American Creed" affirms a form of government that is contrary to our evolved human nature, which favors tribalism and despotism rather than individualism and liberal democracy.  This implies that the individual rights affirmed in the Declaration of Independence are not natural rights that belonged to human beings in the state of nature, prior to government, as John Locke said.  This wrongly denies the Lockean naturalism of the American founding in the appeal to the "Laws of Nature and of Nature's God," which can now be confirmed by an evolutionary science of human nature.


Black Americans are more likely to be arrested and convicted of violent crimes than are White Americans.  Black Americans are also less likely to have high-paying and high-status jobs than are White Americans.  Proponents of Black identity politics see this as evidence of systemic racism, because they assume that racist discrimination against Blacks is the only possible explanation for why Blacks are on average less successful socially and economically than are Whites.

Murray argues that this ignores two facts about race differences that support an alternative explanation for this situation.  On average, there are race differences in cognitive ability (the mental trait measured by IQ tests) for four racial groups: Whites (or Europeans), Blacks, Latinos, and Asians.  The estimated mean IQ for Whites is 103, for Blacks 91, for Latinos 94, and for Asians 108.  The mean of the bell-shaped distribution curve of IQ scores is skewed slightly to the right for Whites and Asians.  It is inevitable therefore that the most prestigious and highest paying jobs will go mostly to Whites and Asians, because these jobs tend to be the most cognitively challenging jobs.  And while it is common to say that IQ tests are racially biased, the fact that these tests accurately predict performance in the classroom or on the job clearly validates the tests.

The second fact is that across thirteen American cities (including New York, Los Angeles, and Chicago), the Black arrest rate for violent crime (murder, rape, robbery, and physical assault) is around 9 to 11 times the rate for Whites; the Latino arrest rate for violent crime is about 2 to 3 times the White rate; and the Asian arrest rate for violent crime is extremely low.  It is unlikely that this arrest data shows the racism of the police, who might arrest Blacks and Latinos based on scant or fabricated evidence.  This is particularly clear in arrests for murder, where it is usually clear that a crime has occurred.  Moreover, when Blacks are murdered, the perpetrator is usually Black.  In New York City, the dataset of all shootings from 2006 to 2017 show that of the 1,906 Black deaths, 89% were killed by Blacks, 10% were killed by Latinos, and only 0.6% were killed by Whites.  It is hard to explain these higher arrest rates for Blacks as created by a racist criminal justice system.

And yet Murray stresses that these differences in the means (the averages) for racial groups tell us nothing about individuals.  Most of the individuals in all racial groups never commit a violent crime.  And many individuals in every racial group score high on IQ tests.  That's why Murray can say that although racial group differences are important for understanding social problems, these racial differences should not influence how we treat individuals; and even as we recognize these racial differences, we can still affirm the American principle that all individuals are equal in their rights before the law.


Murray sees the American founding principles in the Declaration of Independence as affirming that government should ideally secure the equality of individual rights, with the understanding that this equality means equality of opportunity but not equality of outcome.  People should be equal in their rights under the law.  But they are unequal in their individual traits, so that some will be more successful than others in some sectors of social life.  Even so, all should be equally free to find their places in life where they can pursue the happiness that comes from a lasting, deep, and justified satisfaction with life as a whole.

Murray laments, however, that these founding principles came under attack in 1964 (with the passage of the Civil Rights Act) and in 1965 (with Lyndon Johnson's policy of Affirmative Action).  At this point, some leaders of the civil rights movement began to shift their focus from individual rights in the pursuit of equality of opportunity to group rights in the pursuit of equality of results.  This created a conflict in American ideals between individualism and egalitarianism.

The new egalitarianism assumed that there was no natural human diversity, no differences between the races or the sexes, because all human beings were born with the same abilities and propensities that should produce equal outcomes in life as long as those abilities and propensities were properly cultivated by the social environment.  And therefore any racial or sexual differences in social life must be the product of racist or sexist bigotry favoring White males over women and racial minorities.

