Sunday, February 27, 2011

Sexy Selection

I've been meaning to write this post for...well probably for weeks now. But here it is. Aren't you excited? I was looking at some pictures of funny looking ducks that could dive to some pretty extreme depths a while back. The males had all these weird feather tufts on their wings and a big crest-like feature on their heads. It all seemed like it would really get in the way of effectively moving underwater. I thought, for a split second, why on earth would these ducks have evolved features that seemed counter-productive to getting food?

Then I remembered: Oh, right. Sexual selection. Perhaps you've heard about this process before but thinking about it in that light reminded me of what a powerful process sexual selection is. Sexual selection is the process that runs parallel to natural selection but has to do with individual animals choosing their mates. This is why you end up with extreme sexual dimorphism (when the male and the female of a species look very different from one another) and why you end up with ridiculous features like crests and bright colors that seem like they would get the creature killed in its quest for survival. These features often do run counter to surviving and that is why I think sexual selection is such an interesting topic: it can and usually does overpower the processes of natural selection.

The most impressive forms of sexual selection are probably found in the birds. That picture that reminded me of its power was a duck but the classic example (stop me if you've heard this) is the peacock tail. I can remember my professor clearly stating that the peacock's tail does slow it down to the point where it becomes difficult to get away from its predators. And what are peacocks predators? Well they are native to India and what big carnivores live there? Tigers. One of the worlds most capable hunters. The process of sexual selection has created a feature, this tail, that slows an animal down even under the selection pressures being exerted by one of the worlds most exceptionally effective carnivores. Natural selection is constantly trying to shorten and lighten the tail so the poor male peacock can get away from hungry tigers. But those pesky peahens are always choosing the males that have the biggest tails (actually the statistic seems to be the most "eyes," the bright blue spots peacocks have on their tails, that females are interested in) to mate with. That selection dictates that no matter how slow it makes the males the ones with more eye spots and therefor larger and heavier tails are getting to reproduce. As long as they get to sexual maturity and mate with a female it really doesn't matter if they then end up as tiger lunch.

So the next time you're out in the backyard, when the spring finally comes back, you can look at those bright red male cardinals and their bold crests and wonder at how those features came to be in the face of the selection pressures of peregrine falcons and other would-be predators.

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