When I was a zoology student, I was taught that this was the male’s biological imperative, written not in stone but in gametes. Anisogamy – the fundamental difference in gamete size, from the Greek, meaning ‘unequal’ and ‘marriage’ – is said to define not just the sexes but also their behaviour. Sperm are small and bountiful, whereas eggs are large and limited; so males will be promiscuous and females will be choosy and chaste.
