As the next installment in my series on evolution psychology (see previous posts here and here), I thought that I would write about some thoughts on evolutionary modules. As should be obvious from previous posts, I have serious concerns about evolutionary psychology. Nonetheless, I don't want to repeat the knee-jerk criticisms that attended the rise of what you might call (and Symons (1989) did call) "Darwinian Anthropology." Like Anthropology more generally, I have found that the level of discourse in human evolutionary studies tends to be particularly low and this surely hinders progress toward our presumably shared goals of understanding human behavior, the origin and maintenance of human diversity, and how people respond to social, environmental, and economic changes.
In this spirit, I am taking seriously the idea of modularity. The concept of "massive modularity" seems to be pretty central to just about any definition of modern EP and it is one of the ideas that I see as potentially most problematic. A major question that naturally arises in the analysis of cognitive modularity is: what is a module? There are two senses of modularity that you find discussed in the EP literature. For a good review of this, see Barrett and Kurzban (2006). In his highly influential (1983) book, Fodor popularized the concept of a cognitive module. A Fodorian module is characterized by reflex-like encapsulation of critical functions. It is thought to be anatomically localized, inaccessible to conscious thought and has shallow outputs. Our senses and motor systems are examples of possible Fodorian modules, as are the systems that underlie language (Machery 2007).
In contrast to the Fodorian module is the second sense of modularity found in the EP literature, the evolutionary module. Like a Fodorian module, the evolutionary module is domain-specific or informationally encapsulated. That is where the resemblance ends though. Rather than being defined by a list of attributes, an evolutionary module is characterized by function. An evolutionary module is a domain-specific cognitive mechanism that has been shaped by natural selection to perform a specific task. There is no need here to specify their characteristic operating time, the shallowness of their outputs, or their anatomical localization.
Using engineering-inspired arguments about efficiency and design, the proponents of massive modularity suggest that the brain is really a collection of domain-specific modules. These modules drive not just the reflex-like actions of our sensory-motor systems but also govern higher cognitive processes like reason, judgment, and decision-making. The brain is not, as we typically conceive it, a single organ. Rather it is a collection of special-purpose information processing organs. Needless to say, such a position has been controversial. Among the notable critics are Jerry Fodor himself, who wrote a whole book with the sarcastic title (referring to Steve Pinker's (1997) book, How the Mind Works), The Mind Doesn't Work That Way: The Scope and Limits of Computational Psychology. Another notable critic is David Buller, the ostensible subject of my last two posts.
Barrett & Kurzban (2006) suggest that much of the controversy surrounding the EP concept of massive modularity arises from confusion over what is meant by a module in the EP sense. That is, critics are thinking about Fodorian modules when the advocates of massive modularity have something entirely different in mind. Maybe. I'm no expert, but the argument seems plausible for at least part of the controversy. I have my own issues with modularity but I will save that for the paper that I am writing (and for which these posts serve as sketches to hopefully help me get some thoughts straight).
One point that I will make here is a fairly orthodox criticism of modularity. In enumerating possible evolutionary modules, and noting that such modules require domain-specific input criteria, Barrett & Kurzban (2006: 630) include "systems specialized for making good food choices process only representations relevant to the nutritional value of different potential food items." Really? I'm not one to fall back on the weak "culture complicates things" argument, but I do think there are other things -- including ones potentially important for fitness -- involved in food choice than the nutritional quality of a potential foodstuff. Perhaps an anecdote is in order here.
A long time ago, my wife and I were taken out to a fancy Chinese restaurant in Kota Tua, Jakarta by a colleague who wanted to impress us with his esoteric knowledge of a variety of Asian cuisines. He took the initiative and ordered for the table a range of items including tripe, jellyfish, pig trotters, and chicken feet. For a variety of complex social reasons, we felt it was in our interest to not seem like naïve rubes from America. So, we ate everything unflinchingly and with smiles on our faces. These were not things we normally would have volunteered to eat (though we now regularly get jellyfish) but the social payoffs of eating these (at the time) unappealing items outweighed whatever distaste we may have experienced.
Clearly, this is a bit of a trivial example. I nonetheless think that it highlights an extremely important aspect of human decision-making. The optimal decision in a one dimensional problem may change when one increases the dimensionality of the problem, particularly when the elements of your (vector) optimand trade-off. Sometimes the optimal nutritional choice is not the optimal choice with respect to social or cultural capital. The person's foraging decision is presumably one that balances the various dimensions of the problem. In a less trivial example, this is what Hawkes, O'Connell and Bird and Bird are suggesting is going on with some men's foraging decisions (summarized in this review by Bird & Smith (2005)). According to their model, men make energetically suboptimal foraging decisions in order to signal their phenotypic quality to political allies and potential mates. Food choice is thus a decision that balances the potential costs and benefits of at least three fitness-critical domains (energetics, politics, and reproduction). The same logic can be applied to that other staple of EP, mate choice. What people say they want on pen-and-paper surveys is not necessarily what they get when they actually choose a mate. The problem is that one's choice of mate spills over into so many other domains than simply future reproduction. So it's not simply a matter of the ideal mate being out of one's league. Sometimes, people actually prefer a mate who does not conform to their ideal physical type.
At the very least, this point seems to require positing the existence of yet another module that integrates the outputs of various lower-level modules. Of course, this is beginning to sound more like a generalized reasoning process, the bane of EP.
There is another usage of the term "module" that I think may have some relevance to this whole discussion. In evo-devo, modularity refers to the degree that a group of phenotypic characters have independent genetic architecture and ontogeny. I will call this an "evolutionary ontogenetic module" (EOM) and contrast that with an "evolutionary cognitive module" (ECM) of EP. Sperber (2002), in his defense of massive modularity, actually discusses EOMs in passing. Pigliucci (2008) details the various, largely divergent definitions of modularity. I tend to think about EOMs the way that Wagner & Altberg (1996) do, wherein a modular set of traits is one with (1) a higher than average level of integration by pleiotropic effects (i.e., gene interactions) and (2) a higher than average level of independence from other trait sets. That is, modular architecture occurs where there are few pleiotropic genes that act across characters with different functions but more such effects falling on functionally related traits.
Modularity in the evo-devo sense is central to the evolution of complexity as well as the evolution of evolvability (the capacity of an organism to respond adaptively to selection). Do ECMs need to be EOMs? Does this and other related concepts from evo-devo help provide a means for relating the ideas of EP or HBE to their genetic architecture and ontogenetic assembly? I think so but I think an elaboration on this topic awaits a later post.
Barrett, H. C., and R. Kurzban. 2006. Modularity in Cognition: Framing the Debate. Psychological Review 113 (3):628-647.
Bird, R. B., and E. A. Smith. 2005. Signaling Theory, Strategic Interaction, and Symbolic Capital. Current Anthropology 46 (2):221-248.
Fodor, J. 1983. The Modularity of Mind. Cambridge: MIT Press.
Machery, E. 2007. Massive Modularity and Brain Evolution. Philosophy of Science74: 825–838.
Pigliucci, M. 2008. Is Evolvability Evolvable? Nature Genetics 9:75-82.
Pinker, S. 1997. How the Mind Works. New York: Norton.
Sperber, D. 2002. In Defense of massive modularity. In Dupoux, E. Language, Brain and Cognitive Development: Essays in Honor of Jacques Mehler. Cambridge, Mass. MIT Press. 47-57.
Symons, D. 1989. A Critique of Darwinian Anthropology. Ethology and Sociobiology 10 (1-3):131-144.
Wagner, G.P., and L. Altenberg. 1996. Perspective: Complex Adaptations and the Evolution of Evolvability. Evolution 50 (3):967-976.