Genetics is a powerful tool for looking into the past. Two cool examples.
Here's how early humans evaded immunodeficiency viruses
CryoEM reveals structural effect of mutation that made humans, but not apes, immune to SIV
Summary:
The cryoEM structure of a simian immunodeficiency virus protein bound to primate proteins shows how a mutation in early humans allowed our ancestors to escape infection while monkeys and apes did not. ... A mutation in human tetherin disrupted binding, thwarting SIV budding -- until HIV evolved a work-around.
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SIV developed a new trick
Some variants of SIV did eventually find a way around this hurdle, however. At some point, a few SIVs acquired a second protein, Vpu, to do what Nef also did -- wedge itself between proteins to cement connections helpful to the virus. At some point, perhaps a hundred years ago, this strain of SIV moved into humans from chimpanzees, and a slight mutation in Vpu reignited the recycling of tetherin in humans, unleashing what we know today as group M HIV-1, the most virulent form of HIV worldwide.
"There were probably many crossovers into humans that failed, but eventually, some hunter in Africa, perhaps in the course of butchering a chimp, was exposed to the blood, and the virus then acquired an additional mutation, a small step that turned SIV into HIV," Hurley said.
https://www.sciencedaily.com/releases/2019/08/190822141901.htmand
The Paleozoic diet: Why animals eat what they eat
What an animal eats is a fundamental aspect of its biology, but surprisingly, the evolution of diet had not been studied across the animal kingdom until now. Scientists at the University of Arizona report several unexpected findings from taking a deep dive into the evolutionary history of more than one million animal species and going back 800 million years, when the first animals appeared on our planet.
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The survey suggests that across animals, carnivory is most common, including 63% of species. Another 32% are herbivorous, while humans belong to a small minority, just 3%, of omnivorous animals.
The researchers were surprised to find that many of today's carnivorous species trace this diet back all the way to the base of the animal evolutionary tree, more than 800 million years, predating the oldest known fossils that paleontologists have been able to assign to animal origins with certainty.
"We don't see that with herbivory," said Wiens, professor of ecology and evolutionary biology and corresponding author of the study. "Herbivory seems to be much more recent, so in our evolutionary tree, it appears more frequently closer to the tips of the tree."
So if the first animal was a carnivore, what did it prey on?
The authors suggest the answer might lie with protists, including choanoflagellates: tiny, single-celled organisms considered to be the closest living relatives of the animals. Living as plankton in marine and freshwater, choanoflagellates are vaguely reminiscent of miniature versions of the shuttlecock batted back and forth during a game of badminton.
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"The ancient creature that is most closely related to all animals living today might have eaten bacteria and other protists rather than plants," Wiens said.
https://www.sciencedaily.com/releases/2019/08/190822165028.htm