From National Geographic‘s “The Third Sex“:

In Thailand the concept of three sexes is ancient. Creation tales from northern Thailand say that in the beginning, a man and woman had three children: a male, a female, and a third sex. Many Thai believe that to be born a ladyboy or ‘phuying praphet song’—literally translated, ‘second kind of woman’—is a result of one’s karma. Many believe that in their past lives, ladyboys were men who had many affairs with different women. It was their karmic destiny to be reincarnated as a woman trapped in a man’s body. Ladyboys believe that if they behave well they will be reborn as either a man or woman.

Thailand’s estimated 180,000 ladyboys might live as women, but legally they are considered men.

Check out Thailand’s Third Sex gallery by Kevin Tat.