The Limits Of Darwinian Reasoning

Darwin is the man, and like so many biologists, I have benefited from his prescient insights, handed to us 150 years ago. The logic of adaptation has been a guiding engine of my research and my view of life. In fact, it has been difficult to view the world through any other filter. I can still recall with great vividness the day I arrived in Cambridge, in June 1992, a few months before starting my job as an assistant professor at Harvard. I was standing on a street corner, waiting for a bus to arrive, and noticed a group of pigeons on the sidewalk. There were several males displaying, head bobbing and cooing, attempting to seduce the females. The females, however, were not paying attention. They were all turned, in Prussian solider formation, out toward the street, looking at the middle of the intersection where traffic was whizzing by. There, in the intersection, was one male pigeon, displaying his heart out. Was this guy insane? Hadn’t he read the handbook of natural selection. Dude, it’s about survival. Get out of the street!!!

Further reflection provided the solution to this apparently mutant, male pigeon. The logic of adaptation requires us to ask about the costs and benefits of behavior, trying to understand what the fitness payoffs might be. Even for behaviors that appear absurdly deleterious, there is often a benefit lurking. In the case of our apparently suicidal male pigeon, there was a benefit, and it was lurking in the females’ voyeurism, their rubber necking. The females were oriented toward this male, as opposed to the conservative guys on the sidewalk, because he was playing with danger, showing off, proving that even in the face of heavy traffic, he could fly like a butterfly and sting like a bee, jabbing and jiving like the great Muhammed Ali.

The theory comes from the evolutionary biologist Amotz Zahavi who proposed that even costly behaviors that challenge survival can evolve if they have payoffs to genetic fitness; these payoffs arrive in the currency of more matings, and ultimately, more babies. Our male pigeon was showing off his handicap. He was advertising to the females that even in the face of potential costs from Hummers and Beamers and Buses, he was still walking the walk and talking the talk. The females were hooked, mesmerized by this extraordinarily macho male. Handicaps evolve because they are honest indicators of fitness. And Zahavi’s theory represents the intellectual descendent of Darwin’s original proposal.

I must admit, however, that in recent years, I have made less use of Darwin’s adaptive logic. It is not because I think that the adaptive program has failed, or that it can’t continue to account for a wide variety of human and animal behavior. But with respect to questions of human and animal mind, and especially some of the unique products of the human mind — language, morality, music, mathematics — I have, well, changed my mind about the power of Darwinian reasoning.

Let me be clear about the claim here. I am not rejecting Darwin’s emphasis on comparative approaches, that is, the use of phylogenetic or historical data. I still practice this approach, contrasting the abilities of humans and animals in the service of understanding what is uniquely human and what is shared. And I still think our cognitive prowess evolved, and that the human brain and mind can be studied in some of the same ways that we study other bits of anatomy and behavior. But where I have lost the faith, so to speak, is in the power of the adaptive program to explain or predict particular design features of human thought.

Although it is certainly reasonable to say that language, morality and music have design features that are adaptive, that would enhance reproduction and survival, evidence for such claims is sorely missing. Further, for those who wish to argue that the evidence comes from the complexity of the behavior itself, and the absurdly low odds of constructing such complexity by chance, these arguments just don’t cut it with respect to explaining or predicting the intricacies of language, morality, music or many other domains of knowledge.

In fact, I would say that although Darwin’s theory has been around, and readily available for the taking for 150 years, it has not advanced the fields of linguistics, ethics, or mathematics. This is not to say that it can’t advance these fields. But unlike the areas of economic decision making, mate choice, and social relationships, where the adaptive program has fundamentally transformed our understanding, the same can not be said for linguistics, ethics, and mathematics. What has transformed these disciplines is our growing understanding of mechanism, that is, how the mind represents the world, how physiological processes generate these representations, and how the child grows these systems of knowledge.

Bidding Darwin adieu is not easy. My old friend has served me well. And perhaps one day he will again. Until then, farewell.