Wednesday, April 05, 2006

Answer to Anna's Question

An inciteful friend of mine, asked me a question the other day, and though I understood the answer, I couldn't quite explain it the way she deserved to hear it. The way to explain it came to me today, and I thought it worthy of a blog entry:

Q:Why is there such a disparity between the amount of resources that each sex puts into their offspring? Why does it seem that females get the short end of the stick?

A:To put it bluntly, males are selfish mutants. Here's why:

Imagine a species where there is no difference at all between the sexes, in fact there would be no reason to distinguish them as two different sexes. They still reproduce sexually but the sex cells split evenly in both parents and both parents swap them and both get pregnant. The resources for reproduction would be shared evenly between the 2 parents, both would have to deal with the costs of gestation and rearing. Now imagine that a selfish mutant comes into the population and decides it only wants to inseminate but not be inseminated because it doesn't want to invest the resources and time required for gestation. Because of this, this selfish mutant can spend the time it normally would gestating getting other organisms pregnant. In the next generation of these organisms the selfish mutant genes will have higher numbers than any one of the non-selfish ones. This generation with a higher population of selfish mutants will produce even more selfish mutants in the next generation. However, since these mutants can't get pregnant, the proportion of mutants to non-mutants will quickly rise to 50% and stay there unless there are other external factors at play. This is what's called an evolutionarily stable strategy.

Populations of individuals need to find strategies that maintain the population without having to be disrupted by an even more selfish individual happening upon them. Many of the breakthroughs associated with modern biology come from this line of reasoning. It was first proposed by John Maynard-Smith and has since been a powerful tool in understanding animal behavior.

If this piques your interest I highly recomend Richard Dawkins's the Selfish Gene.

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