A Japanese study of a chimpanzee mother caring for her disabled infant in the wild has shed light on how humans developed their social behavior.

The first-of-its-kind study by a team of Kyoto University researchers was published Monday in the online edition of Primates, an international journal of primatology.

Born in January 2011 in a chimpanzee group in Tanzania's Mahale Mountains National Park, the female infant was "severely disabled," exhibiting "symptoms resembling Down syndrome," according to a summary of the team's findings.