Thigh Bone DNA Helps Narrow Down When Humans, Neanderthals First Intermingled

Chuck Bednar for redOrbit.com Your Universe Online

Genetic analysis of DNA obtained from a 45,000-year-old modern human thigh bone has allowed researchers to narrow down the time frame in which mating first introduced Neanderthal genes into the human gene pool.

An international team of experts including scientists from the Max Planck Institute for Evolutionary Anthropology, the Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences and Harvard Medical School in Boston report in the latest edition of the journal Nature that interspecies mating first took place between 50,000 and 60,000 years ago.

The thigh bone studied by the genetics team was discovered in Siberia, and Dan Vergano of National Geographic noted that it is the oldest modern human bone discovered that far outside of Africa and the Middle East nearly twice the age of the next oldest, a 24,000-year-old fossil belonging to a boy that died elsewhere in the northern Asian region and whose genome was sequenced in 2013.

Study author and genetics expert Janet Kelso of the Max Planck Institute told Vergano that it was really exciting to have a really high-quality genome sequence of an early modern human that is this old, and that by using DNA from the bone to analyze the mans genetic map, they were able to find that he had roughly 2.3 percent Neanderthal genes. By comparison, modern men and women typically have about 2.1 percent Neanderthal DNA.

After its discovery, the bone reportedly changed hands multiple times before reaching the Max Planck Institute. Once there, the samples remarkably well preserved DNA enabled researchers to extract a genome sequence that Harvard University said was significantly higher in quality than most genome sequences of present-day people generated for analysis of disease risk.

Carbon dating and molecular analysis had revealed the sample belonged to an individual who lived 45,000 years ago and lived on a diet that included plants or plant eaters, as well as fish or other aquatic life forms. The genome sequence further revealed the individual, who has been identified as the Ust-Ishim man, was a modern human and, more specifically, a member of one of the most ancient non-African populations.

The morphology of the bone suggests that it is an early modern human; that is an individual related to populations that are the direct ancestors of people alive today anthropologist Bence Viola, who analyzed the bone, confirmed in a statement Wednesday. This individual is one of the oldest modern humans found outside the Middle East and Africa.

The sequenced genome was also compared to those of present-day humans of over 50 different populations, and it was found that the Ust-Ishim bone originated from a man who is more closely related to present-day non-Africans than to Africans. For that reason, the researchers conclude that he is among the first people to have left Africa and traveled to Eurasia. In addition, his genome was found to be somewhat equally related to both East Asians and to those that lived in Europe during the Stone Age.

The population to which the Ust-Ishim individual belonged may have split from the ancestors of present-day West Eurasian and East Eurasian populations before, or at about the same time, when these two first split from each other, explained Svante Pbo of the Max Planck Institute. It is very satisfying that we now have a good genome not only from Neandertals and Denisovans, but also from a very early modern human.

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Thigh Bone DNA Helps Narrow Down When Humans, Neanderthals First Intermingled