Cultural Evolution

/ by Paul Ehrlich /

Does human culture evolve via natural selection, as our genes do?

Illustration by Studio Commonwealth

Biologists have a pretty good idea of both how flies become resistant to DDT and how humans and primates have diverged over time. That’s because the mechanism underlying these processes is the same. Using evolution we can understand how organisms generally change their stores of genetic information (DNA and RNA), alter their observable characteristics, and diversify.

We do not understand how cultures evolve nearly so well. The majority of human evolution does not involve changes in our DNA, but rather alterations in the gigantic library of nongenetic information, the culture, that our species possesses. This library is orders of magnitude larger than that of our genetic information, and the elements on its diverse shelves usually have meaning only in connection with other elements. Indeed, there has been a long, bitter debate about whether it is sensible even to use the term evolution to describe changes in culture. After all, culture is composed of overlapping phenomena from languages, religions, institutions, and socially transmitted power relationships to the information embodied in artifacts ranging from potsherds to jumbo jets. The study of cultural change encompasses not only the disciplines of biology and the social sciences, but areas of the humanities as well.

Despite the great difficulties of building a comprehensive theory of cultural change deserving of the label of “evolution,” progress in that direction has begun. We are finally starting to understand the patterns of culture change and the role of natural selection in shaping them. And since everything from weapons of mass destruction to global heating are the results of changes in human culture over time, acquiring a fundamental understanding of cultural evolution just might be the key to saving civilization from itself.

ATTEMPTS TO DETECT BROAD PATTERNS in cultural change extend about as far back as we have historical records. In the modern era, Baron de la Brède et de Montesquieu (1689-1755) described soil fertility, climate, and natural barriers as factors that shape cultures. In fact, he foreshadowed the analyses of Jared Diamond’s classic book, Guns, Germs, and Steel. Montesquieu was also very much concerned with how cultural change might be channeled, examining governance issues such as the separation of powers, which also drew the attention of thinkers like Aristotle and Locke. How to maintain cultures that preserve that separation has worried American politicians from the 1770s to this day.

A lot of controversy has centered on whether changes in culture are best viewed simply as “history” or whether there are patterns. This controversy has gained steam in part because some view cultural evolution as “progressive”: the unfolding of a predetermined law leading from “primitive” hunting-and-gathering societies to “advanced” industrialized cultures. Biologists long ago gave up the idea that genetic evolution was progressive. A careful look at culture shows that any attempt to determine what is “advanced” is hopeless. Instead, Joseph Tainter and Robert Edgerton have established standards by which some societies may be considered “sick”—they follow cultural practices leading to their own destruction.

If we wish to understand and predict culture change generally, viewing culture as an evolving trait in analogy with genetic evolution is a very useful place to start. If geneticists can predict the evolution of antibiotic resistance in bacteria and discover ways to slow it, couldn’t cultural evolutionists develop recommendations for keeping disputes from evolving into wars? Couldn’t they steer us toward seriously attacking climate change? Many researchers interested in cultural change have tried models based on Darwinian evolution. Unfortunately, there’s a major problem with this approach: It ignores how ideas actually arise and spread in cultures.

There were many competing notions of biological evolution floating around in Darwin’s day. Perhaps the best known was that of Jean-Baptiste Lamarck, in which organisms changed according to their use or disuse of attributes and passed the results on to their offspring (e.g., giraffes that stretch their necks to reach leaves high on trees pass on their longer necks). Lamarck was largely wrong about the mechanism of evolution and wrong in his view (still too common) that evolution was directional, from simplicity to complexity. Darwin’s triumph came in recognizing that organisms within populations varied, that traits could be passed on to offspring, and that offspring with some traits would out-reproduce those with others. He and Alfred Russell Wallace recognized that such “natural selection” was the principal creative force in what we now think of as genetic evolution.

But this does not resemble what we know of cultural evolution. Parents, for example, pass on to their children skills acquired by a lifetime of experience, not merely what they acquired from their own parents. Models of cultural change clearly need a large Lamarckian component.

My Stanford colleagues Luca Cavalli-Sforza and Marcus Feldman have done pioneering work on cultural evolution, including its Lamarckian features. They were the first to systematically examine patterns of cultural transmission and the resultant spread of behaviors. For example, Cavalli-Sforza and Feldman modeled different modes of transmission of a small-family-size norm among Italian women between 1800 and 1950, including the disadvantage in natural selection that would occur. They demonstrated formally that the new idea of small families could be attractive enough to overwhelm the force of natural selection against it. Indeed, the importance of cultural change is underscored by its power to counter natural selection, as dramatically evidenced by the trend toward smaller family sizes in the majority of nations today.

