Two studies presented at the Biology of Genomes meeting here last week show how our genomes have changed over centuries or decades, charting how since Roman times the British have evolved to be taller and fairer, and how just in the last generation the effect of a gene that favors cigarette smoking has dwindled in some groups…
…With the help of giant genomic data sets, scientists can now track these evolutionary shifts in allele frequencies over short timescales….Pritchard’s team analyzed 3000 genomes collected as part of the UK10K sequencing project in the United Kingdom. For each allele of interest in each genome, Field calculated a “singleton density score” based on the density of nearby single, unique mutations. The more intense the selection on an allele, the faster it spreads, and the less time there is for singletons to accumulate near it. The approach can reveal selection over the past 100 generations, or about 2000 years.
Stanford graduate students Natalie Telis and Evan Boyle and postdoc Ziyue Gao found relatively few singletons near alleles that confer lactose tolerance—a trait that enables adults to digest milk—and that code for particular immune system receptors. Among the British, these alleles have evidently been highly selected and have spread rapidly. The team also found fewer singletons near alleles for blond hair and blue eyes, indicating that these traits, too, have rapidly spread over the past 2000 years, Field reported in his talk and on 7 May in the preprint server bioRxiv.org. One evolutionary driver may have been Britain’s gloomy skies: Genes for fair hair also cause lighter skin color, which allows the body to make more vitamin D in conditions of scarce sunlight. Or sexual selection could have been at work, driven by a preference for blond mates…
…In a sign of the method’s power, Pritchard’s team also detected selection in traits controlled not by a single gene, but by tiny changes in hundreds of genes. Among them are height, head circumference in infants, and hip size in females—crucial for giving birth to those infants. By looking at the density of singletons flanking more than 4 million DNA differences, Pritchard’s team discovered that selection for all three traits occurred across the genome in recent millennia.
Joseph Pickrell, an evolutionary geneticist at the New York Genome Center in New York City, has used a different strategy to put selection under an even keener microscope, detecting signs of evolution on the scale of a human lifetime. He and Przeworski took a close look at the genomes of 60,000 people of European ancestry who had been genotyped by Kaiser Permanente in Northern California, and 150,000 people from a massive U.K. sequencing effort called the UK Biobank…
..In the parents’ generation, for example, the researchers saw a correlation between early death in men and the presence in their children (and therefore presumably in the parents) of a nicotine receptor allele that makes it harder to quit smoking. Many of the men who died young had reached adulthood in the United Kingdom in the 1950s, a time when many British men had a pack-a-day habit. In contrast, the allele’s frequency in women and in people from Northern California did not vary with age, presumably because fewer in these groups smoked heavily and the allele did not affect their survival. As smoking habits have changed, the pressure to weed out the allele has ceased, and its frequency is unchanged in younger men, Pickrell explains. “My guess is we are going to discover a lot of these gene-by-environment effects,” Przeworski says.
Indeed, Pickrell’s team detected other shifts. A set of gene variants associated with late-onset menstruation was more common in longer-lived women, suggesting it might help delay death. Pickrell also reported that the frequency of the ApoE4 allele, which is associated with Alzheimer’s disease, drops in older people because carriers died early. “We can detect selection on the shortest timeframe possible, an individual’s life span,” he says
Differences in gut microbes, particularly early in life, are likely to contribute to a person’s susceptibility to autoimmunity. Vatanen et al. explored this phenomenon by comparing the microbiomes of children from Finland, Estonia, and Russia from birth to 3 years old. Russians have lower incidences of autoimmunity than Finns and Estonians, and their microbiomes early in life differed, too, with Finnish and Estonian children harboring larger amounts of Bacteroides species. The primary source of bacterial lipopolysaccharide (LPS), an immunomodulatory molecule, also differed among the children. Bacteroides-derived LPS, which probably dominates in Finnish and Estonian children, did a poor job of teaching immune cells self-tolerance in cell culture and in mice, suggesting that it may contribute to autoimmune susceptibility in these populations.
Cell 165, 842 (2016).
As the existence of animal personalities becomes undeniable, researchers face a puzzle: how disparate personalities can coexist in a single species. Europe’s great tits are helping explain how. At long-term field sites in Germany, the United Kingdom, and the Netherlands, Niels Dingemanse, a behavioral ecologist at the Ludwig Maximilian University of Munich in Germany, and others have manipulated the number of offspring in nests and the density of nest sites. They’ve found that different conditions favor opposite personalities, thereby enabling behavioral variation to persist.
When bird populations are dense, competition for territories, mates, and food sharpens, and one might expect aggressive individuals to win out. But when Dingemanse’s postdoc, Marion Nicolaus, tracked 541 adults for 4 years, recording which survived and how many young they produced, she found the opposite was true. It seems that when birds have to compete for scarce resources, the aggressive ones often get into fights, which take a physical toll. Aggressive birds also strain to keep all their young fed, further taxing their health. Thus, compared with more docile individuals, these birds are more likely to wear themselves out and fail to survive to the next breeding year. Only when densities are low do type A birds outcompete gentler ones and thrive, Dingemanse says.
The findings parallel predictions made a decade ago about humans: that “in growing populations, competitive environments should favor shy, non-explorative, non-aggressive individuals,” Nicolaus, Dingemanse, and colleagues write in an upcoming paper in Ecology Letters.
By looking for marked fish, they found that shy individuals hadn’t simply moved out of the groups; they had vanished, most likely because they were not aggressive enough to compete for food in the group and had starved, or were too slow in reacting to predators that homed in on the school. On their own, however, the shy fish thrived, because remaining still is an effective antipredator defense. Bold fish, in contrast, became targets when isolated.
The finding suggests that personality types could play a role in evolution by helping divide a species into separate populations. Such segregation can lead to further differentiation and, eventually, to reproductive isolation. “That is often the first step in models of speciation,” Duckworth says.
Anelosimus studiosus, a small, brownish U.S. spider, lives in groups of from two to two dozen individuals and can build car-sized webs capable of snaring a small bird or mammal. Over the past decade, behavioral ecologist Jonathan Pruitt of UC Santa Barbara has determined that not only do individual spiders have personalities—bold and active or docile and inactive—but also that the mix of the two types gives each colony a distinctive “group personality.” The group personality needs to fit the demands of the local environment if the colony is to survive, he and his colleagues reported in Nature in 2014.
Thus, group selection based on different mixes of personality variants in the population. Does the same hold for humans? Continuing the speculation from above, do the cuck and ethnocentric fractions of the White population form an integrated whole, with the problem being we have too high a cuck fraction? Will a change toward more ethnocentrics (if possible) solve the problem without complete elimination of the cucks, or a “speciation” between the groups?
In recent years, biologists have increasingly recognized that evolutionary change can occur rapidly when natural selection is strong; thus, real-time studies of evolution can be used to test classic evolutionary hypotheses directly. One such hypothesis is that negative interactions between closely related species can drive phenotypic divergence. Such divergence is thought to be ubiquitous, though well-documented cases are surprisingly rare. On small islands in Florida, we found that the lizard Anolis carolinensis moved to higher perches following invasion by Anolis sagrei and, in response, adaptively evolved larger toepads after only 20 generations. These results illustrate that interspecific interactions between closely related species can drive evolutionary change on observable time scales.