Wednesday, March 22, 2017
A new study of hundreds of human genomes has revealed that groups in various regions of the world have evolved for diets with different amounts of meat and vegetables
People from Europe, particularly its southern regions, are optimized for a high-plant diet. But people from other areas, such as the Inuit of Greenland, have a biochemistry that is better able to process lots of meat fat. UC Berkeley integrative biology professor Rasmus Nielsen and his colleagues had access not only to hundreds of genome sequences from humans today, but also to sequences from 101 people who lived in Europe 5,000 years ago during the Bronze Age. By comparing these genomes, they found that two particular regions of DNA were under intense selection over the past several thousand years and changed rapidly in response to evolutionary pressures. These DNA regions contain two genes called "fatty acid desaturase 1 and 2," or FADS1 and 2 for short. The FADS genes regulate how the human body converts short-chain poly-unsaturated fatty acids (PUFAs) into long-chain PUFAs for the health of many tissues, including muscles and the brain. In Europeans dating back to the Bronze Age, the FADS genes have undergone mutations to produce more long-chain PUFAs. This suggests a diet higher in vegetables and grains, which produce short-chain PUFAs. Meat produces long-chain PUFAs. The Inuit group's FADS genes are primed to produce fewer long-chain PUFAs, likely because the Inuit diet is so high in animal fats from ocean mammals. Nielsen and his colleagues believe that the European variant of the FADS genes likely are the result of agricultural lifestyles, leading to diets rich in wheat and vegetables. When people in Europe and the Middle East began to practice farming over 10,000 years ago, suddenly they were ingesting far more of those short-chain PUFAs. People who could convert short-chain PUFAs into long-chain PUFAs efficiently were more likely to survive, and so their FADS genes were passed on. It's also likely that the FADS genes have been changing rapidly for tens of thousands of years, as humans found new environmental niches across the planet. This puts them in stark contrast with genes that allow for lactose tolerance, which are clearly linked to a rise in dairy production on farms in the West. "The selection associated with lactase persistence (avoidance of lactose intolerance) seems to have been stronger in Northern Europe," Nielsen explained. "However, we don't see the same geographic patterns for the FADS genes. If anything, selection that would be driven by a more vegetarian diet might have been stronger in Southern Europe. Selection associated with the FADS genes might also be older than the selection affecting lactase." So there is little overlap between people with veggie-friendly FADS genes and people with genes for lactase persistence.