CoachNatural selection is the difference in reproduction between individuals that carry different alleles, in a given environment: the carriers of one allele leave, on average, more descendants than the carriers of another, and the allele’s frequency rises from generation to generation. What is selected is the whole individual — its survival, its mating, its fertility — and the alleles ride along.
Examples
Example 25.6 (Selection by the other sex)
A peacock’s train makes it slower and more visible to predators, yet it is kept because peahens choose the males with the largest and most regular trains: an allele that improves the train is passed on more often, whatever it costs in survival. Sexual selection — the choice of mates — produces the ornaments, songs and contests of animals, and can push a trait in a direction that survival alone would never favour.