Why Sex Is Good by Clyde Freeman Herreid

Part II—Is It Always Good?

In a world without sex there would be no males and females. No flowers, no insects specialized in pollinating them, no extravagant colour and form like the peacock’s tail; and much animal behaviour would not exist. —Rolf Hoekstra

All of that is true, but so what? Who needs this stuff that Hoekstra is talking about for survival?

The great German biologist August Weismann proposed an answer to the question of “Why sex?” He asserted that sex increases genetic variation. When two different individuals mate by joining their gametes together, they produce a brand new genetic mixture and this promotes evolutionary adaptation.

This idea held sway for a hundred years until a couple of authors, George Williams and Maynard Smith, said, “Hold on. There are a couple of problems with this scenario.” Sex is not always good.

Mixing of the genes tends to break up favorable combinations. Why break up a good thing?
Asexual reproduction is twice as efficient as sexual reproduction at sending one’s genes into the next generation. Every time a sexual mother produces a child, that child only has one-half of the mother’s genes; the other half is from dad. An asexual mother reproducing parthenogenetically would give her child the complete set. In fact, it is better to have every individual in a population capable of reproduction (i.e., be a female) than to have individuals who are not (i.e., be a male). Such populations should rapidly out-reproduce a sexual population. This has been called the “two-fold cost of sex.”

On both of the above counts, it seems clearly disadvantageous for individuals to reproduce sexually! Yet sex has evolved and seems here to stay.

Many scientists have tried to puzzle their way out of this dilemma by testing some of the assumptions inherent in the argument.

Question

Can you design a way to test the hypothesis that asexual reproduction leads to a higher evolutionary fitness (i.e., leads to more progeny) than sexual reproduction?

Go to Part III—“Sex and Stress”

Originally published at http://www.sciencecases.org/birds_and_bees/birds_and_bees2.asp