Secondary sex characteristics are traits that distinguish the two sexes of a species, but that are not directly part of the reproductive system. Some have argued that they evolved to give an individual an advantage over its rivals in courtship. They are opposed to the primary sexual characteristics: the sex organs.

Secondary sex characteristics can give individuals an advantage over rivals in one of two ways. Either they can be used to defeat rivals in combat, or they can be used to attract members of the other sex. An example of the former is the antlers on deer; the male with the best antlers defeats his rivals, and thus gains access to the females of the group. An example of the latter is the peacock's tail; the male with the most impressive tail will woo more females than a less impressive male.

Other secondary factors have to do with the child-bearing role of the female.

In humans, secondary sex characteristics include:

  • Man
    • chest and abdominal hair
    • more hair on other parts of body
    • more facial hair
    • on average, larger hands and feet than women
    • deep voice
    • fat deposits mainly around the abdomen and waist (apple shape)
    • coarser skin texture
  • Woman
    • enlarged breasts
    • on average, lower height than men
    • wider in hips than in shoulders
    • less facial hair
    • functional mammary glands
    • more subcutaneous fat
    • fat deposits mainly around the buttocks and thighs (pear shape)
    • smoother skin texture