A complex, diverse, and ever changing culture is one of the most distinctly human characteristics. Sure, depending on how exactly one defines “culture” some other animals, especially some of our closest primate kins, have culture. But you know what I’m talking about: music, art, literature, the Kardashians, blogging, that sort of thing.

Because culture is so fundamental to who we are, it is no surprise that scholars have been studying culture(s) and trying to come up with general theories explaining them for a long time. This used to be pretty much the exclusive domain of the humanities (literature, cultural anthropology). But then it expanded to the social sciences (psychology, sociology), and now the fray has been entered by the natural sciences, in particular biology.

For instance, one of the early attempts at importing the tools of the natural sciences into the study of cultural change (or cultural “evolution”) was done by biologists who used the mathematical arsenal of population genetic theory to study what they termed gene-culture co-evolution.

Another, more popular, approach stemmed out of Richard Dawkins’ famous coinage of the term “meme” in his popular book, The Selfish Gene. Dawkins was looking for some example — outside of biological evolution — that could buttress his idea that the Darwinian principle of evolution by natural selection is more broadly applicable than its historic focus on genes and their effects on organismal fitness. A “meme,” then, is supposed to be a unit of cultural evolution, which gets “replicated” and “selected” in a natural environment provided by human minds.

The problem with these approaches is that they are either limited in scope or turn out not to work particularly well. There are indeed some well documented and well understood examples of gene-culture co-evolution, for instance the transition to dairy foods, which evolved independently a number of times, for instance in Europe and the Middle East around 6-10,000 years ago. It triggered the selection of gene variants responsible for the production of the lactase enzyme, which is necessary for the digestion of consumed milk. Human behavior and human genetics in this case go hand in hand, one influencing the other in a continuous causal loop. The limitation of this approach to the study of culture, however, is that it works well only for traits with relatively simple genetic bases, and it really doesn’t extend at all to a lot of things that fall under the rubric of “culture” more broadly construed.

That’s why memetics (i.e., the study of memes) was initially regarded by some as more promising. The concept of meme is inherently flexible, and can be applied to anything from a catchy tune to “religion” (a complicated and highly variable concept, often referred to as a memeplex). But pretty soon a number of problems emerged with the very idea of memes. For one, the concept is too flexible, so much so that one doesn’t really know what, exactly, counts as a meme (or if anything doesn’t count). Also, not only we have no idea about the physical substrate of memes (unlike genes, which are made of nucleic acids), it isn’t even clear whether memes are necessarily linked to particular substrates at all (neural pathways? The hard disk on your computer?). More crucially, when people say that meme X has been selected in favor while meme Y has been selected against, they are simply restating an observation (X is popular, while Y is not), without providing any detail about the selective mechanism. If biologists did that with the theory of evolution they would rightly be accused of circularity (as in “selection leads to the survival of the fittest; the fittest are those who survive”). In other words, memetics doesn’t have a functional, ecological theory of why certain memes are selected in favor or against. Without it, the approach has next to zero explanatory power. Sure enough, after a brief spurt of activity, the Journal of Memetics closed down, and the whole approach survives as a popular culture metaphor, but not as an active scholarly research program.

Then what? Are there other ways to study cultural evolution from the point of view of the natural sciences? Sort of. A recent paper by Alberto Acerbi and Alex Mesoudi, published in Biology and Philosophy, tries to clear the air from a lot of confusion in the field of Darwinian cultural evolution (the pdf is available for free).

Acerbi and Mesoudi make clear what the problem is: “Cultural evolution studies are characterized by the notion that culture evolves according to broadly Darwinian principles. Yet how far the analogy between cultural and genetic evolution should be pushed is open to debate.” The bulk of their paper is an attempt to contribute to that debate by clearing up a lot of confusion that has arisen in the field when people talk about specific mechanisms of cultural evolution, and in particular the difference between cultural selection and cultural “attraction.”

Cultural selection is “a process of selection between different variants (e.g. beliefs, ideas or artefacts) or models (referring to people from whom one can copy).” The alternative is a situation in which “the permanence of some cultural traits occurs not due to high fidelity cultural transmission but instead due to the existence of stable ‘cultural attractors.’”

An example of cultural selection is how people chose the name of a newborn baby from a pool of available candidate names. An example of cultural attraction is when people transmit a story, like that of Cinderella. In the first case, the replication is accomplished by high-fidelity copying; in the second case, however, the cultural trait is “reconstructed,” and the process has relatively low fidelity.

Acerbi and Mesoudi are interested in unpacking these two notions, sharpening them up, pointing out where exactly they differ, and then argue that both processes occur during, and account for, cultural evolution. Which mechanism is prevalent under what circumstances then becomes an empirical question (though not necessarily an easy one).

A nice potential example of empirical study of cultural attraction is a paper published by O. Morin in 2013 in Evolution and Human Behavior (behind paywall). It concerns the difference between direct and avert eye gaze in aesthetic portraits. Morin was able to show that portraits featuring direct eye gaze are more frequently reproduced in books, as well as that such portraits have increased in popularity over time. The interesting bit is that individual painters did not change their style, so the eventual prevalence of direct eye gaze portraits is the result of cultural preference. Morin proposes that the apprentices of various painters modified their own style in the direction of the “direct gaze” attractor and away from its alternative, or that the apprentices selectively copied direct gaze paintings because they were more popular.