To overcome this social injustice from racism and sexism, the American government should promote preferential treatment for Blacks and women--particularly, when they were applying for jobs or for admission to schools.  Originally, affirmative action was a moderate policy of compensatory action to rectify past injustices against Blacks and women: if there were Black and female applicants for a job or a school who were as well qualified as the White male applicants, those Black and female applicants should be favored.  But then affirmative action became an aggressive policy of preferential treatment in which even less qualified Blacks and women would have to be chosen.  And so, for example, as Murray shows, the elite universities in America have accepted Black applicants whose admission test scores are far below those for White applicants who have been denied admission.

Murray identifies this aggressive affirmative action as "a poison leaking into the American experiment" (121).  Government is no longer an impartial judge that treats all individuals as equal under the law.  Now government gives preferential treatment to some minority racial groups over the White majority.  All Whites are said to be racists who succeed in life only because of White privilege, and therefore they need to admit their guilt for systemic racism, while the government punishes them and rewards Blacks.  Indeed, Murray observes, one might as well call affirmative action systemic racism, because it systematically discriminates in favor of racial minorities other than Asians (88).

As Whites now see the success of Black identity politics, Murray worries, what's to stop some of the Whites from playing White identity politics?  And then it will be a battle between the White 60 percent of the population against the Black 13 percent.  The catastrophe of a civil war like the American Civil War becomes a fearful possibility.

How do we escape this?  Murray suggests two possible solutions.  The "solution that is not within our grasp," because it is not politically possible, would be to eliminate all governmental preferential treatment by race (120-22).

The "partial solution that is within our grasp" would be for American political leaders to publicly embrace as the American creed the original American ideal of individual equality under the law (122-25).  Murray recognizes that even if the leaders of the Democratic Party were to do this, beginning with President Biden, they would still want to pursue some policies of racial preferences.  But they could at least say that these were only temporary policies, and that individual equality before the law was the ultimate goal.  They would also have to reject the rhetoric of systemic racism.  It seems unlikely that Biden would do this since he has already declared his commitment to policies to attack systemic racism.


Despite my agreement with most of what Murray has said here, I disagree with his argument that group identity politics could easily destroy the American founding regime since that regime has always been fragile, and it's fragile because it is "extremely unnatural" in the sense that it is "in conflict with human nature."  

Murray's thinking that the American regime has no grounding in human nature seems to explain why he so often uses the term "American Creed." The word "creed" originally referred to the articles of belief for the Christian Church, as in the Apostles', Nicene, and Athanasian Creeds.  "Creed" is derived from the Latin credo, as in the beginning of the Apostle's Creed: Credo in Deum--I believe in God.

Similarly, Murray declares that "bearing witness to our true faith and allegiance in the American creed is something within our power to do" (125), as if American principles depended on some willful faith or belief in a transcendent reality beyond any natural human understanding.  Of course, the Declaration of Independence does speak of our being created equal and endowed by our Creator with rights, which suggests some religious belief.  But when the Declaration appeals to "the Laws of Nature and of Nature's God" (a phrase that Murray never mentions), this implies a Spinozistic conception of God as identical with Nature.  Certainly, Jefferson and the founders were clear that the rights affirmed in the Declaration were natural rights, the rights that human beings had in the state of nature as governed by the law of nature.  Here they followed John Locke, who often invoked the "principles of human nature" that should govern any just government.

Murray seems to think that Locke was wrong about this, because our human nature as shaped by evolution does not incline us to recognize or respect the equal rights of individuals.  Here is the long passage where Murray explains this:

"Treating our fellow human beings as individuals instead of treating them as members of groups is unnatural.  Our brains evolved to think of people as members of groups; to trust and care for people who are like us.  Those traits had great survival value for human beings throughout millions of years of evolution.  People who were trusting of outsiders were less likely to pass on their genes than people who were suspicious of them.  People who were loyal to their tribe were more likely to pass on their genes than people who stood apart."

"The invention of agriculture and the consequent rise of complex societies exposed another aspect of human nature that had enjoyed less scope for expression in hunter-gatherer bands: acquisitiveness, whether of money, status, or power. . . ."

"The combination of acquisitiveness and loyalty to the interests of one's own group (be it defined by ethnicity or class) shaped human governments for the subsequent ten thousand years.  The natural form of government was hierarchical, run by a dominant group that arranged affairs to its benefit and oppressed outsiders. . . ."

