Eli5: what was the main reason why there are differences in facial structures of different races?
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Bc this gene was strong and this gene was weak. Different regions meant different gene pools. We all used to marry our siblings.
Because of their (historical) different locations. Which made people adapt to whatever conditions they were in
Because of spending a long time genetically isolated from each other, and also experiencing different conditions during this time.
Just being genetically isolated even in the same conditions can make two groups of people start to look different for no real reason at all. Sometimes genes just drift.
But different conditions would likely apply some sort of pressure on this drift. For example, it is hypothesized that the caucasian’s longer nose is meant to help with breathing cold and dry air. A longer nasal passage helps to moisturise and warm up the air before it enters our sensitive lungs. Someone with a shorter nose may be more susceptible to respiratory infection in cold climates.
There’s also the tendency of caucasians to be shorter and stockier than africans. This helps with body temperature regulation. If it’s very hot, you want a large surface area and low body volume to cool off efficiently. This is most easily achieved by long and slender limbs. If you’re trying to conserve body heat, it’s better to be as spherical as possible, i.e. shorter limbs and bigger body.
Another major difference between asians/africans and caucasians is the genetic heritage. A quite large part of caucasians have a sizable chunk of neanderthal DNA, up to 3-4% IIRC. Africans and asians typically do not possess these genes, since their ancestors were never in contact with neanderthals. This would certainly affect a lot of things.
There are probably millions of these types of factors that have ultimately led to the races we see today, and a large part of them are probably entirely random and without any conceivable “reason”.
It’s a mistake in the first place to think “race” is a thing but genetic differences between places can obviously produce differences in appearance.
Genetic drift has caused some slight but noticable differences to the bone structure (and therefore facial structures) of the various races. Most likely just random chance unlike skin tone which lines up 1:1 with the amount of average sunlight an area gets (and therefore vitamin D).
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