Scientists report in a new study based on looking at genetically deformed 100,000-year old fossil skulls that human inbreeding may have been common in prehistory. Buried for 100,000 years at Xujiayao in the Nihewan Basin of northern China, the recovered skull pieces of an early human exhibit a now-rare congenital deformation that indicates inbreeding might well have been common among our ancestors, new research from the Chinese Academy of Sciences and Washington University in St. Louis suggests.
The question remains was it inbreeding or malnutrition? Scientists report that the cause points to inbreeding and population instability. There weren't many humans near one another 100,000 years ago in northern China, long before the last ice age, according to the March 19, 2013 news article, "Early human skulls hint at inbreeding | Health24."
The skull, known as Xujiayao 11, has an unusual perforation through the top of the brain case -- an enlarged parietal foramen (EPF) or "hole in the skull" -- that is consistent with modern humans diagnosed with a rare genetic mutation in the homeobox genes ALX4 on chromosome 11 and MSX2 on chromosome 5.
These specific genetic mutations interfere with bone formation and prevent the closure of small holes in the back of the prenatal brain case, a process that is normally completed within the first five months of fetal development. It occurs in about one out of every 25,000 modern human births.
Although this genetic abnormality is sometimes associated with cognitive deficits, the older adult age of Xujiayao 11 suggests that any such deficits in this individual were minor. Traces of genetic abnormalities, such as EPF, are seen unusually often in the skulls of Pleistocene humans, from early Homo erectus to the end of the Paleolithic.
"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," suggests study co-author Erik Trinkaus, according to the March 18, 2013 news release, "Skulls of early humans carry telltale signs of inbreeding, study suggests." Trinkaus is the Mary Tileston Hemenway Professor of Anthropology in Arts and Sciences at Washington University in St. Louis.
"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." It therefore provides a background for understanding populational and cultural dynamics through much of human evolution. Also see the studies, "Men’s Preference for Women’s Facial Features: Testing Homogamy and the Paternity Uncertainty Hypothesis," and "Genetic Structure of Europeans: A View from the North–East."
Published March 18, 2013 in the journal PLoS ONE, the study is co-authored by Xiu-Jie Wu and Song Xing of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing. Its findings are based on the analysis of the fossilized partial skull of an adult late archaic human from the Xujiayao site, in the Nihewan Basin of northern China.
For further information, also check out a March 19, 2013 Fox News article, "Inbreeding common in early humans, deformed skull suggests" or the Science Daily March 19, 2013 article, "Skulls of early humans carry telltale signs of inbreeding."
As for scientific articles on inbreeding in history, check out, "The Role of Inbreeding in the Extinction of a European Royal Dynasty," and "Unexpected Relationships and Inbreeding in HapMap Phase III Populations." And if you're interested in more archaeology current explorations, check out the YouTube video on Genghis Khan's tomb search by Landrover USA, "Seeking Genghis Khan's Great Secret by landroverusa."
Local studies near Sacramento of prehistoric humans and their health issues
In the Sacramento region and the California coastal area, the University of California, Davis also researches prehistoric humans, for example, what in the environment may have led to their health decline in the study, "Could the Health Decline of Prehistoric California Indians be related to exposure to Polycyclic Aromatic Hydrocarbons (PAHs) from Natural Bitumen?" The negative health effects of polycyclic aromatic hydrocarbons (PAHs) are well established for modern human populations but have so far not been studied in prehistoric contexts.
PAHs are the main component of fossil bitumen, a naturally occurring material used by past societies such as the Chumash Indians in California as an adhesive, as a waterproofing agent, and for medicinal purposes. What led to the health decline locally of prehistoric peoples before the Central Valley's problem with air pollution from modern industry?
The rich archaeological and ethnohistoric record of the prehistoric coastal Chumash suggests that they were exposed to multiple uptake pathways of bituminous PAHs, including direct contact, fume inhalation, and oral uptake from contaminated water and seafood. You may wish to also check out that study of local prehistoric humans and their health issues from the environment as it was locally thousands of years ago.