 "America proved that a durable alternative to the natural form of government was possible--a constitutional republic combined with carefully circumscribed democracy. . . . If we decide that our system for tending the garden needs to be replaced, and if the replacement should prove to be even slightly less devoted to keeping nature at bay, the garden will be reclaimed by jungle within a few decades" (110-11).

Oddly, what Murray says here contradicts what he has said in some of his other books.  For example, in In Pursuit: Of Happiness and Good Government, Murray said that the Founders understood equality to be rooted in "the nature of man."  He quoted favorably Martin Diamond's comment that "the modern idea of human nature is democratic: no difference among us can reach so far as to alter our naturally equal humanness."  Murray also wrote that "equality meant that all men shared as their birthright the same natural rights of liberty.  All were equally immune by right from the arbitrary coercion of the state" (140-42). 

As I have said in some previous posts (herehere, and here), I agree that tribalism is part of our evolved human nature.  But that is only one side of our nature.  We also have evolved natural propensities to resist exploitation and to punish those who would dominate us and deny our individual natural rights to equality and liberty.  Locke's account of the state of nature as a state of natural equality and liberty can be confirmed by the Darwinian account of our evolution in ancient hunter-gatherer bands.

Contrary to Murray's identification of despotism as "the natural form of government," I suggest that Spinoza was correct when he said that liberal democracy was "the most natural state," because it approaches the freedom that humans enjoyed in the state of nature.

There is lots of scientific evidence that human beings evolved a dual nature as both the nastiest and the nicest species, which can be explained by an evolutionary process of human self-domestication in which natural selection favored the friendliest individuals who could cooperate with others in ways that set us apart from other species.  I have written about this in some posts hereherehere, and here.

I will have more to say about "the human self-domestication hypothesis" in some future posts.

I have written many previous posts on how what Murray says about human biodiversity supports the natural right to equal liberty.  A few of them can be found hereherehere, and here.

Tuesday, June 08, 2021

Biopolitical Science in Darwin's DESCENT OF MAN: The Coevolutionary History of Nature, Culture, and Individuals

Charles Darwin's Descent of Man was published on February 24, 1871.  So this year is the 150th anniversary of its publication.  This has prompted some recent articles--including a particularly good one by Richerson, Gavrilets, and de Waal (2021) in Science--and a book edited by Jeremy DeSilva (2021) assessing Darwin's account of human evolution Descent in the light of modern evolutionary science.

On some points, we can see that Darwin was mistaken.  For example, he claimed that because of their distinct roles in the sexual division of labor, women were intellectually inferior but morally superior to men.  In 1875, only four years after the publication of Descent, Antoinette Brown Blackwell showed that Darwin's evidence did not support his conclusion about the intellectual inferiority of women, and that the correct inference from the biological facts was that the sexes are "true equivalents--equals but not identicals."  I have written about this in Darwinian Natural Right (123-160).

His most fundamental mistake was in trying to explain the inherited transmission of parental traits to their offspring through the "hypothesis of pangenesis"--the idea that every part of the body emits tiny particles ("gemmules") that migrate to the gonads and then are transmitted to offspring, so that the gemmules develop into their associated body parts as the offspring matures (Darwin 2004, 264-267).  Unfortunately, Darwin knew nothing about Gregor Mendel's experiments that provided the first evidence for genetic inheritance.  Mendel knew a lot about Darwin, however, and he agreed with Darwin's theory of evolution.  In his handwritten annotations in his copies of Darwin's books, Mendel endorsed most of Darwin's reasoning, while correcting what he said about pangenesis (Fairbanks 2020).  In his annotations of The Variation of Animals and Plants Under Domestication, Mendel highlighted those passages where Darwin admitted that pangenesis was "merely a provisional hypothesis or speculation," and that "the existence of free gemmules is a gratuitous assumption."  Mendel was an Augustinian friar, and he was condemned by those in the Catholic Church who regarded his support for evolution as a denial of the Catholic doctrine of Creation.

