The piece of bone was found in the Cova Negra cave site in Spain’s Valencia region and analyzed by a research team led by Mercedes Conde-Valverde of the University of Alcalá in Madrid. The results, published Wednesday in the journal Science Advances, concluded that the fragment likely came from the inner ear of a 6-year-old.

The specimen had evidence of abnormalities, and “the only syndrome that is compatible with the entire set of malformations present in [the fossil] is Down syndrome,” the authors wrote.

Down syndrome — which also occurs in great apes and modern humans — would have presented a range of survival challenges for a child, including “poor sucking strength,” which makes breastfeeding difficult; lack of motor coordination and balance; and impaired cognitive development, the study notes. The child probably experienced severe hearing loss and frequent issues with acute, disabling vertigo and imbalance, it added.

“Because of the demanding lifestyle of Neanderthals, including high levels of mobility, it is difficult to think that the mother of the individual would have been able to provide such care alone and also carry out normal daily activities over a prolonged period of time,” the authors wrote.

It was therefore likely that the mother continuously received help from other members of the social group, they added.

Neanderthals, or Homo neanderthalensis, were a close relative of modern humans that went extinct about 40,000 years ago, leaving traces across Europe and southwest and central Asia. They evolved there as our ancestors — Homo sapiens — were evolving in Africa, likely diverged from a common ancestor at least half a million years ago, according to the Natural History Museum in England.

Implications that Neanderthals could have exhibited care for vulnerable members of their group have been found in previous studies. In 2018, researchers from the University of York reviewed available evidence and concluded that a sample of Neanderthal fossils with healed traumatic injuries suggested that health care was widespread. The care was most likely motivated by investment in the well-being of the members of their social groups, the authors argued.

“This study presents exciting evidence for kinship care on other hominids, where the survival of a little kid with a disability was likely the result of group care, as the pathology … will have deeply affected the ability of the child to survive on its own,” Sofia C. Samper Carro, a senior lecturer in archaeology at the Australian National University specializing in Neanderthal behavior, who was not involved in the study, said in an email.

“For decades, there has been a great interest on discussing what makes us, anatomically modern humans, unique in evolution history. Why did we [survive] when others perished?” Samper Carro said. “One of the proposed factors for our survival against Neanderthal extinction states that our creativity and compassion, caring for others, made us more prone to survive.”

Other scientists have said Neanderthals may have provided care to sick or injured members of their group with the expectation of a reciprocal benefit, rather than out of benevolence. Critics say compassion cannot be authoritatively deduced from remains and requires too many assumptions, the paper in Science Advances acknowledged. Evidence of Neanderthal cannibalism published in 2016 also points to the species’ capacity for brutality.

But the fossil of the child with Down syndrome was “particularly interesting because social care was destined to an immature individual who had no possibility to reciprocate the assistance received,” the authors of that study noted. They added that a caregiving instinct could have a “very ancient origin” in our shared genus.

“Although the link between injuries or pathologies and care for dependents is difficult to demonstrate in ancient bones, I think that the paper … [provides] enough evidence to demonstrate a clear link between child disability and caring commitments from Neanderthals,” Samper Carro said.

“Will we be able to prove unequivocally that Neanderthal had this capacity? Probably not, but studies like the one published are certainly a step in the right direction on demystifying our uniqueness and Neanderthal’s less ‘humane’ behaviour,” she said. “[It] builds on modern research demonstrating how our assumptions about Neanderthal ‘bruteness’ need to be revisited, how the traditional clear cut between ‘simplistic’ Neanderthals and ‘advanced’ Homo sapiens is not longer supported.”