A study published recently in the biomedical journal Cell, paints a new picture of human history. Omer Gokcumen, a geneticist at the University at Buffalo, describes early human genetics as “almost as a spider web of interactions, rather than a tree with distinct branches.” This new way of looking at history explains how Neanderthal genes integrated into the human race throughout the years.
Neanderthals have a reputation for being unintelligent, when in fact, they were a refined species. They were skilled hunters and showed artistic abilities. Archaeologists originally found Neanderthal fossils in Europe and Eurasia from 200,000 to 40,000 years ago. The common ancestors of Neanderthals and humans left Africa around 600,000 years ago.
Dr. David Reich, a geneticist at Harvard Medical School was the first to create a Neanderthal genome. A genome shows the DNA present in a cell. The comparisons between the Neanderthal genome and that of humans have suggested that Asians and Europeans have more Neanderthal DNA than Africans do. In 2010, a study using Neanderthal fossil DNA found that humans and Neanderthals only crossed paths 60,000 years ago, after humans left Africa. This reinforced the notion that modern-day Africans have hardly any Neanderthal DNA. However, this year’s study challenged that theory.
This new study suggests that the true first wave of humans departed from Africa 140,000 years before what was initially believed to be the first human migration. Therefore, Neanderthals had interbred with humans before the second wave of humans had even left Africa, leaving both groups with mixed DNA to pass to future generations. Scientists found that a group of humans from Western Eurasia also migrated back to Africa and passed onto their children the Neanderthal genes they had received before returning to the continent. Through this finding, scientists could conclude that Africans actually have a higher percentage of Neanderthal DNA than previously thought.
Joshua Akey, a geneticist at Princeton University, was part of the study published earlier this year. He developed a new method to find Neanderthal DNA in humans, called IBDMix, in order to achieve more accurate results. This method builds on the theory that genes are passed on through generations. The closer one person is with another biologically, the more identical stretches of DNA they will have with the other person. For example, siblings will have many identical segments of DNA, while more distant relatives will share fewer and shorter segments. Dr. Akey created IBDMix with his colleagues to find those identical segments of DNA, which allowed them to compare the DNA of humans today to the DNA from Neanderthal fossils.
One human has about 3 billion base pairs of DNA in their genome. The results of the IBDMix indicate that the average European shares about 51 million base pairs of DNA with Neanderthals while East Asians share 55 million base pairs. Dr. Akey and his team were also surprised to find that Africans have about 17 million common base pairs with Neanderthals, a significantly larger number than they expected.
This study illustrates that humans have migrated over vaster periods of time than we originally believed, and also shared more DNA with others along the way. We are all connected through a web of relationships.
[Sources: The New York Times; Cell; Associated Press]