The advantage of sex.

Fifty per cent is a large cost. The problem of explaining sex is to find a compensating advantage of sexual reproduction that is large enough to make up for its cost.

The problem is not trivial. Indeed, G.C. Williams has described it as

"the outstanding puzzle in evolutionary biology".

However, several possible advantages of sex have been suggested. Before discussing them in detail, the following Virtual Experiment allows you to form your own ideas.

Imagine an organism that is able to reproduce either sexually or asexually - many such organisms exist, such as strawberry plants pictured opposite. A population of such organisms is simulated, and the proportion of reproduction that is sexual can be given as an input value before the experiment is run.

Fitness is calculated from the value of some character under selection. What are the effects on changes in mean fitness of different proportions of sexual reproduction? What might cause these results?