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 in general they evolved to give an individual an advantage over its rivals in courtship. They are opposed to the primary sexual characteristics: the sex organs.

In humans, secondary sex characteristics include:

• Male
  • more abdominal hair
  • more chest hair
  • more facial hair (beard)
  • on average, larger hands and feet than women
  • broader shoulders and chest
  • heavier skull and bone structure
  • greater muscle mass and physical strength
  • a prominent Adam's apple and deep voice
  • fat deposits mainly around the abdomen and waist (apple shape)
  • coarser skin texture

• Female
  • 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, thighs and hips (pear shape)
  • smoother skin texture

Sexual differentiation begins during gestation, when the gonads form. General habitus and shape of body and face, as well as sex hormone levels, are similar in prepubertal boys and girls. As puberty progresses and sex hormone levels rise, differences appear.