Why Sexual Selection is a Bitch

Sexual selection is the term that defines the fact that in nature, often fit and sexy men are more likely to become fathers. This is shown in many different ways. The most well known example would be how two males fight, and the winner, being stronger or faster, or simply fitter, gets to mate with all the ladies, while the looser has to move on without getting lucky.

This is a good mechanism as this promotes strong, fast, fit genes to be passed on to the next generation and therefor keeping the overall population strong, fast and fit.

But sexual selection also works in a different way. Being, that sexy, good-looking men are more likely to get lucky and reproduce. And this is where the bitch comes in: Some male birds, and I would like to use the long-tailed paradise whydah (Vidua paradisaea) as an example here, grow extremely long tail feathers in an attempt to woo the ladies and they do indeed look very dashing during mating season.

However, the tail feathers are so large, that they have trouble staying airborne when flying. This results in a rather funny flight pattern of a bird flapping his wings hard to get up and soon sinking down pulled by the weight of his tail. This of course makes them vulnerable to predators (natural selection). So here natural selection holds balance with sexual selection, making sure that the men are sexy, but still functional enough to survive.

There are theories that one reason the mammoths went extinct, is that lady mammoths found large tusks to be very sexy, causing an increase of tusk size over the generations. This, so goes the theory, went so far, that the tusks prevented them from being able to eat properly and made them clumsy when defending themselves from predators, bringing upon them the downfall of the species. That theory is probably false. Today the prevailing theory is that mammoths (by the way, there were several species and their stories are different) went extinct due to climate change and the resulting disappearance of their habitat after the ice age 12000 years ago. And humans deal with it too: According to one study sexual selection is one reason why the Dutch people are so tall. The tallest in the world actually.

Source:

Enserink, M: Did natural selection make the Dutch the tallest people on the planet?  Posted 7 April 2015 on  Sciencemag.org.doi:10.1126/science.aab2453