Biology Lecture 15: Sexual Selection
Intrasexual vs. Intersexual Selection:
o Intrasexual selection: competition between the same sex
o Intersexual selection: female choice, a trait is considered attractive in a male
Females often picker than males. Why?
o Males are competing for access to females
Anisogamy = unequal gamete size:
o Females produce relatively small number of large nutritious gametes (eggs)
o Males produce a larger number of small gametes without much nutritional reserve (sperm is
o Sex differences in parental investment determine which sex is choosy, and which sex
Selective forces on males vs. females:
o Average fitness of males is equal to the average fitness of a female.
o Males have a higher potential fitness (Moulay Isamael - 888 children) than females (Mrs.
Vassilyev - 69 children)
o Male potential fitness is determined by how many mating opportunities they can find
o Females tend to be limited by access to resources (eggs)
Different selective forces acting on males and females