This example shows that it is possible to conduct solid research in cultural evolution studies, but it also makes it clear just how difficult it is to get to the mechanisms of cultural evolution: the two proposals made by Morin fall into the two camps discussed by Acerbi and Mesoudi, the first being an instance of cultural attraction, the second of cultural selection. Which one was it? Or, more likely, what combinations of the two took place? It’s (very) hard to tell.

And much of the above is predicated on a crucial assumption, which is not shared by everyone: that cultural evolution really does take place according to something akin to a Darwinian mechanism. But what, precisely, is a Darwinian mechanism?

“Darwinian” is a specific modifier of “evolution,” so we cannot simply equate Darwinism with evolution. Evolution, in the broadest sense possible, simply means change over time. As in the universe has changed since the Big Bang. But that is not a theory of mechanisms, it’s a neutral description. Life also evolved in that general sense of the term, but if that were all that Darwin said we wouldn’t have a science of evolutionary biology.

The most famous, and still in my mind most clear, formal definition of Darwinian evolution was provided by the highly influential Harvard geneticist Richard Lewontin, in an article entitled “The Units of Selection,” published in the Annual Review of Ecology and Systematics back in 1970. Here it is:

“As seen by present-day evolutionists, Darwin’s scheme embodies three principles …

1. Different individuals in a population have different morphologies, physiologies, and behaviors (phenotypic variation).

2. Different phenotypes have different rates of survival and reproduction in different environments (differential fitness).

3. There is a correlation between parents and offspring in the contribution of each to future generations (fitness is heritable).

These three principles embody the principle of evolution by natural selection. While they hold, a population will undergo evolutionary change.”

In schematic form: (Darwinian) Evolution = variation + diff. fitness + inheritance.

How does this square with the idea of thinking of cultural evolution as a Darwinian process? Well, clearly there is variation in cultural traits. To use again the examples we have already considered from the paper by Acerbi and Mesoudi, there is a pool of available names to be chosen for newborn babies; there are a number of stories like Cinderella (and different versions of that one story); there are both direct gaze and indirect gaze portraits; and so forth.

In terms of inheritance, however, we encounter the first problems. To begin with, when cultural traits are copied (baby names), then we have a fairly high fidelity analog of biological inheritance, even accompanied by the possibility of “mutations,” though a crucial difference is that many of these mutations will be the result of conscious choices by parents, not of random processes. That’s important, because it imparts an inherent bias, and hence possible directionality, to cultural evolution, which makes it already look quite different from its biological counterpart.

But if we are talking about the process of “reconstruction” involved in the phenomenon of cultural attraction (e.g., the retelling of the Cinderella story), then copy fidelity drops dramatically, and the resulting process looks even less Darwinian.

Finally, we have the issue of differential fitness. Here, I think, is where the most difficult problems come sharply into focus for the idea of a Darwinian cultural evolution, and for reasons similar to those that doomed memetics. Which cultural traits are fitter than others, in which cultural environments, and why? It is not good enough to simply say that the fittest traits are the ones that differentially “survive,” because that amounts to a circular definition of the process. Karl Popper famously said that if that’s all that Darwinism is, then it isn’t a scientific theory, but rather a “metaphysical research program.”

(Biological) Darwinism, however, avoids the charge because of something called functional ecology. We don’t just say that, for instance, the similar body shapes of fast swimming animals — be they fish or mammals — evolved over and over because they were fit. We have testable explanations, based on hydrodynamics, for why they were fit, and indeed fitter than possible alternatives. We don’t just say that plants capable of storing water in their modified leaves (so-called “spines” in cacti) are fitter in a desert environment. We know why they are fitter in those environments when compared to normal leaves and water storage organs present in plants from other environments.

And so on. It is this ability to functionally link biological structures to their fitness advantage that makes Darwinian theory a scientific, predictive, theory, as opposed to a plausibly sounding, but ultimately untestable, just-so-story.

The challenge for students of cultural evolution, then, is to come up with functional ecological explanations of why certain cultural traits are fitter than others in certain cultural environments. And they also need to clear up the issue above concerned with mechanisms of cultural inheritance.

Ultimately, it is still very much an open question whether we can develop a coherent Darwinian theory of cultural evolution, or whether it may be better to abandon the analogy with biological evolution and recognize that culture is a significantly different enough beast to deserve its own theory and explanatory framework. Of course, cultural evolution is still tied to biological evolution, for the simple reason that we are both cultural and biological creatures. But we may have a long way to go before untangling the two and arriving at a satisfactory explanation of how precisely they are related to each other.

MASSIMO PIGLIUCCI IS THE K.D. IRANI PROFESSOR OF PHILOSOPHY AT THE CITY COLLEGE OF NEW YORK. HIS BACKGROUND IS IN EVOLUTIONARY BIOLOGY AND THE PHILOSOPHY OF SCIENCE, THOUGH HE HAS RECENTLY DEVELOPED A KEEN INTEREST IN STOICISM. HIS MOST RECENT BOOK (CO-EDITED WITH MAARTEN BOUDRY) IS “PHILOSOPHY OF PSEUDOSCIENCE: RECONSIDERING THE DEMARCATION PROBLEM” (UNIVERSITY OF CHICAGO PRESS, 2013). HIS OTHER WRITINGS CAN BE FOUND AT PLATOFOOTNOTE.ORG.