Humans are the only primate species in which mammary glands (breasts) remain large and prominent throughout adulthood.

Humans are the only primate species in which mammary glands (breasts) remain large and prominent throughout adulthood. Other primates’ mammary glands swell only when they are nursing offspring; scientists are not sure why human females have noticeable breasts on a permanent basis. One hypothesis is that they increase a female’s ability to attract mates. If so, this would be an example of a trait favored by…