Since the Human Genome Project was completed in 2003, many theories based on the findings (or lack thereof) have come to light. The Evolution Sex Theory states that humans are given genetic instructions to be male or female and to have sex with the opposite sex in order to reproduce. Though it's not fully understood how, these traits are thought to promote the genes that carry them. < http://paleodiet.net/Sex_Gene.html >
This theory is based strictly on the 253 million base pairs of the genes contained within the X chromosome and Y chromosome. <http://www.trueorigin.org/gaygene01.asp >