An astonishing number of deformities found in the ancient bones of early humans may have been caused by rampant inbreeding.
75 birth defects, including warped skulls, dwarfism and mutated teeth.
A fifth of the mutations did not match any known modern developmental disorder, researchers said.
Many of the deformities were inherited, and the scientists suspected that they were suspicious.
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75 birth defects, including bowed femurs (left) warped skulls (center), dwarfism and mutated teeth (bottom right)
An archaeologist examines records for two ancient infants, six children, four juveniles, six adolescents, 30 prime age adults, and eight older adults.
The bones, found at sites across Eurasia and the Middle East, mostly date to the past 200,000 years.
In total, the researcher, from Washington University, St. Louis, Missouri found evidence of 75 skeletal or dental abnormalities.
Hypophosphatemia, bowed femurs, and a wide variety of jaw and dental problems.
Scientists said the sheer volume of these deformities was surprising, with two-thirds of the ancient abnormalities occurring in less than one in 100 modern humans.
One quarter of the deformities are rare or extremely rare in modern human populations, while 20 per cent defied proper diagnosis.
Human paleontological record, said Dr. Erik Trinkaus, lead researcher, said: "Some of these developmental abnormalities are unusual but not exceptional
'However, other abnormalities are extremely rare in recent human populations, and the probability of finding such a case in the fossil record would be extraordinary.'
Dr Trinkaus believes that several factors may have contributed to the unusually high number of deformities – including the stress of the hunter gatherer lifestyle.
Researchers have found bone defects in many ancient human bones. Pictured are two misshapen poor bones identified in a skeleton found on a Scottish island in the Hebrides
'The abundance of developmental abnormalities among Pleistocene humans have been published in PNAS.
The anthropologist thus suggested that inbreeding was responsible.
Some abnormalities were inherited and the chances of them appearing so often in small populations would have increased.
This is supported by previous DNA analyzes, which have shown the human populations of this era had a low genetic diversity.
'All the arguments put forward … [inbreeding] seems to be the most likely explanation, 'Hallie Buckley, an archaeologist at the University of Otago at Dunedin, New Zealand, who was involved in the study, told Science Mag.