Two Distinct Groups Mated Over Hundreds and Thousands of Years to Give Us the Modern Humans

Human evolution has always been a complex topic to traverse for researchers. Despite many assertions, all the experts have yet to come to a single conclusion regarding this phenomenon. An intriguing theory regarding the creation of modern humans was put forward by a study published in Nature. The new claim challenges the previous assertion that modern humans were born out of a single source.  "There is no single birthplace," said Eleanor Scerri, an evolutionary archaeologist at the Max Planck Institute for Geoanthropology in Germany who did not contribute to the study. "It really puts a nail in the coffin of that idea," stated Smithsonian Magazine.

The study claims that modern humans came into being due to interbreeding amidst two ancestors that belonged to two distinct but closely related evolutionary branches in Africa. Researchers believe that after these genetically different branches had separated, they continued to mix occasionally over many millenniums. Experts associated with the study analyzed modern human genomes of subjects from southern, eastern, and western Africa. The examination also involved samples from 44 individuals of Nama, a southern African group. The Nama are associated with the Khoe-San people, who possess genetic variance from other modern humans. 

The results indicated that modern humans in Africa came from interaction between two or more genetically distinct streams. Researchers claim that around 120,000 to 135,000 years ago modern humans diverged into multiple groups, with one of them eventually becoming the ancestors of Nama. Even before that, there was variance noted in Homo sapiens that suggests they were born out of two or more genetically distinct human populations, that had been participating in interbreeding with each other. It has already been proven in past studies, that the first wave of modern humans came out of Africa around 194,000 years ago, stated Live Science. Hence, the pattern of interbreeding amongst genetically different populations is part of the modern humans' origin story.

Researchers believe that these genetically different populations thrived for so long, at the same time, in Africa, because it was a large continent. Geographical obstacles and social barriers aided these groups to stay separate and develop different characteristics suitable for their environment. As per researchers, some climate changes also encouraged genetic differences. Despite all these factors, researchers don't think the difference was havoc by any means. Hence, experts do not believe that interbreeding took place with significantly different groups like Homo naledi. The finding surprised experts because past examinations have showcased that Homo sapiens lived alongside anatomically different populations.  

The new model asserts that genetic variance in modern humans could be better explained by interbreeding between anatomically similar groups. "When we assume in our computer model that the stem population wasn’t quite as solid, but that parts of it would occasionally branch off and then later merge back together, we get a much better match with the genetic variation found in human populations today," lead author Aaron Ragsdale, a population geneticist at the University of Wisconsin–Madison shared, according to Smithsonian Magazine. Researchers are hopeful that more fossils from the continent will help them to test out their theory. "I am excited to see this discussion evolving — no pun intended — in the near future when more ancient genomes become available," said Omer Gokcumen, an anthropological genomicist at the University at Buffalo in New York, stated Live Science.

The scientific community is ecstatic that more diverse theories regarding the subject of human evolution are coming forth through such studies. "It is exciting that people are starting to model these more complex models and that datasets are becoming available to do this," said Carina Schlebusch, a population geneticist at Uppsala University in Sweden who did not take part in this research.