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Often what looks like an effect of grandparents on kids (controlling for parents) is just genetics -- what you observe in the parents is a noisy measure of some

by iguy 7y ago

Often what looks like an effect of grandparents on kids (controlling for parents) is just genetics -- what you observe in the parents is a noisy measure of some hidden variable, and the grandparents give you additional (noisy) data. > outside a few notable outliers, that there are no "short genes", just environments Predictions based on about 20000 different genes gave correlation 0.65, in the best paper I can find in 5 minutes. (Which was from 2017, a long time in this game.) This is for differences within a European-descended population.

NickNameNick 7y ago
There was a study a while back, based on family records out of scandinavian churches, where they were able to identify patterns in children based on when (or if) their paternal grandfathers had experienced mild famine in a narrow age range. They were further working to tie these effects to a group of epigenetic markers. (possibly successfully, I'm unclear.) It may have been this study: https://en.wikipedia.org/wiki/%C3%96verkalix_study https://en.wikipedia.org/wiki/%C3%96verkalix_study
- AstralStorm 7y ago
  The trouble being that epigenetics effects (if any) are hard to separate from diet and exercise - habits which are also to a big extent heritable in the short run. You'd need to run studies on separated twins to cleanly split the two.
- iguy 7y ago
  I do not know this study, but sentences like "paternal grandfather's food supply was only linked to the mortality RR of grandsons and not granddaughters" in a study with N=303 make me pretty skeptical about p-hacking. There's a lot of academic interest in such things, precisely because they go against the grain of everything that's well understood. Finding one, and proving that it's really certainly not zero, could make your name.
bsanr2 7y ago
>Predictions based on about 20000 different genes gave correlation 0.65, in the best paper I can find in 5 minutes. (Which was from 2017, a long time in this game.) This is for differences within a European-descended population. That's probably the meta-analysis that I was alluding to, which unfortunately gets extrapolated out to humans in general in most discourse. There are two caveats I see. 1) The population described was largely European-descended, and presumably in relatively wealthy, relatively egalitarian environments. Inequality is known to lower a population's average height - not with a general shift downward, but by lowering the floor and increasing the shorter population - so it could be that there is a generally smaller range of heights in that population than in humanity as a whole; and, with environmental variables less variable, the only thing left to determine height is genes. But saying that most of the difference between a 6'2" German and a 6'4" Dane is mostly genetic is very different from saying the same of the difference between a 5'11" African American and a 5'4" El Salvadorian. 2) Even in the population described, it's likely that class mobility is not super high. That means that the relative fortunes of families would not have changed over several generations, even as wealth accrued and the gaps between classes diminished. I'm not a statistician: how likely is it that genes associated with certain families and communities, entrenched in their class as they are, could be flagged as "tall" or "short" genes, respectively, but ultimately have little to do with the physiological processes of growth and development? I realize that those confounding variables are supposed to be controlled for by the analysis, but what if they're so tightly bonded in practice, across a large-enough population, that it's too difficult to separate them until you can actually say what each gene does and how that plays into growth?
- iguy 7y ago
  OK, these are serious questions. 1) This is true, and uncontroversial. Nobody doubts that bonsai are small for environmental reasons. More technically, the heritability of traits is inversely related to how variable the environment is. Once everyone is well-fed & well-cared-for, you expect higher correlations between parents' height and children's, compared to the earlier world where many were stunted. (And likewise you expect a stronger influence of people's innate interests on what jobs they do, once they are rich enough to turn down better-paying alternatives which they hate.) 2) This is a real concern, but it also depends a little bit on what you hope to achieve. My extreme example: If a freak accident on the way home from the 1964 olympics had stranded the Dutch men's & woman's gymnastics teams on the same island as (m&f) Nigerian basketball teams, and you visited today, then in this population genes for blue eyes would be a pretty strong predictor of being short. Because they would mark ancestry, not because of a more direct link. This may not be a terrible thing. If what you want is a test to see who is more susceptible to some illness, for the purpose of giving them screening from age 40 instead of 50, then if what you are detecting is ancestry-markers not heart-muscle-genes, do you care? But for other purposes you may really want to know the functional genes related. One thing you can do is to look only at differences in height (etc) between siblings, who by definition have the same ancestry. This is also done, but it's harder to collect this data, so studies for humans are smaller & noisier. But for plants you can do this very well, control everything. And I think that for dairy cows this is done very well (you know their ancestry perfectly, so the only point of DNA testing is to get information which that doesn't capture).

