According to a new theory of human evolution, numerous closely related groups gave rise to Homo sapiens
A new model for human evolution asserts that modern Homo sapiens stemmed from multiple genetically diverse populations across Africa rather than a single ancestral population. This conclusion was reached after researchers analyzed genetic data from present-day African populations, including 44 newly sequenced genomes from the Nama group of southern Africa.
The earliest discernible separation between Homo sapiens and other different species occurred between 120,000 and 135,000 years ago, following extended periods of genetic mixing, according to a recent study published in Nature, which contradicts long-held beliefs.
Researchers have discovered a new model of human evolution, disproving earlier theories that claim that a single African population gave rise to all humans. They did this by analyzing the genetic makeup of current populations in Africa and comparing it to fossil evidence of early Homo sapiens populations there. On May 17, the journal Nature published the latest study.
Although it is well known that Homo sapiens began in Africa, Brenna Henn, professor of anthropology at the Genome Center at UC Davis, and the study's corresponding author, said that it is unclear how human evolution branches diverged and how humans moved across the continent.
"This uncertainty is due to limited fossil and ancient genomic data, as well as the fact that the fossil record does not always align with expectations from models built using modern DNA," the author stated. "This new study alters the theory of species origins."
View of the village of Kuboes, on the border of South Africa and Namibia. DNA samples were collected from Nama individuals who have historically lived in the region. Credit: Brenna Henn/UC Davis
Henn and Simon Gravel of McGill University co-led research that used population genome data from southern, eastern, and western Africa to examine various opposing theories of evolution and migration across Africa that have been put forth in the paleoanthropological and genetics literature.
The 44 modern Nama people from southern Africa, an Indigenous population noted for having very high levels of genetic variation in comparison to other modern groups, were included in the authors' study along with newly sequenced genomes. Between 2012 and 2015, researchers collected saliva samples from contemporary people going about their daily lives in their communities in order to generate genetic data.
The model predicts that after two or more slightly genetically distinct Homo populations had been mixing for hundreds of thousands of years, the earliest population split among early humans that is discernible in modern populations took place 120,000 to 135,000 years ago. People continued to move between the stem populations after the population split, resulting in a weakly structured stem. The authors argue that this provides a more comprehensive account of genetic variation within and between human populations than earlier theories.
Henn stated of the study, "We are presenting something that people have never even tested before." This makes major progress in anthropological science.
Nama woman standing in the doorway to her home in Kuboes, South Africa, a UNESCO World Heritage Site. Credit: Justin Myrick-Tarrant/with permission
Tim Weaver, co-author and professor of anthropology at the University of California, Davis, noted that earlier, more complex models had suggested contributions from archaic hominins, but that this model shows otherwise. He contributed comparative research for the study and is an authority on the appearance of early human fossils.
According to the scientists' predictions, variation in the stem populations will account for 1-4% of genetic difference between modern human populations. The application of this paradigm could have significant ramifications for how the fossil record is interpreted. These numerous lineages were likely morphologically similar due to migration between them, which means morphologically different hominid fossils (such Homo naledi) are unlikely to represent branches that helped to evolve Homo sapiens, according to the authors.
