Question

these extant primates have the greatest amount of sexual dimorphism, with males being 4 times the weight of females?

Gorillas

cebids

Humans

Lemurs

Answer 1

Answer: Sexual body size dimorphism is correlated with intermale competition and mating, counteracted by fecundity selection on the other sex. Species with monogamous mating system tend to show little or no dimorphism while those with polygynous mating systems, where intermale competition is high, exhibit higher dimorphism.

Extant primates exhibit broad range of variation in sexual body size dimorphism. It ranges from species such as gibbons and lemurs in which male and females have almost the same body sizes to species such as chimpanzees and bonobos in which male body size is larger than female. In humans, the body size dimorphism (male/female ratio) is on average 1.15, though it may vary to an extent. Gorillas, chimpanzees, bonobos and orangutans all exhibit sexual body size dimorphism, but to a different extent. The gorillas have the greatest amount of sexual dimorphism, having male/female body weight ratio of about 4 times. Orangutans also show high sexual dimorphism (male/female ratio is 2.23). In case of chimpanzees and bonobos, the ratio is moderate (1.29 and 1.36 respectively). In gorillas and bonobos, the dimorphism is due to differences in the duration of growth in the two sexes, where the male continues to grow for longer duration as compared to females. Some extant primates belonging to cebidae such as marmosets, tamarins, etc however characterized by the reverse dimorphism, in which females are larger than males. In case of Lemurs, the females dominance over males accounts for the reverse dimorphism.