Evidence of Inbreeding Found in Early Humans Skulls

Evidence that early humans may have practiced inbreeding has been found in fossils, researchers announced Monday according to an article published on the journal PLOS ONE.

In Xujiayao, a site in the Nihewan Basin of northern China, scientists uncovered a 100-year-old human skull that showed signs of physical malformations. The researchers determined that the skull had a now-rare congenital deformity that probably arose through inbreeding.

Baptized as Xujiayao, the fossil belonged to a 11-year, and it constitutes just one of many examples of ancient human remains that shows rare or unknown congenital abnormalities, according to the researchers.

"These populations were probably relatively isolated, very small and, as a consequence, fairly inbred," study leader Erik Trinkhaus, an anthropologist at Washington University in St. Louis, told LiveScience.

According to UPI.com, the skull has a hole at its top, a disorder known as an "enlarged parietal foramen," which matches a modern human condition of the same name caused by a rare genetic mutation. The genetic abnormalities obstruct bone formation by preventing small holes in the prenatal braincase from closing, a process that normally occurs within the first five months of the fetus' development. Today, these mutations are rare, occurring in only about one of every 25,000 human births.

The fact that the individual appeared to have lived until his middle age, shows that the abnormality was not lethal. The skull deformity can sometimes lead to cognitive deficits, but the age of the individual suggests any deficits probably would have been minor, Trinkhaus said.

The present findings corroborated with the data known about our distant past. More often than not, human skulls from the Pleistocene – the period between 2.6 million and 12,000 years ago – show an unusually high occurrence of genetic abnormalities like this skull-hole deformity, the scientists have found. Scientists have seen these abnormalities in fossils from the time of early Homo erectus to the end of the early Stone Age.

“Such a high frequency of genetic abnormalities in the fossil record reinforces the idea that during much of this period of human evolution, human populations were very small and, consequently, inbred may have been very likely,” Trinkhaus said.