Anthropologist Erik Trinkaus has discovered an unusually large number of physical deformities among the earliest humans.

According to a new study, the multitude of deformities could be explained by inbreeding among early human populations.

Trinkaus, a professor at Washington University in St. Louis, identified evidence of 75 skeletal or dental defects among 66 early humans, including bowed arm and leg bones, as well as skull, jaw and dental deformities. Trinkaus also found evidence of blood and brain disorders, as well as dwarfism.

The fossil remains hail from the Pleistocene, the period extending from 2.6 million years ago to approximately 11,700 years ago. Most of the fossils are 200,000 years old.

Many of the abnormalities likely had little impact on the lives of early humans, but some would have been debilitating.

Trinkaus exhaustively surveyed the fossil record, locating instances of physical deformity. He found evidence of abnormalities among human remains recovered from across the globe, including China, the Czech Republic, Italy and Israel.

The odds of discovering such a large number of abnormalities among such a small sample size are extremely small, which suggests the anomaly is not a coincidence.

According to Trinkaus, one possible cause of the "abundance of developmental anomalies" is inbreeding, or consanguinity — breeding among blood relatives.

Hallie Buckley, a bioarchaeologist at the University of Otago in New Zealand, told Science Magazine earlier studies of Pleistocene human DNA suggests genetic diversity was limited among early human populations.

"Of all the arguments put forward … this seems the most likely explanation," Buckley said.

However, Trinkaus thinks a variety of factors played a role.

One of the factors was likely stress. The Pleistocene was a harsh place.

"The abundance of developmental abnormalities among Pleistocene humans may have been enhanced by the generally high levels of stress evident among these foraging populations," Trinkaus wrote in a paper on the discovery, published this week in the journal PNAS.