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"OH WATERS, TEEM WITH MEDICINE TO KEEP MY BODY SAFE FROM HARM, SO THAT I MAY LONG SEE THE SUN." - Rig Veda
Overly simplified, this "tipping-point" model (originally introduced by G. E. Hutchinson in 1959, and then later popularized by Jim McKnight in 1997 and Edward Miller in 2000) posits that genes associated with homosexuality confer fitness benefits in their heterosexual carriers. If only a few of these alleles are inherited, a males' reproductive success is enhanced via the expression of attractive, albeit feminine traits, such as kindness, sensitivity, empathy, and tenderness. However, if many of these alleles are inherited, a "tipping point" is reached at which even mate preferences become "feminized," meaning males are attracted to other males. In explaining this model, Miller asked readers to imagine a genetic system in which there are five different genes that place an individual along a masculine-feminine continuum. Each of the five genes has two alleles, one that pulls the individual to the masculine side and one that pulls to the feminine side. If a man inherited all of the feminine-pulling alleles (of which he has a 3.125% chance: .55), he will become homosexual. If he inherited less than all five of the feminine-pulling alleles, however, he would not be homosexual. Although originally proposed in simple form in 1959, this model was finally empirically tested in 2008 and 2009.
Behavioral geneticists at the Queensland Institute of Medical Research lead by Brendan Zietsch (joined by sexual orientation expert Michael Bailey and evolutionary geneticist Matthew Keller) found that psychological femininity in heterosexual men elevated the number of opposite-sex sexual partners, suggesting that their femininity was often attractive to women (think Johnny Depp). In addition, these researchers and those at Abo Akedemi University in Finland (lead by Pekka Santtila) independently predicted that if the "tipping point" model was correct, then heterosexual men with a homosexual twin should have more of the attractive feminine-pulling alleles and thus more opposite-sex sexual partners than members of heterosexual twin pairs.
"This study is part of a larger, worldwide comparative research effort to define the factors that gave rise to the first societies that developed public buildings, widespread religions and regional political systems — or basically characteristics associated with ancient states or what is colloquially known as 'civilization.' War, regional trade and specialized labor are the three factors that keep coming up as predecessors to civilization."