I just read an interesting snippet in The Monitor on Psychology. It cited research that found that heterosexual males and females differed from each other in terms of jealousy, where as bisexual men and women and gay men and lesbians did not differ in their jealousy. The researchers looked jealousy being triggered either by (1) sexual infidelity without emotional attachment and (2) emotional attachment (emotional infidelity) without sexual activity. They found that heterosexual men became more jealous in response to sexual infidelity and heterosexual woman became more jealous in response to emotional infidelity.
The results differing heterosexuals was not surprising; the theory of evolutionary psychology predicts that behavior that assures that the offspring carry on the male’s genes–and are attending to through the female’s efforts–is important to the male. Additionally, the prediction for females would be that females are more concerned about the male assisting in supportive resources–more so than the male’s genes necessarily–which would be threatened by an outside attachment.
However, I have never seen anything in evolutionary psychology theory that would suggest that this orientation toward threat would not translate for non-heterosexuals. This suggests that the overall processing of relationships may be more directly linked to sexual orientation than it is directly related to gender. I am not sure what this tells us about the evolutionary role within the species for non-heterosexual behavior, but it raises an interesting question.