Friday, June 22, 2018

How Did Homo Sapiens Evolve?

Here is a very good summary of our evolving understanding of this question.

How did Homo Sapiens Evolve? - Julia Galway-Witham and Chris Stringer


Over the past 30 years, understanding of Homo sapiens evolution has advanced greatly. Most research has supported the theory that modern humans had originated in Africa by about 200,000 years ago, but the latest findings reveal more complexity than anticipated. They confirm interbreeding between H. sapiens and other hominin species, provide evidence for H. sapiens in Morocco as early as 300,000 years ago, and reveal a seemingly incremental evolution of H. sapiens cranial shape. Although the cumulative evidence still suggests that all modern humans are descended from African H. sapiens populations that replaced local populations of archaic humans, models of modern human origins must now include substantial interactions with those populations before they went extinct. These recent findings illustrate why researchers must remain open to challenging the prevailing theories of modern human origins.

..and on the status of Recent African Origin (RAO) versus Multiregionalism, the two competing theories of modern human origins

The apparently more deeply rooted origin of H. sapiens adds to the problem of how scientists can delineate H. sapiens from other species in an evolutionarily meaningful way and suggests that the species did not evolve as recently as previously envisaged. However, evidence of evolutionary novelty in the fossil record of putative H. sapiens still appears relatively recently in Africa, compared to a multiregional view of human evolution (in which H. sapiens began to evolve at least 1.8 million years ago). Within Africa, it is currently unclear whether the origin of H. sapiens was localized, as in some early RAO formulations, or involved a process similar to multiregional evolution, but operating purely within the continent (5, 13).

With only a few dissenters, the strictest versions of both RAO (which denies interbreeding with other lineages or species) and multiregionalism (which argues for an interbreeding network of one species over the past ~1.8 million years) are now generally regarded as falsified. Instead, two intermediate theories best accommodate the complex interactions between hominin taxa ~40,000 to 100,000 years ago (8, 14): RAO with hybridization (RAOWH) and the assimilation model (AM) (see the figure).

Source: How did Homo Sapiens Evolve? - Julia Galway-Witham and Chris Stringer 2018

Open Access.

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