4 ms·

IANAS, but from what I understand, it's more complicated than that. A parent's or grandparent's childhood health has been shown to affect the growth and health

by bsanr2 7y ago

IANAS, but from what I understand, it's more complicated than that. A parent's or grandparent's childhood health has been shown to affect the growth and health of their descendents. These effects only go away after several generations of adequate nutrition and health. Tall women tend to give birth to larger babies not (directly) because of a "tall gene", but because of the physiological realities of their bodies (i.e., more space). We've recently identified several traits that are hereditary and that can stunt growth, but that had previously not been linked directly to a given family's shortness (e.g., sleep apnea and gluten sensitivity), and which have interventions much less radical than genetic modification. It seems clear-cut, and there are studies that link certain genes to height on a statistical level. But I suspect we're going to find that height has little to do with genetics in the traditional sense, and outside a few notable outliers, that there are no "short genes", just environments that fit specific genetic profiles that are or are not available to the people with those genes. Europeans are tallest in a generalized global monoculture where Western diets and lifestyles are the norm, and where European-descended populations have enjoyed a generally higher quality of life for several generations. Color me surprised.

brudgers 7y ago
On average having healthy parents and grandparents seems more likely to create environments where a child’s wellbeing can be a focus of attention. Or more crudely, a dead grandparent can’t teach a child banjo or help with fractions or pay for glasses.
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?

by bsanr2 7y ago

brudgers 7y ago

On average having healthy parents and grandparents seems more likely to create environments where a child’s wellbeing can be a focus of attention. Or more crudely, a dead grandparent can’t teach a child banjo or help with fractions or pay for glasses.

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?