[阅读小分队] 【揽瓜阁5.0】Day3 2021.02.10【自然科学-生物、物种、生物】

It is a common assumption that migrants have more pizzazz than stay-at-homes. That this is reflected in people’s genes, though, may come as a shock. Yet this is the conclusion of a study based on almost half a million Britons who have volunteered to have their dna, and much else about them too, recorded in the uk Biobank, a resource available to researchers who are trying to understand the links between genetics, environment, disease and social outcomes.

The study in question, just published in Nature Human Behaviour, was carried out by a team led by Abdel Abdellaoui of the University of Amsterdam, in the Netherlands, and Peter Visscher of the University of Queensland, in Australia. Building on previous work done in the Netherlands, they were looking at how genetic patterns associated with certain biological, medical and behavioural traits cluster geographically and change as people move around.

To establish baselines for their work, Dr Abdellaoui, Dr Visscher and their colleagues turned first to 33 published studies that used a technique called genome-wide association study. This is intended to discern the contributions to a trait of large numbers of genetic differences that each have a small effect. It concentrates on so-called single-nucleotide polymorphisms (snps)—places in the dna where an individual genetic “letter” routinely varies from person to person. There are, for example, about 100,000 snps that affect height. On average, each makes a contribution, either positive or negative, of 0.14mm to someone’s adult stature. This is in contrast to Mendelian variations, where a single difference between individuals has a pronounced effect—such as the difference between brown and blue eyes.

Each of the 33 baseline studies identified large numbers of snps that had positive or negative effects on a particular trait: extroversion, heart disease, height, body fat, age at menopause, recreational drug use and so on. The researchers then applied these snp patterns to the records of 450,000 uk Biobank participants, and asked various questions. One thing they looked for was geographical clustering of snps related to individual traits. This, they discovered in abundance. Of the 33 traits under consideration, 21 showed evidence of snp-related geographical clustering.

The most strongly clustered of all, they found were snps for educational attainment (ie, how many years an individual had spent at school and college). snps lowering educational attainment were particularly clustered in former coal-mining areas. These are places that have seen a lot of internal migration, both inward, when the mines were developed during the late 18th and 19th centuries, and outward, after the second world war, as mining shrank from being one of Britain’s biggest employers to its current state of near non-existence.

Dr Abdellaoui and Dr Visscher were able, from their studies of the biobank’s records, to chart the effects of the more recent, outward migration. They divided participants into four groups: those born in mining areas who had subsequently left; those born in mining areas who had stayed; those born outside mining areas who had moved into one; and those who had never lived in a mining area. The results were stark. People in the first group, outward migrants from mining areas, had significantly more educational-attainment-promoting snps, and fewer damaging ones, than any of the other groups, while people in the second group, stay-at-homes in mining areas, had the opposite.

Though not quite so sharply as with educational achievement, this pattern was also reflected in all but one of the other 20 snp-related traits the researchers looked at. With the exception of bipolar disorder, the best outcomes were found in outward migrants from coalfields and the worst in stay-at-homes. The healthy, in other words, depart. The less healthy remain.

The upshot is a vicious spiral. That young, ambitious, healthy people tend to leave economically deprived areas is hardly news. But to see that written clearly in their dna, which they take with them when they leave, while the converse is written in the dna of those who stay behind, raises questions of nature and nurture that society is ill-equipped to answer, and possibly unwilling to confront.

Dogs were the first animals to be domesticated. And they stuck with us as we changed lifestyles from hunting/gathering to farming to city living.

“The dog is a species that is intimately linked to human history.”

Anders Bergström, a postdoc at the Francis Crick Institute in London. He and his colleagues studied the genomes of 27 ancient dog bones dug up around the world. They found that by 11,000 years ago:

Bergström: “We see that the dog started to diversify genetically. So we find evidence of at least five major lineages of dogs already at this time.”

Dog remains have been found in Europe, Asia and the Americas in a pattern similar to how humans moved and mixed.

Bergström: “To a large degree the history of dogs seems to have been shaped by human history, so likely reflecting how when humans moved they would have brought their dogs with them.”

Ancient humans clearly found dogs to be very useful.

Bergström: “In the Arctic there's evidence that sled dogs actually emerged very early and people used them for the particular purpose of sledding, perhaps as early as 10,000 years ago.”

A few modern breeds—like the African Basenji, New Guinea Singing Dog or Australian Dingo—are similar to one of the five ancient lineages. Most other modern breeds derive at least in part from European dogs, which came to dominate dog genomes.

Bergström: “If you go back four or five thousand years ago there's a great diversity of dogs in Europe, but at some point there was probably a single population that expanded and basically replaced other populations in Europe. This was something that we did not predict, and you couldn't really see just from studying archaeology. But when we look at the DNA we see that there's all this diversity in the past that is not represented in present day dogs.”

The study is in the journal Science, where you’ll find maps of dog migrations over time.

One odd finding: about 11,000 years ago it looks like dogs spread more widely than humans did.

Bergström: “That's actually a process we don't really understand. So how could the dog spread so quickly and widely? We're not aware of any human migrations at this time that could have facilitated the spread of the dog but somehow it spreads very quickly to human groups all across the world, perhaps because it was a very useful thing for these early human hunter-gatherer groups.”

Humans were also useful to dogs. Prehistoric Petcos didn’t exist, so dogs probably ate what humans did. And as humans started to farm, both species quickly adapted to digest more grains. The number of copies of a starch-digesting gene in both humans and dogs increased in the generations following the invention of agriculture.

Bergström: “Yeah, so that's a very striking example of convergent evolution between humans and dogs…in a way it's kind of interesting to think of the dog as a kind of an evolutionary experiment that runs alongside human history and undergoes the same lifestyle changes that we do.”