Sexual Differentiation Development Flashcards
sexual dimorphism
any difference, morphological or behavioural, between males and females of the same species
what is the hypothesis regarding the origin of sexual dimorphism
the gonads are differentiated by genetic influences. all other sex differentiation reflects hormonal mediation in utero.
what is the SDN-POA?
a brain structure in the hypothalamus of rats, similar to the human INAH 2 and 3.
Sexually dimorphic nucleus in the preoptic area
it is larger in males than females.
what is the leading theory regarding the cause of male homosexuality?
given female brains are the default, it is believed if the testes develop and release testosterone later, or somehow dont release enough testosterone during a certain period of brain development, then the male will be gay.
unfortunately there is no theory for female homosexuality
is homosexual behaviour seen in other species?
yes :)
how might homosexuality affect the fitness of other species?
it can be a benefit.
male flour beetles, provides male with competitive edge, as when the male he tops goes to mate with a female, he is shooting both males’ sperm. so the top male doesn’t have to mate with the female, but can still impregnate her.
what is the INAH?
a nuclei group in the hypothalamus in humans. similar to the SDN-POA in rats.
Interstitial nucleus of the anterior hypothalamus
INAH 2 and INAH 3.
INAH 3 is larger in males, than females and homosexual men.
what did LeVay hypothesize about the INAH3?
because it is bigger in straight men compared to women and gay men, it is believed that INAH3 is sexually dimorphic (male vs female) and dimorphic in regards to sexual orientation (at least in men)
what did the Byne et al 2001 paper say?
INAH 1-4
INAH 3 is smaller in homosexual than heterosexual men. but number of nuclei are the same.
HIV status greatly influenced volume of INAH 1
what is an issue with the Byne study?
the brains were all taken from cadavers. the sexual orientation of several individuals was presumed, so its not definitive proof if there is a sexual orientation dimorphism.
how can a trait like male homosexuality, which has a genetic component, persist over evolutionary time if the individuals that carry the genes associated with it aren’t reproducing?
indirect fitness.
helping their relatives raise offspring, their genes are being perpetuated in the next generation still, with their help.
hypothesis: genes that code for homosexuality code for other things too!
