Who sounds stronger: James Earl Jones or Mike Tyson? Who do you think would win in a fight? Most of us might rather have Darth Vader narrate a documentary, but the smart money says that in an actual knockdown drag-out, bet on the guy who bit off Evander Holyfield's ear. But apparently not all evolutionary psychologists would agree.
A new paper published in the Proceedings of the Royal Society by Aaron Sell, Leda Cosmides, John Tooby and their colleagues argues that we humans have evolved a faculty for assessing people's physical strength—and indirectly, their fighting prowess—just from the sounds of their voice. The idea sounds provocative and has a certain prima facie credibility, but unfortunately, my assessment is that this amounts to just one more in the long line of speciously reasoned papers that gives evolutionary psychology a dubious reputation. Here's why.
First he starting premise of the study is that because natural selection would have favored strong fighting abilities among our ancestors, any individuals who could assess others' fighting prowess quickly would have had a big advantage: depending on their inclinations, they could then either hide from the strong, pound on the weak or mate with the muy macho. For most of us still recovering from Post Traumatic Playground Disorder, this may make intuitive sense. And the authors cite a variety of papers representing "[m]ultiple converging lines of evidence," all of which might support the assumption (though their support still sounds circumstantial and debatable to me). Nevertheless, it is still just an assumption, and one of which we should be suspicious precisely because it does conform so easily to our current social experience.
Sure, if one's view of early human evolution is dominated by "nature red in tooth and claw" concepts of competition, in which Fred Flintstone has to wrestle a sabertooth and punch out Barney Rubble before dragging Wilma away by the hair, fighting ability would unquestionably be a plus. But combativeness also has its downsides. People who are good at fighting may be more likely to be in fights, which means that they may be killed or disabled sooner on average than those with more moderate skills and aggression. If early humans hunted in groups with weapons, the best hunters might not actually be the strongest: they might do better by virtue of their leadership, their strategies, their ability to maintain peace in the tribe. Not to mention that the women might be looking for something other than fighting prowess in a mate.
None of these points disqualifies physical strength or fighting ability as an important selective advantage. But they do mean that one can't simply say that strength and fighting ability automatically constitute important criteria for our ancestors' success.
Next, the researchers focus on upper body strength as a proxy for fighting ability. They offer reasons why the two correlate reasonably, and I don't have any objection to using upper body strength that way. Bear in mind, however, that this strength is only a proxy: any statement the researchers ultimately make about the relation of the voice to fighting ability is no stronger than that connection.
So then the researchers asked test subjects to rank unseen speakers by perceived strength, and found that the subject were indeed adept at doing so, even controlling for height and weight, even if the voices were speaking foreign languages. In a further apparent corroboration of their hypothesis, the researchers also found that people were better at assessing the strengths of males' voices than females'—because, of course, it would have been so much less important to assess women's physical strength or combativeness. (Of course, if there had been no difference in the facilities for judging men's and women's strengths from the sound of their voices, that might have only established just how fundamental and important this capability must be. So....)
Yet, again, what do these results truly show? At best, they establish only that people's voices do provide good cues about how others may perceive their physical strength. But the leap from physical strength to an evolutionary just-so story about natural selection favoring people's abilities to make this discrimination is still a big leap. People's voices may correlate well with their perceived strength, but let's face it, people's voices correlate well with lots of characteristics that may also correlate (causally or otherwise) with fighting prowess. For example, perhaps our perceptions of others' strength also corresponds to our sense of their self-confidence, or their social standing. Those may or may not be driven in part by their physical strength; but one therefore doesn't know for certain which of many such traits might have figured into natural selection (if any did).
I might be inclined to give this study more benefit of a doubt if it did not fall so squarely in line with many other evolutionary psychology papers—including ones from Leda Cosmides and John Tooby—that gravitate back to support for a view of human origins that heavily emphasizes the overwhelming dominance of violent conflicts, aggressive hunter females, more passive females and other clichés. Almost every other exploration of evolutionary biology seems to turn up surprises hidden from us in part by our cultural blinders; and yet human evolutionary psychology usually seems to shore up the cultural status quo. Doesn't that seem the least bit suspicious?
I'll repeat something I've said before: I completely want to believe in evolutionary psychology. I fully believe that someday we will have a strong, sound science of evolutionary psychology that offers real insights into human behavior. I support and encourage researchers' efforts today to start making that science a reality. But unfortunately, right now, I don't think we know enough in detail about either human psychology or human evolution to produce very persuasive theories in this area.