Fossils Found in China Show Evidence of Inbreeding among Early Humans

A new study based on the analysis of an approximately 100,000-year-old skull from Xujiayao in the Nihewan Basin of northern China has found that inbreeding was common among our ancestors.

The study was conducted by researchers from Chinese Academy of Sciences and Washington University in St. Louis.

The skull was found to have a rare congenital disorder, which researchers say might have been a result of inbreeding.

Enlarged parietal foramen (EPF) or "hole in the skull" is now found in people diagnosed with a rare mutation in the homeobox genes ALX4 on chromosome 11 and MSX2 on chromosome 5, according to a news release. Today, just one in every 25,000 babies has this kind of mutation which prevents skull fragments from closing completely.

Previous research has found that the skulls of Pleistocene humans had high rates of genetic abnormalities like the one documented in the present study. Researchers said that there are many such fossil skulls belonging to early Homo erectus, to the people living in the end of Stone Age having such genetic mutation that are rare in modern humans.

"The probability of finding one of these abnormalities in the small available sample of human fossils is very low, and the cumulative probability of finding so many is exceedingly small," said Erik Trinkaus, professor of Anthropology in Arts & Sciences at Washington University in St. Louis and co-author of the study.

Although the skull, known as Xujiayao 11, had EPF, researchers found that cognitive deficits arising from this genetic mutation were minor.  

"The presence of the Xujiayao and other Pleistocene human abnormalities therefore suggests unusual population dynamics, most likely from high levels of inbreeding and local population instability," Trinkaus added.

The study is published in the journal PLOS One.