Accelerated speciation:
Received wisdom is that the beautiful (or ridiculous if that is your bent) ornamentation of the peacock is the result of the tastes of the peahen. It makes simplistic sense. The females mate with males. The males display their charms. There must have been a runaway evolution with an extreme result.
That works just fine until you actually look at some birds. Here are some people and some peafowl. A peahen is casually pecking for bits of food, either authentically or in thespian mode uninterested in anything else. A peacock struts up, zeroes in on her, displays his iconic tail, shakes it until it rattles and looks really impressed with himself. The humans take far more evident interest in the display than does the peahen. She is anything but driven into instant sexual frenzy.
There are biologists who hold that the tail is a demonstration of the fitness of the male. It takes a lot of good genes and good nutrition to make one, so he must be a good catch. But that means the tail evolved precisely because it reduces fitness. And her male offspring will suffer the same penalty.
So there is at least a theoretical reason for the tail. The female likes it, all appearances to the contrary. Well that theory is testable. We go back in time and look at the first peafowl. Were the males drab? In that case we should acknowledge that something, probably the peahen population, has rewarded increased conspicuity.
But in the absence of this, admittedly impractical observation, one must wonder what else could be going on.
Here’s an idea. Speciation is of course of enormous interest because it is the mechanism of speciation that drives the development of the mechanism of reduced fertility with reduces consanguinity.
Borrowing from the work of Alfred Russell Wallace, a British man who would have scooped Darwin on evolution by natural selection had Darwin not had the funds and the audacity to publish his book before the less wealthy Wallace could, speciation is very important. And, if memory serves, one of the first things that an animal form must do when presented with a new ecological niche is to undergo speciation so that it can effectively get selected for traits that will optimize it for the new opportunity. Call it the Wallace effect if you need a name. With peafowl, then, there is early on enormous pressure to develop a display that says not, “I am a really sexy, really fit peacock,” but rather, “It’s all right. I’m a peacock.” As Aristotle says, your teeth weren’t made for your convenience. They happened by chance and they persist because they work. So once the display worked, it persisted. Sex, peace you philandering liberals, is very conservative. But quite possibly if we looked at early peacocks their ornamentation would be more striking, not less striking, than what we see today.
There is a clue. (Andrew F. Hugall and Devi Stuart-Fox Accelerated Speciation in Colour-Polymorphic birds NATURE vol. 485 no. 7500 May 31, 2012 page 631) Looking at species of birds that vary greatly in their appearance, it turns out that those that very more can undergo speciation faster. And once speciation is accomplished the variability declines. Now losing an optional appearance is not exactly the same as losing the intensity of an appearance, but it would seem that the two processes are a bit similar.
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