Lactose tolerance a key to evolution?

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Mefiante (May 26, 2011, 10:44:38 AM):
Reverting to the diet of that era would not result in Europeans, within one or a few generations, "shrinking" to that size again.
Yes, it would, and within a single generation, too, provided the diet (and lifestyle) reversion is complete and comprehensive in the society under scrutiny. You don’t even need to go back to Roman times. Just 500 years is enough to make the point. As mentioned before, the reverse effect was strikingly illustrated by the Japanese in particular, pretty much over a single generation, where post-war Japanese grew much taller, having been raised during and after the reconstruction years when Japan moved from being an agrarian feudal society to a modern industrial giant. Even today, primitive hunter-gatherer peoples tend to be appreciably shorter than modern societies. For tallness to be a direct evolutionary effect (i.e. directly attributable to genes) there must be a selective advantage, survival and/or reproductive, to being tall that will push the population mean tallness to increasing values over successive generations. While there may indeed be a lesser element of sexual selection to this in modern humans, it’s hardly obvious what that advantage might be, and a significant genetic shift in such a species trait over just a few tens of generations will only be achieved if there is also a commensurately severe selection pressure that drives it. Tallness simply doesn’t fit that profile.

'Luthon64
Rigil Kent (May 26, 2011, 11:29:56 AM):
Each person must be born with the potentiality for both minimum and maximum height. He will reach the latter only under perfect dietary conditions, and the former only under dietary conditions that barely keep him alive.

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Reverting to the diet of that era would not result in Europeans, within one or a few generations, "shrinking" to that size again.

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Yes, it would,


So the claim is that the minimum potential height of humans remained constant in the last few thousand years, correct?

Mintaka
Mefiante (May 26, 2011, 12:32:11 PM):
So the claim is that the minimum potential height of humans remained constant in the last few thousand years, correct?
No, the claim is that the explanation for the observed increase in average human height is not primarily evolution. As said, the combination of slight selective pressure together with the few tens of generations available for genetic fixing is not sufficient to explain adequately the observed increase. It is much more plausibly explained by improvements in people’s living conditions. Japan apart, in Europe, the last 150 years (about six generations) saw an average increase in people’s height of around 14 cm, or ±8%, which is a sizeable change. Moreover, even in relatively homogeneous modern societies, tallness is correlated with socioeconomic status such that wealthier people also tend to be taller, and this difference was much more pronounced just a century ago. That just ain’t evolution. You can read more about the subject here and here.

'Luthon64
Hermes (May 26, 2011, 12:38:12 PM):
Reverting to the diet of that era would not result in Europeans, within one or a few generations, "shrinking" to that size again.
Good point. I suspect the observed increase in (potential maximum) height is at least partly due to sexual selection.
Mintaka
Yes, the taller person may indeed be higher up in the pecking order. This contradicts the Framingham study cited by beLIEf in the OP:
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"What we have found with height and weight basically is that natural selection appears to be operating to reduce the height and to slightly increase their weight."
Hermes (May 26, 2011, 13:16:00 PM):
Reverting to the diet of that era would not result in Europeans, within one or a few generations, "shrinking" to that size again.
Yes, it would, and within a single generation, too, provided the diet (and lifestyle) reversion is complete and comprehensive in the society under scrutiny. You don’t even need to go back to Roman times. Just 500 years is enough to make the point. As mentioned before, the reverse effect was strikingly illustrated by the Japanese in particular, pretty much over a single generation, where post-war Japanese grew much taller, having been raised during and after the reconstruction years when Japan moved from being an agrarian feudal society to a modern industrial giant. Even today, primitive hunter-gatherer peoples tend to be appreciably shorter than modern societies. For tallness to be a direct evolutionary effect (i.e. directly attributable to genes) there must be a selective advantage, survival and/or reproductive, to being tall that will push the population mean tallness to increasing values over successive generations. While there may indeed be a lesser element of sexual selection to this in modern humans, it’s hardly obvious what that advantage might be, and a significant genetic shift in such a species trait over just a few tens of generations will only be achieved if there is also a commensurately severe selection pressure that drives it. Tallness simply doesn’t fit that profile.

'Luthon64
We are in agreement that the selection driver is more obvious in the case of lactose tolerance, but a sexual preference for taller people cannot be excluded as a possible influence. The main point I originally made was that claims in the Farmingham study that shorter and fatter people have more children and that that is prove of evolution at work is rather suspect. This would be even more so if evolution played no role in changing tallness.

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