While a ratio of one male to one female is a prevalent human experience through the human mechanism of reproductive-type sex, other sex ratios probably also have a biological basis. Different sex ratios are possible for human sex that encompasses sex not of reproductive type. Roughgarden (2004), in an important challenge to the standard Darwinian story of evolutionary typically taught in schools and universities, argues competition to have reproductive-type sex does not adequately account for the scientific evidence of diversity of biological sexual forms and sexual behaviors. Roughgarden, like Genesis 2:23-25, emphasizes that sex has a unitive as well as procreative purpose.