Human evolution; Africa has 90% of the evolution (Introduction)

by David Turell , Monday, September 23, 2019, 20:58 (1678 days ago) @ David Turell

A theoretical essay:

https://phys.org/news/2019-09-modern-humans-species.html

"...a group of researchers argues that our evolutionary past must be understood as the outcome of dynamic changes in connectivity, or gene flow, between early humans scattered across Africa. Viewing past human populations as a succession of discrete branches on an evolutionary tree may be misleading, they said, because it reduces the human story to a series of "splitting times" which may be illusory.

"According to archaeologist Dr. Eleanor Scerri and geneticists Dr. Lounès Chikhi and Professor Mark Thomas, the quest for a single original location for modern humans is a wild goose chase. "People like us began to appear sometime between 500,000 and 300,000 years ago," says Dr. Scerri, group leader of the Pan-African Evolution Research Group at the Max Planck Institute for the Science of Human History and lead author of the study. "That is something in the order of 8000 generations, a long time for early people to move around and explore a big space. Their movements, patterns of mixing and genetic exchanges, are what gave rise to us."

"'The genetics of contemporary humans are very clear. The greatest genetic diversity is found in Africans," explains Prof. Thomas of University College London. "The old theory that we descend from regional populations spread across the Old World over the last million years or so is not supported by genetics data. Sure, non-Africans today have some ancestry from Neanderthals, and some have appreciable ancestry from the recently discovered Denisovans. And maybe other, as yet undiscovered ancient hominin groups also interbred with us, Homo sapiens. But none of this changes the fact that more than 90 percent of the ancestry of everybody in the world lies in Africa over the last 100,000 years."

***

"'Instead of a series of population splits branching off an ancestral tree, changes in connectivity between different populations over time seem a more reasonable assumption, and appear to explain several patterns of genomic diversity not explained by current alternative models. Metapopulations are the kind of model you'd expect if people were moving around and mixing over long periods and wide geographic areas. We cannot objectively identify this geographic area today from genetic data alone, but data from other disciplines suggest that the African continent represents the most likely geographical scale."

"The scientists argue that this view is not only better supported by the fossil, genetic and archaeological evidence, it also better explains the paleoanthropological record beyond Africa.

"'We see physically diverse early human fossils from across Africa, some very old genetic lineages and a pan-African shift in technology and material culture that reflects advanced cognition, including new technical and social innovations, across the continent. In other words, what you'd expect from a dynamic interconnected patchwork of populations that were at times more or less isolated from each other," says Dr. Scerri. "This would also help to explain the increasing evidence for unexpected populations, including in areas outside Africa such as the Hobbits on Flores," she adds.

"'A metapopulation model helps us to find a way to acknowledge the paleontological, archaeological and genetic evidence for a recent African origin with limited gene flow from non-African metapopulations, such as Neanderthals, without falling into overly polemic and restrictive debates," adds Dr. Scerri. (my bold)

***

"'If we look at the available data through the lens of changes in connectivity, the record starts to make a lot more sense. We need such flexibility to be able to make sense of the past, or we get lost in a malaise of ever-increasing named species, failed trajectories and population trees that never existed," says Prof. Thomas. "Science always favors the simpler explanation and it is becoming increasingly difficult to stick to old narratives when they have to become over-complicated in order to stay relevant," he adds.

"'Our African origins cannot be denied, but we definitely don't yet have the resolution to include or exclude different bits of evidence simply because they don't fit with a particular view. We need better reasons than that," says Dr. Scerri."

Comment: the authors point is very important. Perhaps most of human evolution occurred in African populations and the outside fossils represent simply migration with local changes. This fits my concept of a purposeful God who didn't create scattered populations for no good reason, as suggested by my bolded statement in the article.