Human Size

[Guest vix]

Why did the size of humans change over time, especially with people in East Asia? I've always thought that the further you head from Africa, the shorter people you can find.

 

I've just been curious as to why most in East Asia are just lots smaller than most everyone else. Was there something favored by people that were short in that part of the world way back then?

 

Thanks

[Sorcerer]

Nothing favoured nothing gained, it seems that height had no selective advantage in east asia, combined with malnutrition and lack of hybrid vigor this will lead to a population whos height isn't selected for. In other populations (europe) height was a factor in sexual selection, with taller males being more desirable, and also asia minor was a source of influx of new genes giving hybrid vigor.

 

In east asia height wasn't a sexual selection trait because women were culturally submissive to men and therefore had very little say in mate selection, although they were submissive to men in europe, it was to a lesser extent.

 

I am not sure how much of this post is true, I would back it up with papers if I could be fux, but I am drunk and have low motivation because I also smoke pot (apparently).

[Guest vix]

In east asia height wasn't a sexual selection trait because women were culturally submissive to men and therefore had very little say in mate selection' date=' although they were submissive to men in europe, it was to a lesser extent.

[/quote']

 

I had considered that, but is there really a connection between size and submission? There probably was something about size that men choose, but I have a feeling theres at least a little bit more to it.

 

Thanks for the input.

[Dak]

dispite the fact that he was drunk/stoned, he actually had a very good point.

 

a common and forgivable misinterpretation of one of the central tennets of natural evolution is that traits get passed on based on their fitness to survive; ie, that the more a trait increases an organisms ability to survive long enough to reproduce, the higher the frequency with which it is passed on.

 

in actual fact, the statement should read "the ability of a trait to get passed on is based on its ability to get the posesser of the trait laid" (you wont find it worded like that in a text book, but its pretty accurate anyway).

 

so, traits that increase an organisms ability to survive to an age where they can reproduce will get passed on. the difference between the second statement and the first is that it highlites the fact that traits that make an organism more sexually appealing also get passed on, even if the trait confers no extra benifits and does not increase the ability of the organism posessing it to survive.

 

so, if small size is considered attractive in east asia (because femail submissivness is concidered attractive), then this would be enough to promote the inheritance of 'smallness', and thus drive evolution to making east asians smaller/preventing them from getting larger

[coquina]

Amongst other things, they have original Colonial "lasts" (wooden molds) from which adults shoes were made. The average size is quite small. Also, when you go aboard the replicas of the Susan Constant, Godspeed, and Discovery, there is no headroom for an average sized modern person. The interpreters said that most men were shorter than 5'6".

 

Apparently, good nutrition and improved medical care over the last 400 years has led to people becoming taller on average. I'm not saying this is due to evolution, but due to the fact that people did not previously attain maximum growth due to malnutrition.

[Xavier]

Gross cultural stereotyping of sexual mores is unlikely to explain any evolutionary consequences as they are too short term in evolutionary timescales and often just plain wrong.

 

Consider elephant seals, for an example where a bull has a harem of up to 100 cows from whom he keeps away all other males. The females have no choice and are entirely submissive - but the 1-2% of bulls that manage to acquire a harem are aggressively selected for prowess. The females (or their genes) have chosen to accept this system.

 

In the case of submissiveness the removal of sexual selection behaviour would be unlikely to occur because that would cause a big loss in inclusive fitness (which includes the sum of the ability to survive, mate, reproduce, rear the young and anything else that increases the chance of your genes being numerous in succeeding generations)

(This presumes that the capacity for sexual selection ie. brainpower, senses and something upon which to judge the other gender are available to the organism)

 

It is very easy to become Adaptationist and conclude that if there is an observed difference in populations of a species there must be different evolutionary pressures the populations due to their different environments. An alternative is hybrid vigour; or the "make me taller" genetic variant may have fallen into disuse in the past and by chance been lost completely from one population and not the other so when the environment changes for both populations making tallness desirable, in one group the pre-existing gene increases in number whilst the other group must wait for a novel mutation to turn up by chance.

 

But there is plenty of variation in height between individuals suggesting that varients are available and that there are many contributary causes for the effect of adult body length (ie. size of your mothers womb, your fathers ability to procure good proteinaceous food) so I prefer the idea that there is some environmental difference between the oriental and occidental hemispheres.

The effect could be nurture, not nature - as Coquina said nutrition is usually credited with the national growth spurts of recent history. The average heights of victorian schoolchildren from wealthy public schools were as much as six inches greater than their peers in the first schools for the poor (and there is still a measurable difference today) and the increase in average height appears to take a generation or two to become established after the diet is improved (not due to genetic changes, of course, but perhaps a mother who is undernourished as a child when the body's insulin tolerance and body fat (leptin) levels are 'calibrated' will still produce a small child even if she is well nourished as her body is still 'programmed' to expect lean times and not to lavish more than minimal nutrients on the baby) so perhaps asia is still 'catching up' with our level of excess and engorgement.

 

Surface area to volume ratio decreases as size increases, making a large body easier to keep warm in a cold climate. This suggests why europeans are taller than asians. Alternatively, they may have been the prey of different styles of predator; the burst-speed predator such as a tiger in asia could be evaded with stealth, speed or agility requiring a small stature whilst the european top predator, the wolf was an endurance hunter and the only way to evade was to out-endurance or out-fight (ie. outnumber) it which demanded bulk.

Perhaps the food supply in asia was so consistently good that lean times were rare but elsewhere the food supply was intermittent and it was necessary to gorge in times of plenty and a large mass helped pile on the fat and eke out the reserves in time of famine. This behaviour is consistent with the greater tendency towards obesity from east to west.

[Dak]

when humans first entered west europe, we were quite unsuited to life here -- different predetors, different climate, different food availability etc.

 

as xavior pointed out, these can cause a need to increase in size (heat retention, ability to store food in fat etc)

 

if resorses were low, then this would also give a benifit to humans who were bigger, as they could take resorses off of the smaller humans, which would also drive the evolution of humans becoming larger.

 

as east asia is closer in climate and conditions to africa (where humans come from), maybe humans had less of a difficult time surviving so their was less need for humans to fight amongst themselfs for resorses and so less pressure to increase in size

[ku]

It may be likely that environmental factors play a larger than expected role in Asian height. Consider the increase in the living standards of the Japanese and their increase in average height.