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Lactose tolerance a key to evolution?

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Mefiante
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« Reply #15 on: 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.

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Rigil Kent
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« Reply #16 on: 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.

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

Quote
Yes, it would,


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

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Mefiante
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« Reply #17 on: 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.

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« Reply #18 on: 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."
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Hermes
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« Reply #19 on: 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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Mefiante
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« Reply #20 on: May 26, 2011, 14:05:18 PM »

… a sexual preference for taller people cannot be excluded as a possible influence.
Indeed, and such a mechanism was proposed as possibly ancillary, not ruled out.

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.
Okay, but I understood your question (“Have humans not been getting taller?”) to mean that you were suggesting the evolutionary trend was actually opposite to that reported in the Framingham study.  The linked-to article in the OP does indicate that the study was controlled for nutritional factors.  It may thus be that in reality tallness/slenderness is in modern times being genetically more fully expressed due to improved living conditions, but that is also being selected against, rather than shortness/plumpness being selected for.  The important question to ask is what factor(s) may be propelling the selection because the background genetic material was drawn from essentially the same population.  As such, the variations therein would be within statistical expectation.

This would be even more so if evolution played no role in changing tallness.
Sure, but it wasn’t asserted that evolution, or genetics for that matter, plays no role.

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Hermes
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« Reply #21 on: May 26, 2011, 15:14:55 PM »

It could be argued that fashion plays a role in the selection of a sex partner.  If tall, slim partners are in vogue, there would be social status associated with partnering with such a person.  Such social status might overrule more hereditary preferences in partner selection.  Considering that fashions change and can be quite whimsical, the distinction between natural and artificial selection becomes blurred in such a situation.
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Majin
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« Reply #22 on: May 26, 2011, 15:37:26 PM »

The health of the parents and the food the parents consume, before and during the pregnancy determines how healthy you are later in life. Wouldn't the food they eat determine aswell how much weight you carry during your life time? If you were to imagine a mother not having enough food to eat, wouldn't the child be underdeveloped. And then also a child being born premature has a effect to.

So I think there is various factors that can determine this, both internal and external.
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« Reply #23 on: May 27, 2011, 16:27:17 PM »

Tallness is not genetically fixed in the same way that lactose tolerance is.

Maybe lactose tolerance and tallness are linked - it is very difficult to find dairy products being sold in countries such as China and Thailand and indigenous people of these countries are noticeably more vertically challenged.(Apart from Bao Xishun one of  the tallest men in the world) Of course many people now also include Western junk food in their diets, but on the whole it has been the same for generations. Short breeding short.
 Just an observation on my travels.
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Hermes
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« Reply #24 on: May 27, 2011, 19:31:56 PM »

Tallness is not genetically fixed in the same way that lactose tolerance is.
Maybe lactose tolerance and tallness are linked - it is very difficult to find dairy products being sold in countries such as China and Thailand and indigenous people of these countries are noticeably more vertically challenged.(Apart from Bao Xishun one of  the tallest men in the world) Of course many people now also include Western junk food in their diets, but on the whole it has been the same for generations. Short breeding short.
 Just an observation on my travels.
And what a challenging observation, beLIEf! (+1)
Now figure this out: If lactose tolerance is driven by natural selection and tallness is linked to lactose tolerance, would that (necessarily) imply that tallness is driven by natural selection?
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beLIEf
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« Reply #25 on: May 27, 2011, 20:10:40 PM »

In that case Hermes, then yes I believe it would. Perhaps a combination of natural selection and slight mutation since lactose intolerance still exists in individuals in otherwise lactose tolerant nations. I think people are significantly more likely to choose their partners based on their height rather than their love of dairy products - but then the tall ones might only be tall because of their ability to digest moo juice.... a conundrum indeed. Which came first tall people or dairy farming?  Huh?
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Mefiante
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« Reply #26 on: May 27, 2011, 22:10:06 PM »

Maybe lactose tolerance and tallness are linked - it is very difficult to find dairy products being sold in countries such as China and Thailand and indigenous people of these countries are noticeably more vertically challenged.
Most southern African indigenous ethnic groups have been nomadic cattle herders for several centuries, living off dairy in addition to beef.  Their lactose tolerance is hardly in question.  Yet, they are on average short and slight peoples by European/US standards with the Kenyan/Tanzanian Maasai being one exception in the tallness department.  This seems to run counter to any simple link between lactose tolerance and tallness.



Short breeding short.
Of course there’s a strong genetic component in this.  It applies within ethnic groups as much as between them, but the question is how increasing tallness in recent human history is best explained: evolution or improved living standards?

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Hermes
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« Reply #27 on: May 28, 2011, 02:44:03 AM »

Oh come all ye newbies!
lurking in your hundreds,
come forth, freck apostrophobia
and say your say!

This is your forum as well!
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beLIEf
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« Reply #28 on: May 28, 2011, 10:11:08 AM »

Oh come all ye newbies!
lurking in your hundreds,
come forth, freck apostrophobia
and say your say!

This is your forum as well!



Does that mean all you hero members have apostrophilia??

Maybe lactose tolerance and tallness are linked - it is very difficult to find dairy products being sold in countries such as China and Thailand and indigenous people of these countries are noticeably more vertically challenged.
Most southern African indigenous ethnic groups have been nomadic cattle herders for several centuries, living off dairy in addition to beef.  Their lactose tolerance is hardly in question.  Yet, they are on average short and slight peoples by European/US standards with the Kenyan/Tanzanian Maasai being one exception in the tallness department.  This seems to run counter to any simple link between lactose tolerance and tallness.

Short breeding short.
Of course there’s a strong genetic component in this.  It applies within ethnic groups as much as between them, but the question is how increasing tallness in recent human history is best explained: evolution or improved living standards?

'Luthon64

I wasn't implying the link was simple, just interestingly observable and of course nutritionally speaking would linked to a myriad of factors other than lactose. I think tallness is rather a result of both evolution and improved living standards, maybe the thing that needs clarification and is more difficult to determine is which factor has had the greatest influence.



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Hermes
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« Reply #29 on: May 28, 2011, 11:54:03 AM »

I wasn't implying the link was simple, just interestingly observable and of course nutritionally speaking would linked to a myriad of factors other than lactose. I think tallness is rather a result of both evolution and improved living standards, maybe the thing that needs clarification and is more difficult to determine is which factor has had the greatest influence.
One could also look at it from the opposite side and argue that in situations where food is scarce, such as among the hunter-gatherers, there is a competitive advantage to being small and able to survive on less food.
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