Human populations evolved in a similar way after we started farming

A study combining a growing number of ancient genomes from living humans has given us the best picture yet of how humans have evolved over the past 10,000 years. It shows that people in different parts of the world evolved in similar – and sometimes even identical – ways after we adopted agriculture.

“Some of the same traits and the same genes are under selection in different populations,” he says Laura Colbran at the University of Pennsylvania.

Evolution occurs when a genetic variant becomes more common in a population—usually, but not always, because it confers an advantage. By comparing human genomes, we can then find signs of recent human evolution.

The genomes of long-dead people are particularly useful, Colbran says. “Ancient DNA allows us to look at genetic history live, while many other methods try to infer it.”

Studies of recent evolution have focused on Europe because that is where researchers have collected the oldest and most modern genomes. But Colbran’s team used the growing number of genomes from non-European countries to take a broader look at more than 7,000 ancient and modern genomes. Ancient genomes mostly come from the last 10,000 years, while modern ones come from living people.

Essentially, the team used ancient genomes to predict what modern genomes would have been like if there had been no evolution, and then looked for differences—signals of selection. They found 31 in total, and many of them were shared—that is, peoples in different parts of the world evolved in similar ways, most likely due to the independent adoption of agriculture around the world around the same time.

For example, less than a quarter of the oldest people had a genetic variant that increases expression FADS1 gene. The FADS1 enzyme converts short fatty acids common in plants to longer fatty acids common in meat, so more of the enzyme is thought to benefit people with a more plant-based diet. The FADS1-amplifying variant is now present in more than three-quarters of people in Europe, Japan and northern China. The team found that in Europe, the strength of selection has remained constant over the past 300 generations, but has increased in East Asia over the past 100 generations.

Then there is the enzyme alcohol dehydrogenase 1B, encoded by the gene ADH1B. It is well known that the variant ADH1B which rapidly converts alcohol to acetaldehyde, causing unpleasant symptoms such as facial flushing, has become common in East Asia. It is believed that this variant was chosen because it discourages drinking. “It’s the strongest selection signal you’ve seen in East Asia,” says Colbran.

This variant did not exist in ancient Europeans, but her team still found evidence of strong selection involving the ADH1B enzyme. “There’s something that changes the amount earned or how it reacts,” says Colbran. More work will be needed to determine the exact variant and what it does, but it is almost certainly an adaptation to drinking alcohol.

The team even looked at traits that are influenced by multiple genetic variants, such as a person’s waist-to-hip ratio. An increase in waist-to-hip ratio is associated with higher fertility, so you might think there would be selection for it.

Instead, the team found that there appears to be strong selection that keeps women’s waist-to-hip ratios within certain parameters. “It’s really interesting in that we’re seeing stabilizing selection,” says Colbran.

Waist-to-hip ratio varies among different populations, but findings suggest that the optimal value is somewhere in the middle, he says. “Population to population, it can change depending on the exact context.”

It’s an exciting study that involves a lot of ancient DNA that hasn’t been analyzed before, he says Alexander Gusev at Harvard University. “The authors found that variants under selection in one population are significantly enriched for being under selection in other populations,” says Gusev. “I take it that selection is likely to be parallel across populations. It’s been hypothesized, but it hasn’t been proven yet.”

Yassine Soulmi at the University of Adelaide in Australia, says the team’s approach was able to identify regions of the genome not previously known to be under selection, in addition to previously identified regions. “Their new method takes full advantage of the large amount of ancient DNA that is now available,” says Souilmi.

The results are the tip of the iceberg, says Colbran. As more genomes are sequenced – especially more non-European ones – we will find much more evidence of recent evolution.

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