5 ms·

X-chromosome inactivation is a type of an epigenetic change. It is one of many that happen throughout the body - I would say there are very few cells in our bod

by tamcap 8y ago

X-chromosome inactivation is a type of an epigenetic change. It is one of many that happen throughout the body - I would say there are very few cells in our bodies that have the same epigenetic markup. We've known about this for a while. The article discusses genetic post-meiotic changes that propagate differentially through the body. We knew it happened for a while now too, but it was always presented as a curiosity or an anomaly. We are now learning that it is much more common than we anticipated. Like presented in the article, it might actually explain some clinical phenotypes as well.

hinkley 8y ago
Don’t organs, limbs, spots and stripes form in a fetus due to epigenetics?
- kyberias 8y ago
  No, they form because of genetics: differential gene regulation.
- rubatuga 8y ago
  You're not wrong, it's a mixture of epigenetic changes, and local environment changes. As a cell differentiates, it definitely changes its epigenome. These changes are also mediated by cell-cell interactions, and other morphogenic proteins, for example, the SHH gene: https://en.wikipedia.org/wiki/Sonic_hedgehog https://en.wikipedia.org/wiki/Sonic_hedgehog
himom 8y ago
Male birth order-linked gayness probability is epigenetics in the mother IIRC.
- gowld 8y ago
  Interesting. https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_sexual_orientation#Empirical_findings https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male... "Secondly, the fraternal birth order effect operates through a biological mechanism during prenatal life, not during childhood or adolescence. Direct evidence for this is the fact that the fraternal birth order effect has been found even in males not raised with their biological brothers – it has been determined that biological brothers increase the odds of homosexuality in later-born males even if they were reared in different households, whereas non-biological siblings, such as step-brothers or adopted brothers, have no effect on male sexual orientation." That is consistency with a "kin-selection" theory of homosexuality, that within a family, evolutionary factors favor having partially non-reproductive members in a family (perhaps because in a family with two males, on average, the total reproductive fitness is greater where there is one father and one uncle, not two fathers)
  - toasterlovin 8y ago
    The math is pretty clear: the chances that homosexuality, as a trait in and of itself, is selected for is highly unlikely. A gay person would have to result in their siblings having 2x as many children as they would have themselves, which is possible, but a really steep hill to climb. The explanation that makes much more sense to me is that homosexuality is an occasional side effect of something else which is highly adaptive to non-gay siblings who possess it.
    - notabee 8y ago
      Humans have many traits that seem to support survival at the tribal level, and having a spectrum of homosexual and heterosexual individuals could well have supported child rearing or reduced divisive competition. Just look at bonobos.
      - toasterlovin 8y ago
        See my reply to rubatuga. If the genetic math doesn't work out for helping raise your sibling's children vs. having children of your own, it absolutely doesn't work for raising the tribe's children (who are less related to you than your sibling's children) vs. having your own.
        notabee 8y ago
        I think you missed my point. If survival of human groups generally occurred at the tribal level, i.e. either a tribe successfully cooperated and survived or suffered excessive discord and died out unless they were adopted by a different tribe, the benefits would not rely just on direct actions within an atomic family unit. The group had to have enough genetic diversity, or invite enough in, to prevent disease from inbreeding but generally most of the tribe would be somewhat related. The "math" surrounding just caring about whoever has 1/2 or 1/4 of one's genetic material may not be as important as the survival of the larger cooperative group. All of those little selfish increments might not matter if isolated, catastrophic group collapse rendered them nil. I think you are trying to over-simplify the scenario. Other traits point to increased cooperation being crucial, such as the idea that concealed ovulation attenuated direct male competition during fertile periods. Even in The Selfish Gene, Dawkins describes game theory situations where certain ratios of populations are stable, like the simplified hawks versus doves. In the same way, there may have been a stable ratio of homosexual tendencies or sexual flexibility that acted as a cooperative buffer, as they would assist in child rearing in the same way that you mention grandmothers. Trying to boil it down to just grandmothers because they might have the largest genetic "interest" is overly reductionist. It's not just an addition problem. And bonobos are a great example of all with all sexual bonding being very close to us genetically. Who's to say that our cultural notions of what homosexuality entails translates across to thousands of years of pre-historical culture?

