Wednesday, December 20, 2023

Why Chimpanzees are more diverse than Humans despite sharing 98.8% genetic similarity to humans.

 "The researchers also contrasted the levels of genetic variation between the chimpanzee groups with that seen in humans from different populations. Surprisingly, even though all the chimpanzees live in relatively close proximity, chimpanzees from different populations were substantially more different genetically than humans living on different continents. That is despite the fact that the habitats of two of the groups are separated only by a river. Professor Peter Donnelly, director of the Wellcome Trust Centre for Human Genetics at Oxford University and a senior author on the study, noted: 'Relatively small numbers of humans left Africa 50,000-100,000 years ago. All non-African populations descended from them, and are reasonably similar genetically.'

'That chimpanzees from habitats in the same country, separated only by a river, are more distinct than humans from different continents is really interesting. It speaks to the great genetic similarities between human populations, and to much more stability...."
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"If human and chimp DNA is 98.8 percent the same, why are we so different? Numbers tell part of the story. Each human cell contains roughly three billion base pairs, or bits of information. Just 1.2 percent of that equals about 35 million differences. Some of these have a big impact, others don't. And even two identical stretches of DNA can work differently--they can be "turned on" in different amounts, in different places or at different times."
"The same genes are expressed in the same brain regions in human, chimp and gorilla, but in different amounts. Thousands of differences like these affect brain development and function, and help explain why the human brain is larger and smarter."
"chimps don't get infected by the malaria parasite Plasmodium falciparum, which a mosquito can transmit through its bite into human blood. A small DNA difference makes human red blood cells vulnerable to this parasite, while chimp blood cells are resistant."
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"However, chimpanzees are recognized as a discontinuous species, with four subspecies separated by historical geographic barriers.....overrepresentation of site pairs within P. t. verus, which is known to have the lowest diversity of all subspecies15,33, resulting in a very low intercept. Fitting G ~ D regressions within each subspecies pair, instead, did not reveal clear evidence of abrupt discontinuities across the chimpanzee range (Fig. 2c, d), but rather highlighted ‘locally’ different patterns. "
"...relative diversity rates (q; pairwise within-deme genetic dissimilarity between individuals)"
"our observations of high effective migration rates in P. t. verus may simply be a consequence of the overall paucity of diversity in this subspecies."
"Genetic diversity is more pronounced within population groups than between them, with only a few gene differences accounting for the wide variations seen in eye, skin and hair color across humanity. So animals all about the same size and color and showing few behavioral differences must be even more genetically identical, right? Wrong, says Molly Przeworski, assistant professor of human genetics at the University of Chicago. Her team looked at the DNA of the three designated populations of chimpanzees in Africa -- the eastern, western and central populations, designated by some researchers as sub-species of the chimpanzee. They found that a western chimpanzee has more differences, genetically, from an eastern chimp than any one human being has from another. Gene study shows chimps more diverse than humans"

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