Immediately relevant to game theory are the sex
ratios in certain parasitic wasp species that have a
large excess of females. In these species, fertilized eggs
develop into females and unfertilized eggs into males.
A female stores sperm and can determine the sex of
each egg she lays by fertilizing it or leaving it
unfertilized. By Fisher's genetic argument that the sex
ratio will be favored which maximizes the number of
descendants an individual will have and hence the
number of gene copies transmitted, it should pay a
female to produce equal numbers of sons and daughters.
Hamilton, noting that the eggs develop within their
host—the larva of another insect—and that the newly
emerged adult wasps mate immediately and disperse,
offered a remarkably cogent analysis. Since only one
female usually lays eggs in a given larva, it would pay
her to produce one male only, because this one male
could fertilize all his sisters on emergence. Like Fisher,
Hamilton looked for an evolutionarily stable strategy,
but he went a step further in recognizing that he was
looking for a strategy.