Great question. Normally, we expect people with norther ancestors to have light skin for two reasons: A. because having lighter skin allows people to make vitamin D, which allows them to absorb calcium for strong bones and teeth and B. because they have less chance of sunburn than people who live closer to the equator, so they may need pigment less.
Let’s look at the vitamin D issue first. Lack of vitamin D leads to a deficiency disease called rickets. People with rickets have weak bones and bowed legs. Let’s make a prediction.
If Inuit people weren’t getting enough vitamin D, skeletons from Inuit people who died hundreds of years ago (before vitamin supplements) should show signs of rickets. They don’t. So where were those people getting their vitamin D? It turns out that eating a lot of fish and marine mammals means a diet high in vitamin D. Now that Inuit people have a less traditional diet, they may need other sources of vitamin D, such as fortified milk.
Some scientists also note that Inuit people can have vitamin D levels that are lower than “normal” for other groups of people without showing symptoms of rickets. This may be because their ancestors adapted to needing less vitamin D. Populations have a lot of variation due to random mutation. So there was probably variation in the amount of vitamin D people needed. People who needed a lot of vitamin D may have left fewer offspring than people who didn’t. One thing I want to be really clear about is that mutations are random. They don’t happen because we need them.
So is there any advantage to having darker skin if you live in the far north? Actually, sunburn is a major issue on snow and ice because you get glare from the sun and from the reflection off the sun off the snow and ice. Having darker skin around the eyes may also lead to less reflection to the eyes (athletes sometimes darken the skin under their eyes to avoid this glare).
Remember too that Inuit people can tan due to exposure to the sun. So if they are out on the ice and snow a lot, they will have darker skin than their family members who stay inside more. Changes that happen during your life are not passed down. That is, tanning does not lead to darker offspring any more than losing a toe causes you to have a 9-toed baby.
What other adaptations can you think of that people or other animals might have to living in the Arctic?
Thanks for asking,
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