Human evolution; DNA from ancient hominins (Introduction)

by David Turell , Saturday, October 19, 2019, 19:59 (1652 days ago) @ David Turell
edited by David Turell, Saturday, October 19, 2019, 20:05

New discoveries of DNA from Neanderthals and Denisovans in Malanesians:

https://www.newscientist.com/article/2220381-long-strand-of-dna-from-neanderthals-found...

"Many people have DNA inside them that they inherited from extinct hominins like the Neanderthals – and now we know that in some cases it isn’t just tiny snippets but long stretches.

"Over the past decade, genetic analysis of human DNA has revealed that ancient humans must have interbred many times with other hominins such as Neanderthals. The result is that DNA from these extinct groups can be found in many human populations today.

"In particular, everyone whose primary ancestry was outside Africa carries some Neanderthal DNA, while many people from Asia – especially South-East Asia – have DNA from the mysterious Denisovans. Some of this DNA may have been advantageous for modern humans. (my bold)

***

"The researchers looked at the DNA of people from Melanesia, as the levels of Neanderthal and Denisovan DNA are highest in these populations. They found evidence of much longer chunks of archaic DNA in this population.

"Two large pieces of DNA were found that originate from ancient hominins. One is on chromosome 16 and comes from Denisovans. It contains two duplicated sections. The other is on chromosome 8 and comes from Neanderthals. It includes both a deletion and a duplication.

Duplications are significant because they allow the original gene to be kept, if it is useful, while the copy is free to change and potentially develop a new function. “A duplication is a type of mutation that lets you have your cake and eat it too,” says Eichler.

"Both chunks of DNA show signs of having been selected for by evolution. They seem to have been advantageous and thus become more common in the Melanesian population over the centuries. (my bold)

“'The archaics have contributed to the success of humans that left Africa,” says Eichler. Neanderthals and Denisovans lived in Europe and Asia for hundreds of thousands of years before modern humans emerged from Africa, so they would have evolved adaptations to the different climates, foods and diseases. These useful genes “were kind of test-run in our precursors”, says Eichler. “They’re basically borrowed.”

"However, it is unclear what the advantages have been. “I think the biggest challenge is proving the function,” says Eichler. This will be difficult because the genes are only found in humans, so animal studies will not help, and they have been duplicated and then subtly altered. “You’re talking about a set of genes which are a geneticist’s worst nightmare.'”

Comment: This is another answer to dhw who wonders why God took so long to make H. sapiens. As I've noted before our ancestors developed traits that were passed on as helpful genetics developed in different climates and conditions. My bolds and the last quotes make the exact point. From another article further information:

https://phys.org/news/2019-10-neanderthal-denisovan-dna-early-melanesian.html

"The researchers report that they found instances of inherited CNVs from Denisovans and Neanderthals in modern Melanesian DNA that could be associated with adaptive selection. The researchers suggest the added DNA must have provided some benefit for it to remain in the Melanesian genome for so long. The adaption selections were identified as being associated with immunity, diet, cellular function and metabolism. Their findings suggest that early Melanesian people might have benefited from interbreeding with their early cousins in ways that might have helped them survive in their unique island environments.

"The researchers note that much more work is required to better understand why the inherited CNVs have remained present in the DNA up to the present. The idea that they might have persisted because they were useful has precedent, the researchers note—prior research has shown that Denisovan DNA helped Tibetan people survive in their high-elevation homeland by giving them a means of staving off hypoxia. "