why do Nordic people have fair hair, if it’s less sunny where they live, whereas southern people have dark hair, and it’s generally more sunny where they come from?


Don’t mean to be stereotypical. But generally people from northern countries (especially EU) tend to have blond / fair hair, whereas southern people have darker hair. Yet when it’s summer and sunny, your hair tends to get lighter, so you’d think that southern people should have lighter hair and northern people that are less exposed to the sun should have darker hair.

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Well there are two components to this.

1. It’s an evolutionary trait that helps people live in that climate

2. it’s a sexually selected trait, meaning people just prefer one color so they’re more likely to mate with someone that has that trait, so it becomes more common in the population.

Long answer

As animals evolve those who are best suited to an environment are more likely to survive so their traits are passed on and more animals will have those some traits. Dark colors protect better against the sun and absorb more of the light preventing it from damaging the skin that’s under it than lighter colors. This is also why people in southern or hot sunny climates tend to have darker skin tones than those from northern cooler climates. The lightening you see in the summer is actually from damage to the hair, it basically bleaches out the melanin or color in the hair into nothing making it closer and closer to white or grey. The reason that hair lightens and skin darkens just happens because like clothing fibers, hair is already “dead” and can’t rebuilt itself, skin is still alive in a sense so it changes in response to the environment.

As for sexual selection, all animals and people have a preference, whatever is the most common preference is what starts becoming more and more common.