Ancient DNA reveals how Europeans developed light skin and lactose tolerance

June 11, 2015 by Daniel Zadik, The Conversation
Slurp and thank the Yamnaya. Credit: Samantha Jade Royds/Flickr, CC BY-SA

Food intolerance is often dismissed as a modern invention and a "first-world problem". However, a study analysing the genomes of 101 Bronze-Age Eurasians reveals that around 90% were lactose intolerant.

The research also sheds light on how modern Europeans came to look the way they do – and that these various traits may originate in different ancient populations. Blue eyes, it suggests, could come from in Mesolithic Europe (10,000 to 5,000 BC), while other characteristics arrived later with newcomers from the East.

About 40,000 years ago, after modern humans spread from Africa, one group moved north and came to populate Europe as well as north, west and central Asia. Today their descendants are still there and are recognisable by some very distinctive characteristics. They have light skin, a range of eye and hair colours and nearly all can happily drink milk.

However, exactly when and where these characteristics came together has been anyone's guess. Until now.

Clash of cultures

Throughout history, there has been a pattern of cultures rising, evolving and being superseded. Greek, Roman and Byzantine cultures each famously had their 15 minutes as top dog. And archaeologists have defined a succession of less familiar cultures that rose and fell before that, during the Bronze Age. So far it has been difficult to work out which of these cultures gave rise to which – and eventually to today's populations.

The Bronze Age (around 3,000–1,000 BC) was a time of major advances, and whenever one culture developed a particularly advantageous set of technologies, they become able to support a larger population and to dominate their neighbours. The study found that the geographical distributions of genetic variations at the beginning of the Bronze Age looked very different to today's, but by the end it looked pretty similar, suggesting a level of migration and replacement of peoples not seen in western Eurasia since.

Ancient DNA reveals how Europeans developed light skin and lactose tolerance
Yamnaya skull. Credit: Natalia Shishlina

One people that was particularly important in the spread of both early Bronze-Age technologies and genetics were the Yamnaya. With a package of technologies including the horse and the wheel, they exploded out of the Russian and Ukrainian Steppe into Europe, where they met the local Neolithic farmers.

By comparing DNA from various Bronze-Age European cultures to that of both Yamnaya and the Neolithic farmers, researchers found that most had a mixture of the two backgrounds. However the proportions varied, with the Corded Ware people of northern Europe having the highest proportion of Yamnaya ancestry.

And it appears that the Yamnaya also moved east. The Afanasievo culture of the Altai-Sayan region in central Asia seemed to be genetically indistinguishable from the Yamnaya, suggesting a colonisation with little or no interbreeding with pre-existing populations.

Mutations traced

So how have traits that were rare or non-existent in our African ancestors come to be so common in western Eurasia?

The DNA of several hunter gatherers living in Europe long before the Bronze Age was also tested. It showed that they probably had a combination of features quite striking to the modern eye: dark skin with blue eyes.

Ancient DNA reveals how Europeans developed light skin and lactose tolerance
Reconstruction of a Yamnaya person from the Caspian steppe in Russia about 5,000-4,800 BC.

The blue eyes of these people – and of the many modern Europeans who have them – are thanks to a specific mutation near a gene called OCA2. As none of the Yamnaya samples have this mutation, it seems likely that modern Europeans owe this trait to their ancestry from these European hunter gatherers of the Mesolithic (10,000-5,000 BC).

Two mutations responsible for light skin, however, tell quite a different story. Both seem to have been rare in the Mesolithic, but present in a large majority by the Bronze Age (3,000 years later), both in Europe and the steppe. As both areas received a significant influx of Middle Eastern farmers during this time, one might speculate that the mutations arose in the Middle East. They were probably then driven to high levels by natural selection, as they allowed the production of sufficient vitamin D further north despite relatively little sunlight, and/or better suited people to the new diet associated with farming.

Another trait that is nearly universal in modern Europeans (but not around the world) is the ability to digest the lactose in milk into adulthood. As cattle and other livestock have been farmed in western Eurasia since long before, one might expect such a mutation to already be widespread by the Bronze Age. However the study revealed that the mutation was found in around 10% of their Bronze Age samples.

Interestingly, the cultures with the most individuals with this mutation were the Yamnaya and their descendents. These results suggest that the mutation may have originated on the steppe and entered Europe with the Yamnaya. A combination of natural selection working on this advantageous trait and the advantageous Yamnaya culture passed down alongside it could then have helped it spread, although this process still had far to go during the .

This significant study has left us with a much more detailed picture of Bronze Age Europeans: they had the and range of eye colours we know today. And although most would have got terrible belly ache from drinking milk, the seeds for future lactose tolerance were sown and growing.

