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I noticed that many black-ish people I've met have bigger lips than the white-ish people I've met. However, not all black-ish people have big lips.

Is there any explanations in terms of natural selection, geographic localisation, common ancestors, or something else that could explain why a subset of dark skin people have bigger lips on average than pale skin people?

Edit: This question is different from the other one because the answer talks about the nose and its function (air temperature) linked to the environmental factors. I don't see how this applies to lips.

Julien__
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Regard this one as a comment

I prefer to cite some text form this website instead of providing the link only (as it could be removed).

In general, this pattern can be observed across the planet with the size of lips and nose decreasing as we move away from the equator towards the poles. So what could the reason be?

For someone living in hot climatic conditions, cooling down the body is critical for their survival. Our body has many cooling mechanisms and one of them is simply disseminating heat when it comes in contact with colder air (simple thermodynamics). This however requires larger surface area so that more heat can be disseminated. 

Given that a significant portion of breathing also happens through the mouth (especially when exposed to heat), lips are pretty much like the gateway for colder air being inhaled and exhaled. So, the larger the lips, the more heat that can be disseminated. Thus, people living in hotter climatic conditions gradually evolved to have bigger lips. 

The opposite is true for people in colder climates. They get a survival advantage if they are able to retain as much heat as possible and so they gradually evolved to have smaller lips thus limiting the amount of heat that can escape when cold air brushes past their lips while inhaling and exhaling.

Notably, there was no scientific source provided for this claim, however intuitively this could make sense.

KingBoomie
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(This is an extended comment rather than an answer.)

One important thing to note is that depending on where you live, the "black-ish people you've met" may not be at all representative of black people worldwide. For example, if you live in the Western Hemisphere, then the large majority of the black people who live in your country are probably descended from Africans who lived in the so-called "Slave Coast of West Africa", which roughly comprised the modern-day nations between Sierra Leone and Nigeria. For example, here is a photograph of a present-day resident of Ghana (where many descendants of modern-day black inhabitants of the Western Hemisphere lived), and here is a photograph of a present-day resident of Eritrea. They look very different.

tparker
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