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 here, here, 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.
THE NATURAL HISTORY OF HUMAN EVOLUTION
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.
THE CULTURAL AND MORAL HISTORY OF HUMAN EVOLUTION
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.
THE INDIVIDUAL HISTORY OF HUMAN EVOLUTION
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.
REFERENCES
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.
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