Genome Wide Association (GWA) Study for Early Onset Extreme Obesity Supports the Role of Fat Mass and Obesity Associated Gene (FTO) Variants. Even if this is true, these correlations between particular alleles and obesity hold for the modern German lifestyle. I guarantee you that population level diversity in weight correcting for height was sharply attenuated when all Germans were basically farmers and laborers. It seems possible to me that in pre-modern times "obesity alleles" might have been selected for something different in an environment where gaining a lot of weight and becoming subject to higher risk of various chronic diseases was not a plausible outcome. With the change in environment the whole phenotypic landscape shifted as the environment in which the genes expressed was radically altered.
Note: I'm skeptical that obesity alleles mark a much more efficient metabolism. After all, if LCT can nearly fix in northern Europe why not genes which allow you to more efficiently convert food into energy would not have been swept to fixation long ago? I suppose this could be balancing selection, but there's only so much of that a genetic architecture can support.
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This is totaly true. if you look a hundred years ago in fact a fifty yrars ago people are not obece. it's that people have become lazy. you go to work eat like there is no tommoro and go back to work. people use to eat meat and potatos because people use to do a lot of manual labor, we have change the way we work but we didn't change the way we eat. we put the same amount of food in to our body but we did les than half of the manual work. if we change the way we eat and teach out youngsters to eat proper in the near future we would have les chronic diseases and obese people.
"I guarantee you that population level diversity in weight correcting for height was sharply attenuated when all Germans were basically farmers and laborers."
I seem to recall reading a few years ago about a study showing that the Amish had a very low level of heart disease and obesity, despite a high-fat, high-calorie diet. Their lifestyle still involves not much less physical work than that of their German ancestors.
Razib: "why not genes which allow you to more efficiently convert food into energy would not have been swept to fixation long ago?"
Probably because there are big physiological costs. Not obesity or obesity-related syndromes prior to the industrial revolution obviously. Could be any number of things: immune, reproduction, activity. These original costs are difficult to study in a "modern" context in which caloric excess and sedentary activity patterns are the norm. Contemporary humans - whether first or third world - are really bizarre in terms of energetics and hence metabolism, growth, immune, endocrine systems.
Obesity does not only have genetic risk factors but probably is heritable epigenetically, and certainly through prenatal factors (developmental programming), constructed ecological inheritance (trade networks, crops, toxins), and mimetically (which is also laterally transmissible).
Probably because there are big physiological costs. Not obesity or obesity-related syndromes prior to the industrial revolution obviously. Could be any number of things: immune, reproduction, activity.
sure. but are the costs (or benefits) frequency dependent? if the costs exist and outweigh benefits, then it won't rise in frequency. i'm skeptical of balancing selection via overdominance. it could be that the alleles were floating around neutrally in the pre-modern context as well.
of course the theory of natural selection is still in effect. Since most people spends alot of time in the office doing stuffs, then their children would also take a body which more accustomed for officework.
With the change in environment the whole phenotypic landscape shifted as the environment in which the genes expressed was radically altered.
I agree with you. In psychology they argue, is it nature or nurture. Much of the time the answer is yes! It is both! Man is a complex machine but so is the biosphere we live in. They both interact and adapt.
Dave Briggs :~)
it could be that the alleles were floating around neutrally in the pre-modern context as well.
Given the population differences in obesity, that seems less likely. It would be a surprise that, by drift, the pops who've been doing agriculture the longest are the thinnest, while those who've adopted most recently are the fattest.
The photos I have my family (paternal and maternal) from the 1900s to 1950s show very obese women and tall skinny men. The few earlier photos I have show both overweight and skinny for both sexes.
None of these ancestors (including my father and mother) led sedentary indoor job lives. All the work was agricultural in one way or another.
In my childhood, what meat we had was what my father killed and my mother butchered. After I was 10 or so, my father became "rich" by his family's standards, but I was a "chubby" child long before then.
My brother, on the other hand, is skinny as a rail.
So... where do sex differences figure in here?
Since most people spends alot of time in the office doing stuffs, then their children would also take a body which more accustomed for officework.
Exactly! And the giraffe's neck got longer through stretching to reach leaves at the tops of trees!