Human evolution: lots of interbreeding (Introduction)

by David Turell , Tuesday, October 15, 2024, 00:08 (3 days ago) @ David Turell

Human DNA is a mixture, not pure:

https://www.scientificamerican.com/article/human-origins-look-ever-more-tangled-with-ge...

"Only 200,000 years ago, our ancestors lived on a planet teeming with varied human relatives: Neandertals lived in Europe and the Middle East. Denisovans, known today only from bone fragments, teeth and DNA, dwelled across Asia and perhaps even in the Pacific. “Hobbits,” or Homo floresiensis, a diminutive species, lived in Indonesia, as another short-statured species, called Homo luzonensis, did in the Philippines. Even Homo erectus, the grandparent of early human species, was still running around as recently as 112,000 years ago.

"Now they are all gone. Except in our genes. Denisovans interbred with Neandertals, and both mated with modern humans. Genes from “an unknown hominin in Africa” also mark modern humans’ genomes. The initial discovery of these admixtures, starting in 2010, shook up the once-conventional “Out of Africa” picture of human origins, which saw a small, singular group of human ancestors developing language and then replacing all others worldwide within the last 100,000 years.

"Instead, the emerging picture of our origins is less of a family tree, and more of a tangled shrub, one whose winding branches wove distinct human groups together into today’s broader human population. People today largely derive from interbreeding between modern-looking humans in Africa and the disparate human populations littering the wider world. Those African expatriates themselves first arose from scattered, intermittently admixtured populations found across that continent.

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"...with evidence hinting that Homo sapiens lived in Greece 210,000 years ago, then ceded Europe to Neandertals. Genetic studies suggest this gene-swapping peaked twice, at about 200,000 years ago and again 50,000 years ago. Even some of the bacteria in our mouths, ponder that, appear to have a Neandertal origin. Because of that early mixing, Neandertals themselves averaged 2.5 to 3.7 percent Homo sapiens DNA, a contribution that confused the family tree later.

***

"A similar picture of shuffled genes and small populations is shaping up for Denisovans and other archaic human species. All this genetic shuffling leaves humanity itself looking like a bit of a mess. A July 2021 analysis for example found that “only 1.5 to 7 [percent] of the modern human genome is uniquely human.”

"That’s not a lot. In a review of humanity’s scattered genetic history, scientists, including Chris Stringer of the Natural History Museum in London, once a champion of a strict Out of Africa view of human origins, looked over the patchwork of human and archaic fossils and genes. Stringer and colleagues concluded in Nature in 2021 that “no specific point in time can currently be identified at which modern human ancestry was confined to a limited birthplace.”

"Our origin therefore does not appear to be a particularly tidy one, but a complex one that involved a lot of mating across time and space. We weren’t so much conquerors as wanderers, and potential in-laws, in our new neighborhoods. Something to consider the next time you hear someone going on about their family history, or how other people are unwanted outsiders."

Comment: Not a surprising conclusion. Each sob-group contributed useful genetic attributes such as the well-known immunity contribution from the Neanderthals. A designer might have done this to make His work simpler, with each group supplying useful attributes from their environmental experiences.