Neandertal kids were a lot like kids today — at least in how they grew

A Neandertal child whose partial skeleton dates to around 49,000 years ago grew at the same pace as children do today, with a couple of exceptions. Growth of the child’s spine and brain lagged, a new study finds.

It’s unclear, though, whether developmental slowing in those parts of the body applied only to Neandertals or to Stone Age Homo sapiens as well. If so, environmental conditions at the time — which are currently hard to specify — may have reduced the pace of physical development similarly in both Homo species.   

This ancient youngster died at 7.7 years of age, say paleoanthropologist Antonio Rosas of the National Museum of Natural Sciences in Madrid and colleagues. The scientists estimated the child’s age by counting microscopic enamel layers that accumulated daily as a molar tooth formed.

Previous excavations uncovered the child’s remains, as well as fossils of 12 other Neandertals, at a cave site in northwestern Spain called El Sidrόn.

Much — but not all —of the Neandertal child’s skeleton had matured to a point expected for present-day youngsters of the same age, the scientists report in the Sept. 22 Science. But bones at the top and in the middle of the spine had not fully fused, corresponding to a stage of development typical of 4- to 6- year-olds today. Also, the ancient child’s brain was still growing at an age when living humans’ brains have nearly or fully reached adult size. Signs of bone tissue being reshaped on the inner surface of the child’s braincase pointed to ongoing brain expansion. Rosas’ team calculated that the youngster’s brain volume was about 87.5 percent of that expected, on average, for Neandertal adults.

Neandertals’ slightly larger brains relative to people today may have required more energy, and thus more time, to grow, the researchers suggest. And they suspect that the growth of Neandertals’ bigger torsos, and perhaps spinal cords, slowed the extinct species’ backbone development in late childhood.

Rosas’ new study “reinforces what should have been apparent for some time — that Neandertal growth rates and patterns, except for those related to well-known differences in [skeletal shape], rarely differ from modern human variations,” says paleoanthropologist Erik Trinkaus of Washington University in St. Louis.

But researchers need to compare the El Sidrόn child to fossils of H. sapiens youngsters from the same time or later in the Stone Age, Trinkaus adds. Relative to kids today, ancient human youth may display slower growth rates comparable to those of the Neandertal child, he suspects.