For me, rereading The Descent of Man today is instructive in two ways.  First, while some evolutionary biologists have criticized the "modern evolutionary synthesis" as being too "gene-centric" in not recognizing the importance of cultural evolution, most of what they have proposed as part of an "extended evolutionary synthesis" can be found in The Descent of Man.  In particular, Darwin stresses the importance of cultural evolution, including moral evolution, for explaining human biological nature.  This is what Richerson, Gavrilets, and de Waal mean in saying that Darwin's Descent "foreshadowed" modern theories of human gene-culture coevolution.  I have written about this in previous posts here and here.

Darwin's Descent is also instructive for me because it largely supports what I have called "biopolitical science," which requires a three-levelled analysis of political history as showing the unity of political universals, the diversity of political cultures, and the individuality of political judgments.  I have worked through these three levels of biopolitical history as they are generally manifested in human politics and as they were particularly illustrated in Abraham Lincoln's decision to issue the Emancipation Proclamation in 1863 (Arnhart 2012).  This idea of biopolitical science first came to me in 1986 when I read Jane Goodall's Chimpanzees of Gombe, and I saw that this was a political history of the chimps at Gombe showing the natural history of chimpanzee politics, the cultural history of this particular chimpanzee community, and the biographical history of the unique individuals in that community.  I have written some posts on this herehere, and here.

I have argued that a Darwinian social psychology needs to understand the interaction of genetic history (the evolutionary psychology of Tooby and Cosmides), cultural history (the cultural group selection of Richerson, Boyd, and Henrich), and biographical history (the evolved personality and life history of self-interested individuals who are agents of cultural change acting through coercion or persuasion, as presented by Singh, Wrangham, and Glowacki).

There is a complex coevolutionary interaction between these three levels of history.  Genetic history enables and constrains, but does not determine, cultural history.  Genetic history and cultural history jointly enable and constrain, but do not determine, biographical history.

The interaction also moves in the opposite direction: biographical history enables and constrains, but does not determine, cultural history; and biographical history and cultural history jointly enable and constrain, but do not determine, genetic history.

A famous illustration of how cultural history can shape genetic history is the evolution of adult lactose tolerance (Durham 1991; Gerbault et al. 2011).  Most human beings around the world today cannot easily digest milk, because after weaning from their mother's milk, they no longer produce lactase, an enzyme necessary for digesting the sugar lactose in milk.  This was probably true for most human beings throughout evolutionary history.  But then in pastoral societies with cultural traditions of dairying, milk was available as food for adults, which created a cultural environment in which genetic mutations for the production of lactase in adults would be favored by natural selection.  The people today who are lactose tolerant are descendants of those human beings who lived in dairying cultures.  Their genetic history was shaped by a cultural history favoring the evolution of lactase persistence as human niche construction.


Despite Darwin's ignorance of genetics and the very skimpy fossil evidence of human evolution available to him, he was able to infer the general pattern of human evolution from primate ancestors.  He saw that of the living primate species, the gorilla and chimpanzee were most closely related to human beings; and since these apes lived in Africa, he speculated that the earliest human ancestors must have originally evolved in Africa, and then their ancestors migrated out of Africa to spread out over the Earth (Darwin 2004, 182).  As Richerson, Gavrilets, and de Waal (2021) have shown, the research since Darwin has filled in the details of this general pattern of phylogenetic descent of Homo sapiens from primate ancestors in Africa.

Moreover, they indicate that research in neurobiology, genetics, primatology, and behavioral biology has confirmed Darwin's insight that although there appear to be great gaps in the mental faculties of human beings and other animals, human cognitive capacities "do not differ in kind, although immensely in degree" from the cognitive capacities of other animals (Darwin 2004, 173).  They do not notice, however, that Darwin contradicts himself on this point when he says that humans really are different in kind in their unique capacities for language, morality, and symbolic abstraction.  As I have claimed in some previous posts, Darwin could have escaped this contradiction if he had seen the distinction between emergent differences in kind that can be explained by natural evolution and radical differences in kind that suggest some supernatural special creation.  Richerson, Gavrilets, and de Waal implicitly recognize the uniqueness of human language as an emergent difference in kind when they admit that communication among other animals does not manifest "the syntax, recursiveness, and rich meaning of our learned symbolic communication" (2).  Symbolic language is crucial for human cultural and moral evolution because it is the most effective means for formulating and transmitting social norms.


