Human organ evolution (Introduction)

by David Turell , Friday, April 20, 2018, 15:16 (2191 days ago)

Deep divers have big spleens:

https://www.the-scientist.com/?articles.view/articleNo/52347/title/Free-Divers-From-Sou...

Researchers have identified a genetic variant that likely results in larger spleens among the Bajau people in Southeast Asia, conferring better endurance for free diving in the ocean. The study, published today (April 19) in Cell, is an uncommon example of natural selection in modern humans that likely occurred on the order of hundreds or thousands of years.

“'This is a fascinating example of how humans can, in a relatively short amount of time, adapt to a local environment,” says study coauthor Rasmus Nielsen of the University of California, Berkeley.

"The Bajau people live in villages scattered throughout Southeast Asia, spending much of their day using traditional spears and other simple equipment to collect fish and shellfish by free diving—holding their breath. They have subsisted on this hunting method for more than 1,000 years.

"The human body has a few tricks to increase the time spent underwater in an oxygen-deficient environment. One way is to boost red blood cell production, which allows for more efficient oxygen delivery to organs and tissues, or to expand their lung capacity. A third adaptation—which the authors describe for the first time today—is increasing the size of the spleen, which stores oxygenated red blood cells and contracts during diving to release the blood cells into circulation. (another article says it boosts oxygenated red cells by 9%)

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"Ilardo and her colleagues found that the spleens of the Bajau people were about 50 percent larger compared to the Saluans, even while taking into account individuals’ gender, age, weight, and height.

"Next, the team compared the genomic sequences of Bajau and Saluan participants to those of the Han Chinese as a control, unrelated group. Scanning for variants, the group identified the top 25 polymorphisms that were unique to the Bajau genomes, suggesting natural selection pressures were at work. The study authors created a phylogenetic tree, calculating that the Bajau and Saluans diverged about 15,000 years ago, suggesting that the Bajau-unique genetic variants evolved some time after this divergence.

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“'This work provides the first evidence for genetic adaptation in diving human populations and elucidates genetic pathways important in hypoxia tolerance,” Tatum Simonson, who studies the physiology and genetics of high-altitude adaptation at the University of California, San Diego Health Sciences, and was not involved in the work, writes in an email to The Scientist.

"The team’s top hit, a variant adjacent to the BDKRB2 gene, is the only other gene that has previously been found to be associated with a human diving response, but not with spleen size. “We have no idea what it does to change the diving reflex. That is something we would like to explore next,” says Nielsen."

Comment: This is an organ adaptation, not a change in the human species.