Study: males with an extra female sex chromosome may have increased libidos

A study published in the journal, Hormones and Behavior, has found evidence of a gene on the X chromosome in mammals that may cause an increased libido in males.

Gender in mammals is determined by the sex chromosomes X and Y. An XX combination results in a female while an XY produces a male. However, some individuals are born with an XXY combination. In humans this occurs about one in every 500 to 1,000 births and is known as Klinefelter's syndrome. Individuals who have this syndrome have male genitalia, but they are infertile and have decreased testosterone levels. One might expect that these individuals also have a decreased sex drive, but the opposite appears to be true.