A crucial part of Darwin's theory of human evolution in The Descent of Man was his account of human cultural and moral evolution.  "Ultimately our moral sense or conscience becomes a highly complex sentiment--originating in the social instincts, largely guided by the approbation of our fellow-men, ruled by reason, self-interest, and in later times by deep religious feelings, and confirmed by instruction and habit" (2004, 157).  In developing this thought, he was influenced by the Scottish tradition of moral philosophy through his reading of David Hume, Adam Smith, and James Macintosh.  He thus rejected the Kantian tradition of moral philosophy in which culture and morality were seen as a uniquely human realm of activity that transcended human nature.

Remarkably, even some of Darwin's strongest supporters--including Alfred Russel Wallace and Thomas Huxley--rejected Darwin's naturalistic account of moral culture because they believed that one could never derive moral values from natural facts.  They assumed that human morality belonged to a transcendent realm of cultural artifice and free will that is beyond the natural realm of causal forces open to scientific study.

Until recently, even most of the  leading thinkers in evolutionary psychology--such as John Tooby, Leda Cosmides, and David Buss--rejected Darwin's evolutionary theory of morality.  Over the past 20 years, however, many of these people have moved towards thinking that Darwin was right about this.  Closely related to this is the growing recognition that culture is not uniquely human, because other animals have cultural traditions.  Richerson, Gavrilets, and de Waal rightly see these intellectual movements as confirming Darwin's original insight that explaining culture and morality belongs to the evolutionary science of biology.

Richerson, Gavrilets, and de Waal fail, however, to clearly indicate that human culture and morality really are humanly unique insofar as they depend on the human capacity for symbolic abstraction.  Although other animals have behavioral inheritance systems based on the transmission of information among animals through social learning, only human beings have symbolic inheritance systems in which they think about abstractions that have little to do with concrete, immediate experiences.  Symbolic systems allow human beings to construct a shared imagined reality.  Art, religion, science, philosophy, and morality are all manifestations of human symbolic evolution.  Richerson, Gavrilets, and de Waal suggest this when they refer to "the symbolized nature of human culture" (3).

A biopolitical science must explain this symbolic evolution as the realm for political rhetoric and political philosophy.  For example, we might explain Lockean liberalism as the symbolic niche construction of liberal institutions.  Similarly, we might describe this, as it is by Deirdre McCloskey, as a rhetorical transformation in ethical ideas, moving from an aristocratic ethics that scorned the pursuit of trade and economic gain to a bourgeois ethics in which life in a commercial society became virtuous.


Animals are individuals with characteristic personalities that distinguish one individual from another, and this individuality influences their evolutionary history.  In The Descent of Man, Darwin suggested this when he observed that animals often display their "mental individuality" (106).  He saw evidence for the importance of human individuality in shaping human cultural evolution in Francis Galton's Hereditary Genius (first published in 1869).  Darwin and Galton recognized that the fertilization of an egg created an individual life with an innate predisposition for developing an individual personality (Galton 1972, 426-28).  Some individuals were endowed with the potential for genius, and in the right social circumstances they could invent new ideas and practices that would advance cultural progress.  Darwin observed: "Great lawgivers, the founders of beneficent religions, great philosophers and discoverers in science, aid the progress of mankind" (2004, 162).

Darwin indicated how this progress arises from the complex coevolutionary interaction of individual history, cultural history, and natural history:
"The more efficient causes of progress seem to consist of a good education during youth whilst the brain is impressible, and of a high standard of excellence, inculcated by the ablest and best men, embodied in the laws, customs, and traditions of the nation, and enforced by public opinion.  It should, however, be borne in mind, that the enforcement of public opinion depends on our appreciation of the approbation and disapprobation of others; and this appreciation is founded on our sympathy, which it can hardly be doubted was originally developed through natural selection as one of the most important elements of the social instincts" (2004, 169).

