genes

Richard Pillard (pictured) - professor of psychology in the Boston University School of Medicine - has been doing research which suggests a strong biological basis for sexual orientation.

Pilliard said through his research and personal experiences, he believes there may be a genetic basis for sexual orientation and the origin is "prenatal, partially genetic just like heterosexuality."

Why haven't gay people gone extinct? Because gays and lesbians nurture their nieces and nephews in order to help their family grow. The bigger the family - the higher likelihood of having gay relatives.

A new study found that gay men may be predisposed to nurture their nieces and nephews as a way of helping to ensure their own genes get passed down to the next generation.