by tamcap 8y ago

hinkley 8y ago

Don’t organs, limbs, spots and stripes form in a fetus due to epigenetics?

kyberias 8y ago
No, they form because of genetics: differential gene regulation.
rubatuga 8y ago
You're not wrong, it's a mixture of epigenetic changes, and local environment changes. As a cell differentiates, it definitely changes its epigenome. These changes are also mediated by cell-cell interactions, and other morphogenic proteins, for example, the SHH gene: https://en.wikipedia.org/wiki/Sonic_hedgehog https://en.wikipedia.org/wiki/Sonic_hedgehog

himom 8y ago

Male birth order-linked gayness probability is epigenetics in the mother IIRC.

gowld 8y ago
Interesting. https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male_sexual_orientation#Empirical_findings https://en.wikipedia.org/wiki/Fraternal_birth_order_and_male... "Secondly, the fraternal birth order effect operates through a biological mechanism during prenatal life, not during childhood or adolescence. Direct evidence for this is the fact that the fraternal birth order effect has been found even in males not raised with their biological brothers – it has been determined that biological brothers increase the odds of homosexuality in later-born males even if they were reared in different households, whereas non-biological siblings, such as step-brothers or adopted brothers, have no effect on male sexual orientation." That is consistency with a "kin-selection" theory of homosexuality, that within a family, evolutionary factors favor having partially non-reproductive members in a family (perhaps because in a family with two males, on average, the total reproductive fitness is greater where there is one father and one uncle, not two fathers)
- toasterlovin 8y ago
  The math is pretty clear: the chances that homosexuality, as a trait in and of itself, is selected for is highly unlikely. A gay person would have to result in their siblings having 2x as many children as they would have themselves, which is possible, but a really steep hill to climb. The explanation that makes much more sense to me is that homosexuality is an occasional side effect of something else which is highly adaptive to non-gay siblings who possess it.
  - notabee 8y ago
    Humans have many traits that seem to support survival at the tribal level, and having a spectrum of homosexual and heterosexual individuals could well have supported child rearing or reduced divisive competition. Just look at bonobos.
    - toasterlovin 8y ago
      See my reply to rubatuga. If the genetic math doesn't work out for helping raise your sibling's children vs. having children of your own, it absolutely doesn't work for raising the tribe's children (who are less related to you than your sibling's children) vs. having your own.
      - notabee 8y ago
        I think you missed my point. If survival of human groups generally occurred at the tribal level, i.e. either a tribe successfully cooperated and survived or suffered excessive discord and died out unless they were adopted by a different tribe, the benefits would not rely just on direct actions within an atomic family unit. The group had to have enough genetic diversity, or invite enough in, to prevent disease from inbreeding but generally most of the tribe would be somewhat related. The "math" surrounding just caring about whoever has 1/2 or 1/4 of one's genetic material may not be as important as the survival of the larger cooperative group. All of those little selfish increments might not matter if isolated, catastrophic group collapse rendered them nil. I think you are trying to over-simplify the scenario. Other traits point to increased cooperation being crucial, such as the idea that concealed ovulation attenuated direct male competition during fertile periods. Even in The Selfish Gene, Dawkins describes game theory situations where certain ratios of populations are stable, like the simplified hawks versus doves. In the same way, there may have been a stable ratio of homosexual tendencies or sexual flexibility that acted as a cooperative buffer, as they would assist in child rearing in the same way that you mention grandmothers. Trying to boil it down to just grandmothers because they might have the largest genetic "interest" is overly reductionist. It's not just an addition problem. And bonobos are a great example of all with all sexual bonding being very close to us genetically. Who's to say that our cultural notions of what homosexuality entails translates across to thousands of years of pre-historical culture?