7 ms·

I'd definitely be surprised if a significant portion of homosexuality wasn't environmental, but to my knowledge there is a degree of heritability shown in twin

I'd definitely be surprised if a significant portion of homosexuality wasn't environmental, but to my knowledge there is a degree of heritability shown in twin studies. Actually reading the article shows that they found several genes that each contribute, but no single gene. That shouldn't be surprising to anyone, considering that almost every complex trait is somewhat affected by a huge number of genes each tweaking the result by a small amount. Remember that DNA controls the development of the body through an insanely complicated Rube Goldberg machine, no one should expect a 1:1 correspondence between any complicated trait and a gene.

anaphor 6y ago
Remember that heritability is a measure of a population, not an individual. So you're measuring the amount that genes vs environment contributes to a trait within that population. It's not an absolute number.
- ravi-delia 6y ago
  I mean, yeah? It's still fairly strong evidence against there being literally no genetic component to homosexuality, which I definitely saw a lot of in this thread. Unless I misunderstand your comment?
  - anaphor 6y ago
    Not disagreeing with your original point, just adding that if you were controlling for environmental factors (everyone has equivalent environment), then you'd see more contribution to variance in phenotypes from genetics than environment. So for homosexuality, I'd bet the reason genetics don't contribute as much is because of the heterogeneous environmental conditions (just think about where you grow up and what religion you are for example). Edit: a good example of this in action is handedness, because different societies historically have different advantages to using different hands > Second, the samples used to estimate the handedness heritability were from different places, different years or different centuries and were not always representative of the general population. Heritability is not an intrinsic property of a trait: it varies with phenotypic and additive genetic variances and thus can vary across populations and across generations https://www.nature.com/articles/s41437-019-0274-3 https://www.nature.com/articles/s41437-019-0274-3
    - ravi-delia 6y ago
      Ahh got it, thanks for clarifying. That definitely makes sense, and clicks with my intuition that genetics and the environment are sort of both 100% responsible.
hajile 6y ago
Identical twin studies point away from genetics very hard. Pretty much all genetic anomalies will affect both identical twins 100% of the time. The fact that it's less than 40% points much more to environmental effects rather than genes.
- mr_overalls 6y ago
  A concordance rate of 40% actually points to a near-even split between heritable and non-heritable factors.
- drocer88 6y ago
  From the link: "Research from the 1990s2 showed that identical twins are more likely to share a sexual orientation than are fraternal twins or adopted siblings." Study here : https://pubmed.ncbi.nlm.nih.gov/9549243/ https://pubmed.ncbi.nlm.nih.gov/9549243/ "We present an overview of behavioral genetics research on homosexual and heterosexual orientation. Family, twin, and adoptee studies indicate that homosexuality and thus heterosexuality run in families. "
  - jdgoesmarching 6y ago
    This thread seems very insistent on pushing the environmental case when presented with evidence to the contrary. It’s like I stumbled into a Republican convention in the 90s. Baseless theories: people do this to feel better about LGBT discrimination or the idea of sexuality being out of our control is too scary for dudes who haven’t come to terms with their own masculinity. The latter isn’t necessarily shade, I’m not sure I figured it out until my mid-20s.
    - coldtea 6y ago
      Hello, 1990 called. It's 2021, gender (including sexuality) is fluid. And yet, it's the other commenters who seem backwards to you?
      - ravi-delia 6y ago
unishark 6y ago
The same goes for a cause we'd consider purely environmental, such as an illness caused by an infection. There will still be lots of associated genes with small effect determining how resilient a person is to the infection. Twins share environmental causes from early stages of development (like an infection during pregnancy) so that angle gets potentially confounded too.
- ravi-delia 6y ago
  Twin studies typically compare identical and fraternal twins to eliminate such environmental factors (Obviously there are still errors, but they generally wind up as counting towards environmental). And of course polygenetic factors probably have a sort of necessary-but-not-sufficient type of relationship with the traits they contribute too, but that doesn't mean that anything that isn't pegged to a single gene can be thought of as environmental.
kabirgoel 6y ago
Tangential to your point, but I enjoy the comparison you draw between DNA mechanisms and Rube Goldberg machines. It’s an apt metaphor because DNA, and the body as a whole, is constructed quite randomly according to the demands of the environment.
- ravi-delia 6y ago
  Oh absolutely! I can remember being so confused for so long about how DNA could possibly code for everything in an animal until I learned how convoluted and indirect the effect is. So much of what genes do is totally mediated by the process of development, emergent interactions between cells. No wonder we so rarely find clean correspondences between genes and traits, its honestly a miracle even polygenetic statistics find anything.

