The Amish make an interesting testbed for nature-nurture studies, since the plain people so radically social engineer their environments to equalize them. The Amish are like 18th Century SJWs who, rather than just complain like 21st Century ones, actually built a sustainable culture that minimizes inequality. When progressives say things like, “All we have to do is create a culture that minimizes inequality,” well, the Amish more or less did that. (The Amish are like the Mormons, who do an impressive job of reproducing 1950s American mass middle class prosperity, on steroids and CRISPR.)
One of the late anthropologist Henry Harpending’s later theories (with Greg Cochran) before his recent death was that the Amish over their 10 generations in America have been evolving toward being more naturally Amish-acting. (The Amish have little in the way of gene flow in from the outside because they don’t pursue converts, and they let their teens who find the plain lifestyle personally intolerable leave.)
A major problem facing medical studies, whether of genes or diets or whatever, is self-selection messing with our understanding of the arrow of causality. For example, if people who have a certain genetic mutation live ten years longer, is it the gene variant, or is it because the gene encourages them to choose for themselves a certain lifestyle? Or because a certain lifestyle is statistically correlated with a certain gene for coincidental reasons?
But studies of gene variants among Amish populations suffer less severely from those problems of deducing causation from statistical correlation. The Amish don’t allow much in the way of self-selection of one’s lifestyle, however, so nature-nurture conundrums are slightly less complicated in the case of studies of the Amish.
This is another version of the general conundrum in nature-nurture related studies that as the environment becomes more equal, genes become more important. The heritability of height, for example, used to be only moderate due to poor environments, such as malnutrition, keeping individuals from reaching their genetic potential for height. But, since most forms of height-reducing inequality have been greatly diminished, height is now much more heritable (a.k.a., genetically determined) than only a few generations ago.
From the NYT:
Amish Mutation Protects Against Diabetes and May Extend Life
By ANAHAD O’CONNOR NOV. 15, 2017
Amish carriers of the mutation live on average to age 85, about 10 years longer than their peers. Among the Amish who did not have the mutation, the rate of Type 2 diabetes was 7 percent. But for carriers of the mutation, the rate was zero, despite leading the same lifestyle and consuming similar diets. Tests showed that carriers of the mutation had 28 percent lower levels of insulin, a hormone whose chronic elevation can lead to Type 2 diabetes.
The article suggests the sample size was only 177, so I’m not sure how trustworthy these results are.
… Amish men and women who inherit two copies of the PAI mutation, one from each parent, for example, produce no PAI-1 at all and develop a bleeding disorder similar to hemophilia. So-called carriers who inherit just one copy of the mutation, however, produce less PAI-1 than the average person but still have enough of it to avoid any obvious clotting disorders or other downsides.
So, this mutation is like the sickle cell mutation that evolved in Africa as a desperate stopgap against falciparum malaria: inheriting one copy of the mutant gene gives you a better chance of surviving the most dangerous form of malaria, but two copies kills you young (without modern medical intervention).
The researchers of this Amish mutation are hoping to come up with a pill you could take that would mimic in effect the one allele version.
This appears to be related to the tendency of modern civilized humans to have blood that clots too easily for our easy lifestyles. Our ancestors evolved hunting large, dangerous beasts and then wielding dangerous farm tools. They presumably got wounded all the time, and therefore they needed blood that clotted fast. But we don’t need quite as much clotting ability anymore. (Of course, we’d need some or we’d be hemophiliacs, which is not good.)