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Evolution of Evolution — Text-only | Flash Special Report
Darwin as anthropologist, anthropologists as Darwinians

Cultural evolution hinders application of natural selection to humans

By Ken Weiss

Charles Darwin avoided dealing with human origins in his “On the Origin of Species”(1859). But in “Descent of Man”(1871), he explained human physical traits in the context of primate evolution, correctly identified our African origins and stressed that human variation does not fall into a few racial categories. He offered adaptive explanations for some variable human traits like skin color, but many human traits seemed to confer no physical advantage, and he developed his theory of sexual selection to account for their evolution. In these ways, Darwin was a good anthropologist.

Biological anthropologists are committed Darwinians. We routinely use his principle of descent with modification from a common ancestor in our research, and we integrate genetic, geographic, geologic and fossil data to reconstruct the evolutionary history of primates, including ourselves. We can compare human and other primate DNA sequences to search for aspects of our genome that may reflect natural selection which occurred specifically in our human lineage. Genes that contribute to the adaptive evolution of several relatively simple human traits like skin color or resistance to malaria have been identified.

However, the theory of natural selection presents subtle and difficult problems for anthropology. Darwin wrote that he over-stressed natural selection to show that historical processes alone could account for human origins. In “Expression of the Emotions in Man and Animals”(1872), he used cross-cultural data to identify human behavioral universals in order to show that our species had a single evolutionary origin. He abstained from offering selective explanations in that book, but in “Descent of Man,” he identified important behavioral questions whose evolution is difficult to explain, such as traits like celibacy or self-sacrifice for others, in which individuals seem to voluntarily short-change their own biological interests. The evolution of such traits is still discussed today, and some of Darwin’s ideas accepted. 

Darwin recognized the difference between cultural and biological evolution, but he indulged in rather ethnocentric and unsupported speculation about how natural selection made people in ‘civilized’ cultures superior to people in less technically complex cultures. Proper recognition of Darwin’s legacy must acknowledge that, from his time to the present, it has been easy to be so Darwinian that we incautiously assert what natural selection may have favored in human groups or individuals, making us lesser anthropologists due to the fact that differences may more likely be simply cultural. The value judgments resulting from such speculation have been misused to justify social inequality, racism, eugenics and even genocide.

Ironically, Darwin himself became a lesser Darwinian by saying that modern societies are exempt from the otherwise universal applicability of natural selection, because culture can overcome environments and protect the weak. This overlooks the central fact that culture has alwaysbeen part of the uniquely adaptive context that made us human, and culture has always covered for traits that would otherwise be weak or harmful. 

Darwin transformed our view of ourselves. The great genius of his ideas was their elegant simplicity. But genetic research has shown that both natural selection and the causal connections between genes and the traits that evolution has produced are usually weak, complex and difficult to identify, in part because of our inherently interwoven, ever-changing biocultural evolution. The best way to honor Darwin will be to develop a more integrated anthropology, a challenge that will keep anthropology vibrant for another 150 years.

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Ken Weiss is the Evan Pugh Professor of Biological Anthropology and Genetics at Penn State University in University Park, Penn. He is the author of several books, including “Demographic Models for Anthropology;” “Genetic Variation and Human Disease: Principles and Evolutionary Approaches;” “The Mermaids Tale: Four Billion Years of Cooperation in the Making of Living Things,” with Anne V. Buchanan; and “Genetics and the Logic of Evolution,” also with Buchanan.  His work consists of more than 250 journal articles covering topics such as evolutionary and developmental genetics, complex biological traits and human variation, evolutionary principles, and the philosophy and societal implications of biology. He writes “Crotchets and Quiddities,” a regular column on evolutionary topics, for the journal Evolutionary Anthropology.

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Please see the Resources section for the Bibliography/Additional Reading list for this essay.