Recovered skull fragments of an early human ancestor from 100,00 years ago discovered at Xujiayao in northern China could indicate that inbreeding might have been more common among our ancestors than previously believed.
That is because the skull shows tell-tale signs of a rare congenital defect called an enlarged parietal foramen (EPF), which is caused when genetic mutations prevent the closer of small holes in the braincase, something that usually occurs in the first five months of fetal development. It occurs in 1 out of every 25,000 births.
Traces of EPF and other genetic abnormalities are seen often in early humans, from Homo erectus clear through modern humans. Probability dictates that rare abnormalities like EPF should not be common among the small samples of fossils so far discovered. The fact that these deformations are relatively common in the fossil records suggest that ancient inbreeding occurred regularly. This was likely due to humans living in small, isolated groups.
These new insights into ancient population dynamics could affect our understanding of human evolution, as some current models assume a relatively large, stable population.