Human evolution: how we lost our tails (Introduction)

by David Turell , Thursday, February 29, 2024, 01:25 (279 days ago) @ David Turell

A genetic transposon:

https://www.sciencenews.org/article/genetic-parasite-humans-apes-tail-loss-evolution

"Around 25 million years ago, this parasite, a small stretch of repetitive DNA called an Alu element, ended up in a gene important for tail development, researchers report in the Feb. 29 Nature. The single insertion altered the gene Tbxt in a way that seems to have sparked one of the defining differences between monkeys and apes: Monkeys have tails, apes don’t.

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"Alu elements are part of a group of genetic parasites known as transposons or jumping genes that can hop across genetic instruction books, inserting themselves into their hosts’ DNA (SN: 5/16/17). Sometimes, when the gene slips itself into a piece of DNA that is passed down to offspring, these insertions become permanent parts of our genetic code.

"Transposons, including more than 1 million Alu elements, are found throughout our genome, says geneticist and systems biologist Bo Xia of the Broad Institute in Cambridge, Mass. Researchers once thought of transposons as genetic garbage, but some have central roles in evolution. Without transposons, the placenta, immune system and insulation around nerve fibers may not exist.

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"The team found that in monkeys, including baboons and rhesus macaques, the Tbxt gene was missing a chunk of DNA that’s found in humans, chimpanzees and other apes. It was a “eureka moment,” Boeke says. The insertion may have appeared around the time apes diverged from African and Asian monkeys, around 25 million years ago.

"But the missing chunk was in a part of the gene called an intron, a bit of genetic material that isn’t made into proteins. “So why would that even matter?” he asks. A close look at the gene’s structure provided a plausible explanation: The missing bit tweaked Tbxt so that the gene makes a different form of the protein in apes than in monkeys.

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"The new findings do begin to unravel how apes lost their tails, says Gabrielle Russo, a biological anthropologist at Stony Brook University in New York. But why it happened, she says, is a much harder question to answer. Research from the early 1900s linked tail loss to muscle changes that helped human bodies move upright, but shifts in posture, as well as learning to walk on two feet, didn’t happen until millions of years later (SN: 9/15/21; SN: 4/14/21). So, it’s unlikely the new findings will shed light on these human traits, Russo says."

Comment: apes don't have upright posture, tails or not. We are exclusively very different. We are not naked apes, as we were previously called!!!