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11 comments

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Milou
not rated yet Jun 11, 2015
So, we are basically all emigrants over powering one another. And, we have evolved the way we are! Would someone please help our human race?
Torbjorn_Larsson_OM
5 / 5 (2) Jun 12, 2015
Interesting point on light skin - which seems an Asian derivative in major cases (Europeans, Asians) - the promotion could have been both variation (the mutation didn't happen in Europe, perhaps because of smaller populations) and selection (it takes both high latitudes and farming, lack of meat D vitamin intake).

Speaking of which, that was the point of another article on this, many people use milk, but fermentation (which the Yamnaya did) means there is little selection on lactose tolerance. However when you start to starve, you run out of fermented stock and have to try raw milk. If you get diarrhea in a weakened state, it is likely to kill or damage. Starvation periods, which Europe has been famous for, would be a powerful selective bottleneck.
Torbjorn_Larsson_OM
5 / 5 (3) Jun 12, 2015
@Milou: Help with what?

If you mean violence, the population density tells us immediately that modern humans are among the most peaceful animals there is. We are self socialized to a previously unobserved degree, and may even be the most peaceful ape. Due to poor statistics, bonobos are still out as possibly the most peaceful, they do have a culture that promotes it.

But now so do we. See e.g. Pinker's book on how violence has decreased to historically low levels. (I hear for reasons not too well understood, but the time horizon may imply cultural rather than genetic causes. Myself, I blame the Enlightenment and democracy for the lowest frequencies of violence, but the down trend likely started before that.)
Daniel Zadik
not rated yet Jun 12, 2015
RE: "Interesting point on light skin - which seems an Asian derivative in major cases (Europeans, Asians) - the promotion could have been both variation (the mutation didn't happen in Europe, perhaps because of smaller populations) and selection (it takes both high latitudes and farming, lack of meat D vitamin intake)."

Several different mutations can lighten the skin, and it appears that the two in the article are responsible to a large extent in Europe and western Asia, but other mutations do a similar thing in east Asia, and yet others did the job in Neanderthals. The selective pressure is likely the same (probably one or both of the ones you list), but it will work perfectly well on any of these mutations that it can get its hands on.
Doug_Huffman
not rated yet Jun 12, 2015
Each with 15 minutes as top dog; good for Eurasians, bad for Amerind abos. How values shift with the argument.
Daniel Zadik
5 / 5 (1) Jun 12, 2015
RE: "good for Eurasians, bad for Amerind abos. How values shift with the argument." Not sure I follow. I imagine its a very traumatic time for any population when it comes into contact with another that has superior technology. I would guess this is a universal law across space and time, but we see and hear the more recent examples more vividly for obvious reasons.
non-white majority
1 / 5 (1) Jun 12, 2015
It is indeed a very traumatic time when people with superior technology meet up with people of inferior technology, look at the "indigenous" "Europeans", they were absolutely conquered by these two waves of migrants.
non-white majority
1 / 5 (1) Jun 12, 2015
It is indeed a very traumatic time when people with superior technology meet up with people of inferior technology, look at the "indigenous" "Europeans", they were absolutely conquered by these two waves of migrants.
Captain Stumpy
5 / 5 (3) Jun 13, 2015
Monkeys can be easily controlled by other monkeys
@ren
this is true... it is also why religion is so successful... one big shot monkey controls the rest
Who can not love is a slave to the sin that wants to see other people in his unworthy condition. Its main characteristics are selfishness, pride and vanity. All because lack of love.
the rest of your pontification is pure unadulterated delusional gibberish

WTF does it even mean?
because you think science follows the evidence it can't love or be correct?
WTF?

you really should leave off your posturing and go back to violating religious forums with your diatribes... that is the only place it is welcome

THIS IS A SCIENCE SITE

if you want to condemn knowledge, go back to your church and tell everyone how we are all going to hell for finding out the truth about reality
Captain Stumpy
5 / 5 (3) Jun 13, 2015
This explains why proponents of evolution are so loud in public places.
@ren
this coming from the bible-shouting anti-science trolling poster pushing her religious dogma on a science site

the irony is killing me
ROTFLMFAO

thanks for the laugh, ren
had to downvote you, though...
simply because you are a liar and trying to push a false agenda which is not based upon science
Shootist
5 / 5 (2) Jun 13, 2015
So, we are basically all emigrants over powering one another. And, we have evolved the way we are! Would someone please help our human race?


The human race is doing just fine, thank you very much (your anti-survival nihilism notwithstanding).

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