Evolutionary accounts of deductive reasoning have been enjoying a fair amount of popularity in the last decades. Some of those who have defended views of this kind are Cooper, Maddy, and more recently Joshua Schechter. The basic idea is that an explanation for why we have developed the ability to reason deductively (if indeed we have developed this ability!) is that it conferred a survival advantage to those individuals who possessed it among our ancestors, who in turn were reproductively more successful than those individuals in the ancestral population who did not possess this ability. In other words, deductive reasoning would have arisen as an adaptation in humans (and possibly in non-human animals too, but I will leave this question aside). Attractive though it may seem at first sight (and I confess having had a fair amount of sympathy for it for a while), this approach faces a number of difficulties, and in my opinion is ultimately untenable. (Some readers will not be surprised to hear this, if they recall a previous post where I argue that deductive reasoning is best seen as a cultural product, not as a biological, genetically encoded endowment in humans.)
In this post, I will spell out what I take to be the main flaw of such accounts, namely the fact that they seem incompatible with the empirical evidence on deductive reasoning in human reasoners as produced by experimental psychology. In this sense, these accounts fall prey to the same mistake that plagues many evolutionary accounts of female orgasm, in particular those according to which female orgasm has arisen as an adaptation in the human species. To draw the parallel between the case for deductive reasoning and the case for the female orgasm, I will rely on Elisabeth Lloyd’s fantastic book The Case of the Female Orgasm (which, as it so happens, I had the pleasure of re-reading during my vacation last week).