Submitted by dxrknxrth t3_ztc5yv in askscience
So, genetically and evolutionarily speaking, are people who live in colder countries better at staying warm and less susceptible to the effects of cold weather, such as frostbite?
And similarly, are people who live in warmer climates less susceptible to effects of warm weather, such as sunburn or skin cancer?
Among other things the basal metabolic rate of someone who's been exposed to the cold regularly for a while rises, and they tend to put on additional brown fat which produces heat. It might be interesting to see if the response is stronger in populations that have existed in cold places for s long time vs say, a population that lives near the equator. I suspect that there isn't enough time to evolve huge change in the capacity to alter the strength of this response though and people are actually really good at causing gene flow through all their different subpopulations even in antiquity.
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As the two others have said, absolutely. We have severa morphological features that are different between populations of different climates.
2- limb proportions and crania shape follow similar trends to those above. These really refer to Allen’s rule and Bregman’s rules.
3- body hair distribution is larger in colder climates compared to populations in hot climates.
4- skin melanin content- in hot climates with greater radiation from the sun, the skin is more melanated than those climates with less solar radiation. Melanin is protective against solar UV radiation, but prohibitive of melanin production in the absence of sunlight.
5- nasal complex shape- there are climate associations, though the functional explanation has yet to be fully understood. The general thinking goes colder populations tend to have taller narrower nasal airways to promote heat transfer from the nasal mucosa to the cold inspired air to prevent injury to the lungs. This pressure is of no concern in warmer climates so the shapes is short and broad to maximize airflow or inspiratory and expiratory volume during breathing.
Anyhow, yes there are evolutionary adaptations in human populations to cope with the climate they and their ancestors descended from.
> Body shape
Due to the impact of nutrition it's tough to get a good data set for this. However, the tallest people in the world are generally Northern Europeans or those descended primarily from Northern Europe (cold weather climates). The shortest people in the world are from warm climates in South and Southeast Asia. Africans are about in the middle.
> body hair distribution is larger in colder climates compared to populations in hot climates.
Body hair on human beings does not play any meaningful role in temperature regulation so there wouldn't be any evolutionary pressure. I don't care how glorious your chest hair is, you're not walking across the Northwest Territories naked in winter.
This also doesn't pass even the most cursory examination. Amongst Caucasians, the hairiest tend to be Mediterranean and Semitic peoples from temperate climates while the least hairy tend to be Northern Europeans from cold ones. Indians (from the scorching sub-continent) are notoriously hairy while Koreans (from the freezing Korean Peninsula) are amongst the least hairy people on the planet.
> skin melanin content
This is a common explanation, but the same sort of mechanism/evidence problems emerge.
UV protection does not seem to have any meaningful purpose here. Diseases such as melanoma that strike people with pale skin more often do not generally emerge until well after childbearing years. Sunburns, while unpleasant, can be easily avoided through the use of clothing and shelter. Moreover, it's fairly easy to get a sunburn even in deep winter if you spend a great deal of time outdoors without any protection.
Vitamin D is more likely to be the culprit. However, the main input to Vitamin D production is not climate but the amount of time spent indoors. The relatively minor variation in sunlight due to the angle of the sunlight is dwarfed by the massive variation in lifestyle of primarily indoors groups vs. primarily outdoors ones. At best you could argue that people in cold climates are more likely to spend their days indoors.
Skin color also correlates poorly with temperature. While we tend to have a simplistic "Sweden cold, Africa hot" notion, if skin color was meaningfully correlated with cold weather we'd expect tribes of pale-skinned people at high elevations in Africa. We'd also find it unusual that cold weather Koreans were considerably lighter than warm weather Indians.
I'm curious if there's really any scientific foundation for your points - it seems like the sort of assumptions the eugenicists used to make about race.
I can cite my literature review for you, again these are anthropology studies, which is now under biological anthropology or evolutionary biology.
Important point here: a lot of the prevailing ideas about our evolutionary history is based on assumptions, because we don’t have any living specimens of our evolutionary ancestors. How would we ever actually test these ideas with the scientific method.? This research relies a lot of comparisons, correlations, and associations with modern populations as proxy groups understanding that the conclusions may not be 100% accurate. Just because the methods aren’t the epitomized gold standard of science doesn’t mean they are invalid, incorrect, or to be ignored.
Also, anthropology as a discipline started in the 1800: as a “science” to prove racial difference separated humans into distinct species as a way to encourage slavery and as you mentioned eugenics. While that history cannot be erased, papers and research evaluating racial differences in such a way are no longer in circulation and no longer cited or built upon, they have been rejected and dismissed after numerous studies disproved the premises. I did in another post discuss the concept that head size and or brain size is not an indicator of intelligence for this purpose, similarly to why I explained melanin as functional for sun exposure and Vitamin d production, taking them out of the context of eugenics and placing them in the context of physiological function where they belong.
Moving on. Wearing clothing and indoor living are behaviors of modern humans/ homo species, only within the last 300,000 approx. years human evolution as far as the evidence we have extends back 7 million years. Behaviors are studied by cultural anthropologists and archaeologists and are not in my scope of research. However, when we are talking about biological adaptations, that is adaptations and variations in anatomy and physiology, we have to consider a much larger timeline of human evolution. What did we start with and how has it changed.
On body shape-
It’s important to note that shape is not the same as size, it involves relationships in different directions (long AND narrow, short AND broad) your points about the tallest people are more of a size indicator because we don’t have any information about the body shape from just height, are the lean or stout? Anyway
Bergman’s rule and Allen’s rule are the two guiding rule for my statements. They are well documented.
Here are some sources:
Ruff, Christopher B. 1993. Climatic adaptation and hominid evolution: the thermoregulation imperative. Evolutionary Anthropology
*Chris Ruff writes a lot of body morphology and climatic adaptation.
Beals, KL; CL Smith, SM Dodd. 1984. Brain size, cranial morphology, climate, and time machines.
Daniel Lieberman- Story of the Human Body
DeMenocal, PB. 2011. Climate and Human evolution
…. To be continued I’m sleepy.
> only within the last 300,000 approx.
Pale skin emerged in a similar time frame. However, going that far back you're talking mostly about pre-human species. More importantly, you're talking about pre-human species that didn't live outside of temperate zones.
If cold = pale skin, then how did pale skin emerge hundreds of thousands of years before settlement of cold regions?
> Bergman’s rule and Allen’s rule are the two guiding rule for my statements.
I believe you're misusing them. They're intended for discussions of speciation, not minor variations within a single species.
> Climatic adaptation and hominid evolution: the thermoregulation imperative.
Your original point was about modern human beings and the variations we see, not about pre-human species that evolved into humans.
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Not even just genetically, people become acclimatized over time. We see this when less hot locations experience heatwaves, even when the temperatures remain below what hotter locations experience routinely, the rates of heat stroke still rise, which isn't ethnically disparite.
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mixer99 t1_j1e3nd1 wrote
Absolutely. Darker skin has more melanin, which offers more protection from harmful sun rays. As people started migrating into Europe, where the sun shines a lot less, it became more important to have lighter skin that makes vitamin d more efficiently.