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Manus haec inimica tyrannis.

Tuesday, February 17, 2015

Consider the Peacock

I’ve been reading a book by Richard Joyce called The Evolution of Morality (Cambridge, MA: MIT Press, 2006). Now, I am far from a creationist (though I’m also far from a scientist), and in broad outlines I am a thorough believer in the theory of evolution and in some version of its mechanism of action, natural selection. Nevertheless, whenever I read a work in which the theory is applied to such complex human phenomena as our propensity to make moral judgments, I am usually left unsatisfied and sceptical.

I am left unsatisfied, because such explanations often seem beside the point: I’m never sure what purpose is served by an evolutionary explanation of how human morality arose. Is it somehow supposed to validate our moral judgments, by grounding them in our biology? If so, why is such validation necessary? Are we more apt to avoid theft if we are told that we are hardwired to find theft wrong? Or is it somehow supposed to debunk our moral judgments, by demonstrating that the experienced wrongness of theft is nothing more than a biological reaction that could have been otherwise if our evolution was just a little bit different, and that “theft” and “wrongness” are simply biological phenomena? Will this knowledge make me view my disapproval of theft as somehow contingent, parochial? In other words, I’m doubtful that an evolutionary “explanation” of morality would have much relevance for morality. It would simply be an entertainment for the curious, its entertainment value a function of aesthetic concerns such as the elegance, cleverness, and ontological economy of the explanation offered.

It must be said that Joyce’s book, to its credit, does a very good job of addressing (though not necessarily answering) the question of what purpose an evolutionary explanation of human morality is supposed to serve, or of what difference such an explanation would (or wouldn’t) make to morality itself, as practiced by humans. Indeed, this is probably the main strength of the book.

However, besides leaving me unsatisfied, evolutionary explanations of complex human phenomena also often leave me sceptical, because stories proffered to show how a certain faculty like morality arose almost always end up seeming just that — stories. Sometimes the stories are very clever, very elegant, very plausible, but for every such story on offer there is usually another writer with a different plausible story. With multiple just-so stories for sale, a reader can be excused for finding such stories dubious in general. And it seems the more complex the phenomenon being explained, the more alternative stories there are available to explain it.

Indeed, in some cases scepticism can result from explanations offered for quite simple phenomena. Take, for instance, the concept of sexual selection, as used to explain some of the more florid examples of seemingly maladaptive physical traits. Here is Joyce (p. 32) with a well-known example:

Consider the enormous and cumbersome affair that is the peacock’s tail. Its existence poses a prima facie threat to the theory of natural selection — so much so that Charles Darwin once admitted that the sight of a feather from a peacock’s tail made him ‘sick!’ Yet Darwin also largely solved the problem by realizing that the primary selective force involved in the development of the peacock’s tail is the peahen’s choosiness in picking a mate. If peahens prefer mates with big fan-shaped tails, then eventually peacocks will have big fan-shaped tails; if peahens prefer mates with triple-crested, spiraling, red, white, and blue tails, then (ceteris paribus) eventually peacocks will sport just such tails. Sexual selection is a process whereby the choosiness of mates or the competition among rivals can produce traits that would otherwise be detrimental to their bearer.

Now, at first sight nothing seems simpler than this explanation: peahens developed a sexual preference for males with large tails, and given this preference, peacocks with large tails were more likely to be chosen as reproductive partners, giving them a reproductive advantage over their smaller-tailed rivals. The story neatly answers a basic problem: why would an animal develop a trait that is so obviously an obstacle to its viability?

And yet, when we begin to inconveniently think too much about it, it doesn’t take long before the story starts to seem shaky. The problem to be solved by this story:

“Why do male peacocks have cumbersome tails that ought to make them less likely to survive long enough to reproduce?”

is not really solved at all, but rather is replaced by a different problem:

“Why do peahens have a preference for males with a seemingly maladaptive trait like cumbersome tails?”

Put another way, all we have done is shifted the focus from one maladaptive trait (massive tail plumage) to another (sexual preference for massive tail plumage). I fail to see that anything has been explained at all.

Let’s imagine a related but rival species to peafowl — related in the sense that they are physically similar in most relevant ways and (importantly) are eaten by the same predators, rival in the sense that they share the same ecological niche, relying on the same nesting places and food sources, etc.  Let us call this species “dandybirds”. Now, let us further imagine that dandyhens have developed a preference for dandycocks with small, light tails and fast running legs. Which species do you think is more likely to flourish in this ecosystem in the long run, peafowl or dandybirds?

We don’t even have to go so far as to imagine a different species; we can instead imagine a peafowl population with a subset of peahens who have a perverse sexual preference for peacocks with small, light tails and fast running legs. Which population subset is more likely to flourish?

And of course, we could also imagine an alternative kind of peafowl population in which females don’t get to choose mates at all, but are instead chased down and captured by peacocks for forced mating. This would necessarily favour strong and fast peacocks, who would be more likely to reproduce than their slower, fan-tailed brethren.

There are just too many competing possible roads natural selection could have gone down more plausibly.

Now I suppose the teller of the just-so sexual selection story could always come back with a reply to the effect that this is simply the road natural selection did in fact go down. Dandybirds never existed, nor did the alternative sorts of peafowl mentioned. Instead, there were in fact only peafowl whose females — through random mutation or whatever — prefer peacocks with extravagant tails. In other words, a highly improbable (but possible) state of affairs came about randomly. I suppose such an “explanation” is no better (or worse) than “explaining” a gambler’s run of good luck by simply recounting the series of lucky rolls he has shot.

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