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A New Perspective on Human Evolution: Multiple African Populations Gave Rise to Homo Sapiens

A groundbreaking study published in the journal Nature on May 17, 2023, challenges previous theories on human evolution by suggesting that Homo sapiens arose from multiple closely related populations across Africa. This new model has significant implications for the interpretation of the fossil record.

Using genetic data from present-day African populations, including 44 newly sequenced genomes from the Nama group of southern Africa, researchers found that the earliest detectable split in early human populations occurred between 120,000 and 135,000 years ago, after prolonged periods of genetic intermixing. The study also discovered that contributions from archaic hominins were unlikely to have significantly affected Homo sapiens' evolution.

The origin of Homo sapiens has been a topic of debate among scientists, with Africa widely accepted as the birthplace of our species. However, uncertainty surrounded specific models of divergence and migration. This study employed linkage disequilibrium and diversity-based statistics for demographic inference, allowing researchers to evaluate a wide range of alternative models.

The 44 new genomes from the Nama people provided valuable data for the study, revealing weakly structured stem models that explained patterns of polymorphism previously attributed to contributions from archaic hominins in Africa. Consequently, fossil remains from coexisting ancestral populations should be genetically and morphologically similar. The study also found that only 1-4% of genetic differentiation among contemporary human populations could be attributed to genetic drift between stem populations, making it difficult to reconcile the tree-like model of recent population divergence from a single ancestral population in Africa with the fossil and archaeological records.

Researchers used geographically and genetically diverse populations across Africa to infer demographic models, confirming the inadequacy of tree-like models and allowing for the evaluation of alternative models. Demographic histories were inferred from 4x-8x whole-genome sequencing data for four diverse African populations.

The earliest divergence among contemporary human populations differentiates the southern African Nama population from other African groups at 110-135 thousand years ago. The study also found high gene flow between eastern and western Africa, as well as back-to-Africa gene flow at the beginning of the Holocene epoch, primarily affecting ancestors of Ethiopian agricultural populations.

Models allowing for migration between stem populations outperformed those without migration between stems, providing further evidence for the new model of human evolution. The study also suggests that population structure extends back to more than 1 million years ago.

In conclusion, this groundbreaking research offers a new perspective on human evolution, suggesting that Homo sapiens arose from multiple closely related populations across Africa. The findings challenge previous theories and have significant implications for the interpretation of the fossil record. As our understanding of human evolution continues to grow, it becomes increasingly clear that the story of our species is a complex and fascinating one, with many more discoveries yet to be made.