There are clear patterns in cultural evolution, which are just as prevalent as those in genetic evolution. Many other examples have been found, including the rise of states where people are not free to escape despotic chieftans; the repeated successes of Rommel in North Africa in World War II; and the failure, for lack of suitable draft animals, of the Aztecs as opposed to the Assyrians to employ wheels for use in transport and warfare.

Cultural evolutionists such as George Basalla, Robert Boyd, Barry Hewlett, Peter Richerson, and Everett Rogers have made considerable progress in examining the patterns behind how and why cultures evolve. But the field has not yet produced a Darwin—someone who has persuasively demonstrated the major “creative” force in cultural evolution. And certainly, no Mendel has appeared to postulate exactly what is changing as culture evolves. Richard Dawkins’s brave conjecture about “memes” (gene analogs) being discrete units of cultural inheritance has not proved entirely fruitful—and the analogy is in retrospect far-fetched. Genes are passed unidirectionally between parent and offspring, and the recipients must accept them. Memes could be passed hundreds of generations at a leap (Aristotle to you), horizontally among peers (gang member to gang member), backwards in generations (learning from your grandkids), and so on. And, unlike genes, not only can cultural inheritances be rejected but they can also be purposefully modified.

We should not find our lack of success too discouraging. Molecular genetics is also rapidly removing some of the simplicity once associated with what genes are and how they function without much change in the larger macroevolutionary theory. What we need is a simple place to start.

RECENTLY, SIMON LEVIN and I suggested a hypothesis that could put regularities in cultural evolution to an empirical test. We believed that the evolution of technological norms would generally be more rapid than that of ethical norms. After all, technological changes are often tested promptly against environmental conditions. Round wheels are selectively favored over—or out-reproduce—hexagonal ones every time. Ethical systems, on the other hand, cannot be easily or unambiguously compared with one another. Standards of success often vary from observer to observer and are the subject of ongoing controversy. How rapidly, for example, did individual freedom replace slavery and indentured servitude in various societies? How does the inferior position of women in virtually all societies enter into this calculus? Is freedom in any significant sense tested against the environment?

Trying to find a model system in which to test the hypothesis that cultural evolution would go on at different rates depending on environmental testing, I decided to look at cultural features in Polynesia. This is the geographic location most recently settled by Homo sapiens (~2500 years) and one where the sequence of colonization has been pretty well uncovered through archeological, linguistic, and genetic evidence. Also, there are preexisting ethnographies for most Pacific island cultures.

At first I tried to compare agricultural crops and techniques (which are clearly tested against the environment) with the number of gods (not likely to be environmentally tested) across cultures. Unfortunately, ethnographies are written more like novels than scientific studies, and it is impossible to be certain of all the crops grown and the counts of deities. Then I discovered a very large, data-rich work by the anthropologists Alfred Cort Haddon and James Hornell on the canoes of Oceania, from which I could tabulate the canoes’ properties. There were functional traits, such as whether the canoes were dugouts (made from a single log) or built from boards lashed together. There were also symbolic traits, such as whether they were decorated with inlaid shells or had carved figureheads. According to my hypothesis, the former characteristics would be much more severely tested against the environment than the latter.

It is difficult to properly categorize traits and do the complex statistical analyses required to test the hypothesis of culture change. Fortunately, my collaborator Deborah Rogers was able to sort out the complexities of trait evaluation in the canoes (96 functional features, 38 symbolic). After her analyses it was immediately clear that the functional traits—those we thought would affect survival, migration, and reproduction—evolved more slowly than the symbolic ones. The original Ehrlich-Levin hypothesis was rejected. In retrospect the reasons seem clear. If the boards lashed together to make your canoe were to come apart during a long voyage, that would have a greater impact on your survival than if your paddle wasn’t painted with an attractive design.

Natural selection in this case appears to have favored gradual changes in structural design rather than rapid adoption of novelties. Presumably, selection slowed down the change in structural features because time-tested designs enhanced success and survival in migrations, fishing, and warfare more than the accidental variants in canoe construction. A parallel example would be that once a society progressed from hexagonal to round wheels, selection would stabilize the wheel shape at round—tending to operate against, say, elliptical wheels. In contrast, ornamentation diversified rapidly, possibly because people like to distinguish themselves from others (think of national symbols or clothing styles). There is little or no evolutionary cost for this—changing a painted design is unlikely to cause a canoe to become unseaworthy.

The importance of our result was not what it told us about canoes. We directly tested a theory of cultural evolution. Our work has helped to uncover a piece of the larger, more complex process of culture change and has shown that it is reasonable to think of that change as evolution. Natural selection can operate in cultural evolution as well as in genetic evolution. Though canoe features may not be related to the genetic attributes of people who construct and use them, nor is natural selection likely the central force in cultural evolution, a comprehensive view of cultural evolution does now seem possible. And despite the daunting complexity, I believe we will one day understand how cultures evolve, and that it will help us all to survive.

Originally published June 23, 2008

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