This is a reproduction of the map made by Luigi Luca Cavalli-Sforza in his book The history and geography of human genes. It displays the genetic relationship between human populations. (Photo credit: Wikipedia)
The principle thesis of gene-culture coevolution (a.k.a. dual-inheritance theory) is that genes and culture both contribute to evolution in the case of humans. Luca Cavalli-Sforza and Marc Feldman at Stanford led the way in this field, and were later joined by Robert Boyd and Peter Richerson at UCLA. To determine precisely the relative contributions of genes and culture, these researchers began to create highly technical, detailed mathematical models.
Cultural selection vs. natural selection
Coevolution begins with a distinction between cultural selection, which operates by the differential replication of the meme, and natural selection, which affects culture by the differential reproduction of a meme’s host as a consequence of having it (Cavalli-Sforza & Feldman, 1981). These concepts clearly distinguish two different mechanisms by which cultural entities, including religions, may change.
Durham (1991) expands on this by identifying at least five ways in which these mechanisms interact. The first two are genetic mediation, whereby cultural variation is driven by genetic differences, and cultural mediation, in which cultural differences drive genetic evolution. The latter has been used to explain the spread of genes for lactose absorbance among Europeans due to the cultural habit of dairy farming (Durham, 1991). The other three interactions, enhancement, neutrality, and opposition, are similar to Dennett’s three symbiotic relationships: mutualist, commensal, and parasitic, respectively. In these five ways, genes and culture interact to produce human behavior.
Guided variation
As for the means by which memes change, analogous to mutation among genes, Boyd and Richerson (1985) propose guided variation, or the process by which cultural information about a behavior is received and then modified by the individual on the basis of personal experience. This concept seems to fall short of the mark, however, as it begs the question of what causes the individual to make these modifications. A more thorough meme’s-eye view interpretation might posit that modification decisions result from competition and interaction among memes within the individual’s mind, as part of the normal processes that constitute human consciousness. Indeed, Dennett has proposed that consciousness may be none other than the result of memes modifying their environment, i.e. the human mind, to better suit their needs (Dennett, 1993).
Biased cultural transmission
In any case, variation exists among memes, and certain forces influence choice between alternatives. This is called biased cultural transmission (Boyd & Richerson, 1985), which comes in two types. First, direct bias predisposes the individual to prefer certain types of information, “based on their judgments about the properties of the variants themselves” (Boyd & Richerson, 1985). This may well result from genetic adaptation resulting in innate psychological predispositions, as theorized by evolutionary psychology. It may also result from other means, such as prior integration of certain memes modifying reception of other memes. For example, someone who has accepted the Creationism meme will thereafter prefer memes consistent with that worldview. The other type of biased transmission is indirect bias, a.k.a. frequency-dependent bias, whereby the probability of accepting a meme is influenced by its prevalence in the population. Humans have a tendency toward conformity, and this significantly affects the spread of memes in a group (Boyd & Richerson, 1985).
Group selection
This leads to yet another important concept in coevolution, group selection. This form of selection has been disfavored by biology for some time, but recent studies suggest it may play a greater role than previously thought. The main problem is that group selection requires that traits of individuals within a group remain relatively consistent over time, but within-group variation destabilizes these traits, such that group selection seems possible only under exceptionally rare conditions.
Boyd and Richerson (1985) propose that conformity provides the means by which within-group variation is overcome in the case of cultural evolution.
The next post will apply these concepts to the evolution of religion.
This post continues a series investigating methods in the study of religion from an evolutionary perspective. Various approaches will be considered in turn, and evaluated for their strengths and weaknesses.