anaphor 6y ago

Remember that heritability is a measure of a population, not an individual. So you're measuring the amount that genes vs environment contributes to a trait within that population. It's not an absolute number.

ravi-delia 6y ago
I mean, yeah? It's still fairly strong evidence against there being literally no genetic component to homosexuality, which I definitely saw a lot of in this thread. Unless I misunderstand your comment?
- anaphor 6y ago
  Not disagreeing with your original point, just adding that if you were controlling for environmental factors (everyone has equivalent environment), then you'd see more contribution to variance in phenotypes from genetics than environment. So for homosexuality, I'd bet the reason genetics don't contribute as much is because of the heterogeneous environmental conditions (just think about where you grow up and what religion you are for example). Edit: a good example of this in action is handedness, because different societies historically have different advantages to using different hands > Second, the samples used to estimate the handedness heritability were from different places, different years or different centuries and were not always representative of the general population. Heritability is not an intrinsic property of a trait: it varies with phenotypic and additive genetic variances and thus can vary across populations and across generations https://www.nature.com/articles/s41437-019-0274-3 https://www.nature.com/articles/s41437-019-0274-3
  - ravi-delia 6y ago
    Ahh got it, thanks for clarifying. That definitely makes sense, and clicks with my intuition that genetics and the environment are sort of both 100% responsible.

hajile 6y ago

Identical twin studies point away from genetics very hard. Pretty much all genetic anomalies will affect both identical twins 100% of the time. The fact that it's less than 40% points much more to environmental effects rather than genes.

mr_overalls 6y ago
A concordance rate of 40% actually points to a near-even split between heritable and non-heritable factors.
drocer88 6y ago
From the link: "Research from the 1990s2 showed that identical twins are more likely to share a sexual orientation than are fraternal twins or adopted siblings." Study here : https://pubmed.ncbi.nlm.nih.gov/9549243/ https://pubmed.ncbi.nlm.nih.gov/9549243/ "We present an overview of behavioral genetics research on homosexual and heterosexual orientation. Family, twin, and adoptee studies indicate that homosexuality and thus heterosexuality run in families. "
- jdgoesmarching 6y ago
  This thread seems very insistent on pushing the environmental case when presented with evidence to the contrary. It’s like I stumbled into a Republican convention in the 90s. Baseless theories: people do this to feel better about LGBT discrimination or the idea of sexuality being out of our control is too scary for dudes who haven’t come to terms with their own masculinity. The latter isn’t necessarily shade, I’m not sure I figured it out until my mid-20s.
  - coldtea 6y ago
    Hello, 1990 called. It's 2021, gender (including sexuality) is fluid. And yet, it's the other commenters who seem backwards to you?
    - ravi-delia 6y ago

unishark 6y ago

The same goes for a cause we'd consider purely environmental, such as an illness caused by an infection. There will still be lots of associated genes with small effect determining how resilient a person is to the infection. Twins share environmental causes from early stages of development (like an infection during pregnancy) so that angle gets potentially confounded too.

ravi-delia 6y ago
Twin studies typically compare identical and fraternal twins to eliminate such environmental factors (Obviously there are still errors, but they generally wind up as counting towards environmental). And of course polygenetic factors probably have a sort of necessary-but-not-sufficient type of relationship with the traits they contribute too, but that doesn't mean that anything that isn't pegged to a single gene can be thought of as environmental.

kabirgoel 6y ago

Tangential to your point, but I enjoy the comparison you draw between DNA mechanisms and Rube Goldberg machines. It’s an apt metaphor because DNA, and the body as a whole, is constructed quite randomly according to the demands of the environment.

ravi-delia 6y ago
Oh absolutely! I can remember being so confused for so long about how DNA could possibly code for everything in an animal until I learned how convoluted and indirect the effect is. So much of what genes do is totally mediated by the process of development, emergent interactions between cells. No wonder we so rarely find clean correspondences between genes and traits, its honestly a miracle even polygenetic statistics find anything.