Convoluted human evolution: mixing subtypes (Introduction)

by David Turell @, Monday, February 08, 2016, 15:18 (1291 days ago) @ David Turell

A anthropologist discusses what DNA genetic studies tell us about the intermixing and how current humans picked up straits from different sub-species:

"Where once we saw each branch in isolation, DNA evidence now reveals a network of connections. From an African origin more than 1.8 million years ago, human ancestors flowed into different populations, following separate paths for hundreds of thousands of years, yet still coming together to mix their genes.


"Even ancient genomes have ghosts within them. The Denisovan genome bears the traces of ancient mixture, not only from Neanderthals but with another even more divergent group - some speculate it might have been Homo erectus. Everywhere geneticists look, they see populations more different than any living people, mixing with each other in small fractions. It is no evolutionary tree. Our evolutionary history is like a braided stream.


"In the 1970s, geneticists noticed that humans are surprisingly inbred for a worldwide species. Other great apes - the chimpanzees, gorillas, and orangutans - each have much more variation, so much that today's primatologists recognise two species of orangutans, and up to four species of chimpanzees and gorillas. These apes have deep histories, with populations separated for hundreds of thousands of years. By contrast, humans throughout the world look like refugees from a single small part of Africa.


"When Neanderthals, Denisovans and ghost lineages, both inside and outside Africa, walked the Earth, their populations were each quite inbred, but collectively they were diverse, more like gorillas or chimpanzees than today's humans. Across the past 200,000 years, these separate streams were swallowed up by the growth of one African branch of humanity. Humans spread through the world like a broad river delta, carrying slightly different fractions of the flow of ancient streams.

"We don't yet know what triggered the success of these ancient Africans. But we can see some ways that they benefited from mixing with distant populations. As they mixed, they picked up biological solutions first innovated and road-tested by distant populations. Already, we have found Neanderthal or Denisovan genes contribute to immunity, metabolism and proteins expressed in hair and skin. A gene derived from Denisovans has helped people adapt to the low-oxygen environment of the Tibetan plateau. (my bold)


"The braided stream of human evolution matches with what we are seeing in other mammals. As geneticists have sampled more and more populations of wild animals, they are finding what has been known for our domesticated plants and animals for a long time: hybridisation and introgression of genes among species and distant populations is ubiquitous in the natural world."

Comment: It appears that the mixing of the different types of hominins/humans contributed much to present-day humans success in surviving the challenges of nature. Note the bold above. My conclusion is the "ancient Africans" can be viewed as a purposeful result.

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