Analysis of remains from 66 ancient humans reveals that they suffered from an astonishing number of physical deformities, research reveals.

Anthropologist Erik Trinkaus from Washington University in St Louis, US, compiled examination records for two Late Pleistocene infants, six children, four juveniles, six adolescents, 30 prime age adults, and eight older adults, from several archaeological sites around the world.

He discovered that all up they showed evidence of 75 skeletal or dental abnormalities. Based on rates of similar disorders in modern human populations, Trinkaus finds the probability that the total is merely an artefact of comparatively small sample size to be “vanishingly small”.

In a paper published in the journal PNAS, the author says that there is no single factor that could plausibly account for the high number of deformities.

“A substantial number of these abnormalities reflect abnormal or anomalous developmental processes, whether as a result of genetic variants altering developmental processes or as the products of environmental or behavioural stress patterns altering expected developmental patterns,” he writes.

The deformities found included soft bones caused by the blood disorder hypophosphatemia, hydrocephaly, dwarfism, abnormal bone growth, and a wide variety of skull, jaw and dental problems.

Trinkaus is at pains to stress that finding evidence of disfigurements is not itself unexpected in people who died more than 11,000 years ago. The sheer number of them, however, most definitely is.

“Some of these developmental abnormalities are unusual but not exceptional in recent human samples, and thus it would not be surprising to find examples of them in the … human paleontological record,” he writes.

“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.”

He notes that based on their occurrence in modern populations, the chance of finding evidence of the more common abnormalities would be something like 5%, and the chance of finding the rare ones as little as 0.0001%. The chances of finding them in combination, or collectively in evidence in every set of remains to date uncovered and reliably dated, is astronomical.

“The multiplicative cumulative probability of finding the 75 developmental abnormalities is vanishingly small,” he writes.

He acknowledges, however, that 66 sets of remains constitutes in itself the merest fraction of the people who lived and died in the late Pleistocene and that a fuller understanding of the frequency of deformities will not be gained until many more skeletons are discovered.

On the current evidence, however, he advances some possible reasons to account for his findings – after first dismissing the idea of sample bias, on the not unreasonable grounds that there is no evidence that people with deformities received different types of burials which might have increased the chances that they would eventually be discovered.

“The abundance of developmental abnormalities among Pleistocene humans may have been enhanced by the generally high levels of stress evident among these foraging populations,” he writes.

He also tentatively suggests inbreeding – consanguinity, as he terms it – as a factor. Some abnormalities, he notes, are inherited conditions, and the chances of them being expressed would have greatly increased if breeding occurred among closely related individuals.

With the extent of deformities only recently becoming obvious as a result of increasingly sophisticated examination methods, the reasons why our distant ancestors were such a damaged bunch remain unclear.

“Some of these developmental deficiencies are unexceptional from a recent human perspective, although finding multiple cases of them within and across samples and time periods suggests elevated levels of these more common patterns,” writes Trinkaus.

“However, one-quarter of the cases are rare (some extremely so) in extant human samples, and an additional one-fifth of the cases defy proper diagnosis.”