by iguy 7y ago

NickNameNick 7y ago

There was a study a while back, based on family records out of scandinavian churches, where they were able to identify patterns in children based on when (or if) their paternal grandfathers had experienced mild famine in a narrow age range. They were further working to tie these effects to a group of epigenetic markers. (possibly successfully, I'm unclear.) It may have been this study: https://en.wikipedia.org/wiki/%C3%96verkalix_study https://en.wikipedia.org/wiki/%C3%96verkalix_study

AstralStorm 7y ago
The trouble being that epigenetics effects (if any) are hard to separate from diet and exercise - habits which are also to a big extent heritable in the short run. You'd need to run studies on separated twins to cleanly split the two.
iguy 7y ago
I do not know this study, but sentences like "paternal grandfather's food supply was only linked to the mortality RR of grandsons and not granddaughters" in a study with N=303 make me pretty skeptical about p-hacking. There's a lot of academic interest in such things, precisely because they go against the grain of everything that's well understood. Finding one, and proving that it's really certainly not zero, could make your name.

bsanr2 7y ago

>Predictions based on about 20000 different genes gave correlation 0.65, in the best paper I can find in 5 minutes. (Which was from 2017, a long time in this game.) This is for differences within a European-descended population. That's probably the meta-analysis that I was alluding to, which unfortunately gets extrapolated out to humans in general in most discourse. There are two caveats I see. 1) The population described was largely European-descended, and presumably in relatively wealthy, relatively egalitarian environments. Inequality is known to lower a population's average height - not with a general shift downward, but by lowering the floor and increasing the shorter population - so it could be that there is a generally smaller range of heights in that population than in humanity as a whole; and, with environmental variables less variable, the only thing left to determine height is genes. But saying that most of the difference between a 6'2" German and a 6'4" Dane is mostly genetic is very different from saying the same of the difference between a 5'11" African American and a 5'4" El Salvadorian. 2) Even in the population described, it's likely that class mobility is not super high. That means that the relative fortunes of families would not have changed over several generations, even as wealth accrued and the gaps between classes diminished. I'm not a statistician: how likely is it that genes associated with certain families and communities, entrenched in their class as they are, could be flagged as "tall" or "short" genes, respectively, but ultimately have little to do with the physiological processes of growth and development? I realize that those confounding variables are supposed to be controlled for by the analysis, but what if they're so tightly bonded in practice, across a large-enough population, that it's too difficult to separate them until you can actually say what each gene does and how that plays into growth?

iguy 7y ago
OK, these are serious questions. 1) This is true, and uncontroversial. Nobody doubts that bonsai are small for environmental reasons. More technically, the heritability of traits is inversely related to how variable the environment is. Once everyone is well-fed & well-cared-for, you expect higher correlations between parents' height and children's, compared to the earlier world where many were stunted. (And likewise you expect a stronger influence of people's innate interests on what jobs they do, once they are rich enough to turn down better-paying alternatives which they hate.) 2) This is a real concern, but it also depends a little bit on what you hope to achieve. My extreme example: If a freak accident on the way home from the 1964 olympics had stranded the Dutch men's & woman's gymnastics teams on the same island as (m&f) Nigerian basketball teams, and you visited today, then in this population genes for blue eyes would be a pretty strong predictor of being short. Because they would mark ancestry, not because of a more direct link. This may not be a terrible thing. If what you want is a test to see who is more susceptible to some illness, for the purpose of giving them screening from age 40 instead of 50, then if what you are detecting is ancestry-markers not heart-muscle-genes, do you care? But for other purposes you may really want to know the functional genes related. One thing you can do is to look only at differences in height (etc) between siblings, who by definition have the same ancestry. This is also done, but it's harder to collect this data, so studies for humans are smaller & noisier. But for plants you can do this very well, control everything. And I think that for dairy cows this is done very well (you know their ancestry perfectly, so the only point of DNA testing is to get information which that doesn't capture).