At the level of natural history, natural selection has shaped the innate social instincts of human beings, which make them sensitive to the approbation or disapprobation of people in their community.  At the level of cultural history,  this concern for social conformity motivates human beings to learn the social norms of their group.  At the level of individual history, those talented individuals with persuasive influence or authority over the group can select the social norms that will be enforced by public opinion.

After Darwin, for a long time, many biologists were not interested in studying the evolution of individual animal personalities, because they assumed that evolution would shape a species typical psychology shared by all individuals of the species with little heritable variation.  Evolutionary psychologists (like Leda Cosmides and John Tooby) have concentrated on human universals as evolutionary adaptations shared by all human individuals.

But  in recent decades, the biological study of animal personalities has become one of the hottest topics in biology.  One of the most extensively studied models of human personality among psychologists is the Five Factor Model that describes human personality differences across five domains--Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism (OCEAN).  Each domain corresponds to an axis running from high to low.  So, for example, those individuals high in Agreeableness tend to be helpful, trusting, and cooperative with everyone.  Individuals lower in Agreeableness tend to be less helpful, more suspicious of others, and more competitive than cooperative.

This same Five Factor Model can be applied to the study of nonhuman animal personalities, using the same methods as are used in studying human beings.  Four of the factors appear in many animal species.  But Conscientiousness seems to appear only among chimpanzees and human beings.  One possible explanation for this is that Conscientiousness requires a high cognitive ability for making plans and controlling impulses in executing those plans, which requires the large frontal lobes found only in chimps and humans.

The five factors of personality have been found to be highly heritable and thus genetically influenced.  But these factors also vary according to environmental experience, particularly the environment of early experience, which influences personality throughout life. So personality seems to arise from genetic predisposition, from environmental learning, and from the interaction of genes and environment (including the cultural environment).  Through experimentation with animals in the wild and in laboratories, scientists can make testable predictions about the genetic and environmental causes of personality. 

It is possible that the cultural evolution of the bourgeois virtues in modern liberal societies depended on an evolutionary history favoring personality traits like high Agreeableness and high Conscientiousness.  The evidence from cross-cultural economic game experiments that show that being integrated into market exchange is correlated with a greater sense of fairness might support this conclusion.

Just as we have bred domesticated animals to favor those personality traits that we find desirable, we might understand human culture as self-domestication that selects for those personality traits that are adapted to the culture.  The "human self-domestication hypothesis" has been defended by Hare and Woods (2020) and Wrangham (2019).  We might be like those silver foxes who were bred by Dmitri Belyaev for docility, which I wrote about in a previous post.


Arnhart, Larry. 2012. "Biopolitical Science."  In James E. Fleming and Sanford Levinson, eds., Evolution and Morality, 221-265. New York: New York University Press.

Darwin, Charles. 2004 [1879].  The Descent of Man, and Selection in Relation to Sex. 2nd edition. 
New York: Penguin Books.

DeSilva, Jeremy, ed. 2021.  A Most Interesting Problem: What Darwin's "Descent of Man" Got Right and Wrong About Human Evolution.  Princeton, NJ: Princeton University Press.

Durham, William H. 1991. Coevolution: Genes, Culture, and Human Diversity. Stanford, CA: Stanford University Press.

Fairbanks, Daniel J. 2020. "Mendel and Darwin: Untangling a Persistent Enigma." Heredity 124: 263-273.

Galton, Francis. 1972 [1892].  Hereditary Genius: An Inquiry into Its Laws and Consequences. 2nd edition. Gloucester, MA: Peter Smith.

Gerbault, Pascale, et al. 2011. "Evolution of Lactase Persistence: An Example of Human Niche Construction." Philosophical Transactions of the Royal Society B 366: 863-877.

Hare, Brian, and Vanessa Woods. 2020. Survival of the Friendliest: Understanding Our Common Humanity. New York: Random House.

Richerson, Peter J., Sergey Gavrilets, and Frans B. M. de Waal. 2021. "Modern Theories of Human Evolution Foreshadowed by Darwin's Descent of Man." Science 372: eaba3776.

Singh, Manvir, Richard Wrangham, and Luke Glowacki. 2017. "Self-Interest and the Design of Rules." Human Nature 28: 457-480.

Wrangham, Richard. 2019. The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution. New York: Pantheon Books.