I realised that for some reason, I still don’t know this. Why do we have different skin colors, hair textures, eyes or such? Is it just a random thing that happened or are there evolutionary reasons to it?
Without the evolutionary pressure to maintain high melanin levels in the skin, and possibly also from interbreeding with Neanderthaal, European people’s got paler.
Someone mutated to have eyes that were paler and more sensitive to light, which was useful during the longer nights further north, and that mutation spread.
So it’s a bit of both.
Put differently (so as not to imply high melanin is fundamentally superior):
Someone mutated to have lower melanin levels in their skin, which was useful to absorb more sunlight for Vitamin D production further north, and that mutation spread.
Without the evolutionary pressure to maintain high melanin levels in the skin, and possibly also from interbreeding with Neanderthaal, European people’s got paler.
But what’s the evolutionary pressure keeping melanin levels among ethnicities that stayed black? And why does it affect people in Central and South Africa but not in North Africa and the Middle East, when both regions are about equally hot?
It’s important to think about the time scale that evolution works on. These changes happened very slowly 50,000+ years ago.
The regions near the equator where people still tend to be lighter skinned have been in contact with and interbreeding with lighter skinned people for thousands of years, plus many migrations and invasions.over the past 10,000 years.
Most likely a conbination of the amount of sun exposure and other poaitive genetic mutations that happened alongside melanin levels.
An example of the complexity of genetic changes being intertwined is resistance to malaria and sickle cell anemia. The benefits of resistance to sickle cell anemia outweigh the negstives of the increased chance of sickle cell anemia so the mutation has persisted.
It is likely that North African populations had something that was beneficial as a tradeoff for their comparably lighter skin. Wearing clothing that covers a lot more of their body and having shelters from the sun could also help to mitigate some of the sun damage.
So it is complicated and most differences are due to a combination of genetic traits, they don’t get passed down one trait at a time.
Skin color is directly related to latitude. Darker skin means more melanin, which absorbs more light and protects against sunburns and thus skin cancer.
Eye color factors are less confidently known, but darker eyes generally have a better time in bright daylight.
Regarding those two, it’s also worth mentioning that the Inuit people don’t follow those patterns, as while they have less sunlight, they also have to deal with reflected light off the snow.
Hair texture is like eye color in that we’re only mostly confident, but tight curls also probably protect from the sun.
It’s also been posited that epicanthic folds might help against freezing winds, but there’s no real evidence for that.
“Evolutionary reason” does not necessarily mean that a feature is an advantage. Mutations are random and then positive or negative selective pressure act on them untill the mutation is either extinct or is adopted by the whole population. For features without selective pressure the same thing still happens it just takes longer and is basically random. So different populations of a species will always develop different features even when given the same environment.
So for most of the features you listed: yeah it just happened.
the simple reason is geographic isolation of populations. over time groups of people in different places gain minute genetic differences relating to their region/breeding population.
its geography + genetic drift
Some features, such as melanin levels, are due to evolutionary pressures. High levels of melanin protect you from the sun, lower levels of melanin boost your vitamin D production.
Other features are just random. Over time, human populations were affected by random changes that weren’t exactly useful but not detremental either. They’re called sprandels. According to a quick Google search, blue eyes don’t seem to have any advantages, but not really any major disadvantages either, so that would be an example of that.
For height and weight, there are links to the climate that the people live in. Typically, hotter climates favor skinny people while colder climates favor more husky people. As for height, my understand is that a dry heat favors taller people as they can take advantage of sweating more than a wet heat.
I think the impact of wealth and access to nutrition and an environment that does not stunt development plays a major role here as well. A good example of this is height in Europe post-industrial revolution and improvements in medicine:
Most notable being a 20cm increase in the Netherlands in just over 100 years as well as changes in places that industrialised quickly like China:
Not to say that geography plays no role but it’s closer to 10cm gap than a 30cm one.
