European genes assembled by a need for vitamin D
When humans moved into Europe 40,000 years ago, it’s assumed they arrived with dark skin. It’s also been assumed that they quickly started selecting for lighter skin in their new, Northern climate. Then, the thinking continued, after figuring out farming, this population started propagating genes for lactose tolerance, taking advantage of milk from the newly domesticated livestock. But DNA studies of European populations have been unraveling this tidy little story, revealing a more complicated and more recent timeline.
The genes researchers were looking for were those involved in a few different, and apparently discrete, traits. These included the LCT gene allowing the digestion of sugars in milk, SLC24A5 and SLC45A2, leading to pale skin, and HERC2/OCA2, which is the source of blue eyes, as well as possibly influencing lighter hair and skin pigmentation. And while it could have been possible to have all of these genetic changes sweep newly-settled Europeans all together, they seem to have come in multiple waves of influence from multiple sources.
Eating cheese and milk a fresher concept than previously understood
The new timeline starts with hunter-gatherers 8000 years ago, who were confirmed to not carry the LCT gene allowing lactose tolerance. This genetic variation wouldn’t take root until 2200 BCE, 5000 years after Europeans had been practicing agriculture. Two waves of immigrants that did bring many farming practices also lacked the gene upon arrival, indicating it may have developed in Europe. The advantage of consuming dairy went beyond gaining another source of calories- vitamin D was relatively scarce in Europe compared to humans’ original habitat further south, and milk products would have helped compensate for the loss of sunlight.
Soaking up any available sun
The need for vitamin D likely drove the propagation of genes for pale skin as well. Darker skin blocks more ultraviolet light than lighter skin, which, when less sunlight is available at higher latitudes, leads to a drop in the body’s synthesis of vitamin D. So while Southern Europeans were had dark skin until at least 5800 years ago, populations in the north were found to carry genes for lighter skin and lighter eyes as far back as 7700 years ago. It wasn’t until farmers from the Near East, who also had genes for lighter skin, immigrated to Europe that these variations started to spread across the whole continent.
So the piecemeal story of both diary consumption and pale pigments may still have the one common thread— vitamin D. While vitamin D does play a role in our immune system, other genes for immune response didn’t seem to be pressured or propagated in the European population in the same way, even with the introduction of farming, animal husbandry, and new populations. All that mattered was making up for the loss of sunshine.
Source: How Europeans evolved white skin by Ann Gibbons, Science
