Recently there have been a number of posts and comments on evolutionary psychology. A new paper in PLoS Biology argues that human brain evolution since the “stone age” (really?) has been rapid and multifaceted. And there are renewed calls for evolutionary psychology to change. As usual, John Hawks has a good commentary.
Criticisms of evolutionary psychology have been around for a long time and the criticisms and program offered by Johan Bolhuis and colleagues are not in themselves new. We shouldn’t just assume selection has occurred (although as Hawks notes, simply identifying that populations have grown is not evidence that selection has occurred). But what, exactly, should evolutionary psychology consist of? What should it do?
I think that the problem with evolutionary psychology (EP) is relatively shallow. After all, if we do have species typical (or population typical) behaviours, then they have to have evolved, and this will involve some adaptations. Something like EP must be right. The problems with EP are not unique to EP, but to studies of adaptive behaviour across the board. It is in effect the role that selection itself plays. It’s almost as if because it is evolutionary, it must be natural selection, but as the very founder of the modern Synthesis, R. A. Fisher, wrote in 1930, in the first sentence of his seminal work, The Genetical Theory of Natural Selection, “Natural Selection is not Evolution”. Why? Because selection can cause or retard evolution, and it can cause diversity or cohesiveness in a species or population. Natural selection is, well, it’s natural selection, and as I have argued, it’s not even a mechanism, but an explanatory scheme into which actual mechanisms are placed. The obsession on natural selection is, I think, unwarranted.
Without methodologies (which do exist and are highly mathematical) that can distinguish natural selection from other dynamics of traits in populations (such as ordinary population growth), to call some trait “adaptive” rests very largely on a subjective judgement. Since we are all liable to confirmation bias, we can find things adaptive this way that are simply reinforcing our prior prejudices (in the sense of “pre-judgements”) that some behaviour or trait is the natural outcome of things.
EP is merely the latest incarnation of sociobiology, or social biology, a research program that has been going on since the 1860s (W. R. Greg’s work is mentioned in Darwin’s Descent of Man, ambiguously). Sociobiology, since its inception, has made analogies from distantly related species to ourselves: stamping grounds are the mating grounds of antelope, so why apply them to humans? Pecking orders were observed in flocking birds like chickens, so why apply them to humans? and so on. The initial sociobiology was massively based on analogies chosen because they explicitly or subconsciously supported some prejudice regarding the “normal” social order of humans as understood by 1950s white western males.
We simply cannot divorce our sociobiology from our cultural biases, no matter how hard we try. Not even the most feminist inclined cultural relativist will be able to do this as an act of will. So even though our psychological dispositions evolved, and much of it evolved by adaptation through natural selection to environments, it looks like evolutionary psychology is fated to fail. Or is it?
I want to suggest that if we stop trying to force everything human into the natural selective straitjacket, we might be able to do some EP that is not subjected to as much arbitrary prejudice. The solution is, I think, to ensure that the traits being discussed are not analogised with relatively unrelated traits in other species, but instead to those traits that are closely related, but are in nonhuman species we are more able to separate from our socialised prejudices. In short, Sociobiology Mark 3 should be phylogenetic.
Sociobiology Mark 1 was promiscuously analogous. Sociobiology Mark 2 was hyperadaptationist. Perhaps Mark 3 can step back a bit from these extremes, and in the process learn something about ourselves by studying our relatives. Cultural biases apply less when you are considering the sociobiology of a gibbon, a baboon or a macaque. What is it we have in common with out relatives because they are our relatives and not because they match our prior beliefs about ourselves or the presumption that all evolution is selective?
In phylogenetic systematics (ofen called “cladism” perjoratively), a trait that is shared among members of a monophyletic group (a “clade”) is a homology. It may be shared unchanged (a plesiomorphy) or changed in different taxa (an apomorphy). Both are homologies. Now even when a homology is changed in some species or other, it remains identifiable as a homology. Consider that the third digit of a bird is homologous with the third digit or, say, a human hand, even though they are not very similar in form, function, or size relative tot he rest of the skeleton. We can identify it because it is in the “same” place in development, and draw some conclusions from that based on our overall knowledge of the developmental processes all vertebrates share.
Behaviours are, if inherited by taxa over evolutionary times, homologies too. Each species has its own typical behaviours, which are modulated by environment, culture and contingencies of individual development, but we nevertheless can identify that there is a species-typical mating strategy for gorillas, bonobos and baboons, which is unique in each case but homolgous across the primate family. Likewise, social organisation. We can identify what is common to all members of Primata, and since we are members of Primata too, what is common to us. Once we do that, we can start to look at the ways in which we are unique for those homologies.
For example, our mating strategy is not at all like the dominant male polygyny of gorillas, nor is it much like the polygynandry of the bonobos. Instead, we tend to pair-bond, at least serially, with some sneaky mating. Yet, the underlying biology is much the same – we have strategies to maximise the number of progeny we successfully rear because, well, that’s what evolution requires to continue. Every primate species is social, and every sexual strategy or mating system is designed around the unique traits of the species which are themselves traits adapted to the mating system. The massive sexual dimorphism of gorillas, where an alpha male silverback can outweigh an adult female 2:1 or more, is because competition for mating is fierce and solitary males will challenge for opportunities to mate that are almost (but not quite) all-or-nothing. Some sneaky mating occurs, of course, but even that is fraught with dangers. A silverback’s backhand blow can rupture internal organs.
So humans canot draw analogous inferences from gorillas, chimps or bonobos, our nearest relatives. But we can identify what sorts of behaviours are mating strategies and social organisation by looking at what varies between our sister taxa. This might seem obvious, but only in retrospect. Most of the work done on primate sneaky mating is done on nonhuman primates. Once we identify what the issues are, then we can identify them in humans with less cultural bias. [Incidentally, I hypothesise that overall, the ratio of sneaky matings to “legitimate” matings among primates will be roughly the degree of dimorphism – the closer in size males and females are, the less sneaky mating occurs. Bonobos, whose sexes are almost identical in size, do not compete for mating opportunities because they share territory and are polygynandrist. Humans are likely less sneaky maters than gorillas. I may be wrong about that.]
As I have argued before, a natural classification by homology permits inductive inferences in the absence of specific information about a species. One has a kind of epistemic Chinese Wall, in which one can act as if one knows nothing about the species (in this case, our own) to begin with, and set up the sorts of expectations we might have knowing what we do about the rest of the clade. This is an old strategy, shorn of the phylogenetics. Before Oliver Sachs used the term, Alfred Wallace referred to himself as the “Anthropologist on Mars” when considering humans, and Desmond Morris began his Naked Ape with a similar argument. But employing phylogenetics means that we can do this with some degree of dispassion other than subjective abilities. Then we can look at how these traits are realised, not only in the species as a whole, but in regional populations and subcultures. Phylogeny can act as a contrast space for our investigations.