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Skulls of early humans carry telltale signs of inbreeding
Date:
March 18,
2013
Source:
Washington University in St. Louis
Summary:
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 suggests.
............................
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 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 braincase, 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, the Mary
Tileston Hemenway Professor of Anthropology in Arts & 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.
Story
Source:
The above
story is based on materials provided by Washington University in St. Louis. Note: Materials may be edited
for content and length.
Journal
Reference:
- Xiu-Jie Wu, Song Xing, Erik Trinkaus. An Enlarged Parietal Foramen in the Late Archaic Xujiayao 11 Neurocranium from Northern China, and Rare Anomalies among Pleistocene Homo. PLoS ONE, 2013; 8 (3): e59587 DOI: 10.1371/journal.pone.0059587