Saturday, March 11, 2017

Wisdom Of The Week

The things that we thought we understood about Europeans are coming unstuck as we examine the genes of more ancient people. For example, it was generally accepted that pale skin evolved so we could get more vitamin D after moving north to where there was little sun and people had to cover up against the cold. But it turns out that it was the Yamnaya people from much further south, tall and brown-eyed, who brought pale skins to Europe. Northern Europeans before then were dark-skinned and got plenty of vitamin D from eating fish.

It is the same with lactose tolerance. Around 90 per cent of Europeans have a genetic mutation that allows them to digest milk into adulthood, and scientists had assumed that this gene evolved in farmers in northern Europe, giving them an additional food supply to help survive the long winters. But Eske’s research using the genomes of hundreds of Bronze Age people, who lived after the advent of farming, has cast doubt on this theory too: “We found that the genetic trait was almost non-existent in the European population. This trait only became abundant in the northern European population within the last 2,000 years,” he says.

It turns out that lactose tolerance genes were also introduced by the Yamnaya. “They had a slightly higher tolerance to milk than the European farmers and must have introduced it to the European gene pool. Maybe there was a disaster around 2,000 years ago that caused a population bottleneck and allowed the gene to take off. The Viking sagas talk about the sun becoming black – a major volcanic eruption – that could have caused a massive drop in population size, which could have been where some of that stock takes off with lactose.”

While ancient genomics can help satisfy curiosity about our origins, its real value may be in trying to unpick some of the different health risks in different populations. Even when lifestyle and social factors are taken into account, some groups are at significantly higher risk of diseases such as diabetes or HIV, while other groups seem more resistant. Understanding why could help us prevent and treat these diseases more effectively.

It had been thought that resistance to infections like measles, influenza and so on arrived once we changed our culture and started farming, living in close proximity with other people and with animals. Farming started earlier in Europe, which was thought to be why we have disease resistance but Native Americans don’t, and also why the genetic risks of diabetes and obesity are higher in native Australian and Chinese people than in Europeans.

“Then,” says Eske, “we sequenced a hunter-gatherer from Spain, and he showed clear genetic resistance to a number of pathogens that he shouldn’t have been exposed to.” Clearly, Europeans and other groups have a resistance that other groups don’t have, but is this really a result of the early agricultural revolution in Europe, or is something else going on?

Eske’s analysis of people living 5,000 years ago has also revealed massive epidemics of plague in Europe and Central Asia, 3,000 years earlier than previously thought. Around 10 per cent of all skeletons the team analysed had evidence of plague. “Scandinavians and some northern Europeans have higher resistance to HIV than anywhere else in the world,” Eske notes. “Our theory is that their HIV resistance is partly resistance towards plague.”

It could be that the cultural changes we have made, such as farming and herding, have had less influence on our genes than we thought. Perhaps it is simply the randomness of genetic mutation that has instead changed our culture. There’s no doubt that where mutations have occurred and spread through our population, they have influenced the way we look, our health risks and what we can eat. My ancestors clearly didn’t stop evolving once they’d left Africa – we’re still evolving now – and they have left an intriguing trail in our genes.

What Does It Mean To Be Human?

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