Neandertal Skeleton Reveals Growth Pattern of Our Extinct Cousins

A new analysis of a well-preserved skeleton of a Neandertal child reveals that the ancient human species may have had an extended period of brain growth compared to modern humans. The results are published in the September 22 issue of Science.

Skeleton of Neandertal boy El Sidrón J1, recovered from the El Sidrón cave (Asturias, Spain) | Paleoanthropology Group MNCN-CSIC

"Apart from the innate curiosity we humans have, the analysis of Neandertals is fundamental to answer a basic question: what makes us humans?" explained Antonio Rosas of the National Museum of Natural History of Spain, an author of the study. "Neandertals are our closest relatives and through comparative analyses we can isolate how specific human traits have evolved."

Scientists are particularly curious about differences in brain size, since adult Neandertals tend to have a cranial capacity of about 1,500 cubic centimeters and modern day humans have a cranial capacity of about 1,350 cubic centimeters. The development of a large brain requires significant energy intake, and in modern humans this high cost of brain growth during infancy and childhood seems to be balanced out by a slower growth rate in the rest of the body, Rosas and his colleagues said.

It is unclear if Neandertals grew their large brains using a similar strategy, the researchers said. Some scientists have proposed that the species had a bigger brain because it experienced a faster rate of early postnatal growth, but others have proposed a longer growth period instead.

To gain a better understanding of Neandertal growth, Antonio Rosas and colleagues described the skeleton of a Neandertal child that lived about 49,000 years ago. The skeleton was found with the remains of more than a dozen other Neandertals in a limestone cave, El Sidrón, in Spain. The specimen, dubbed El Sidrón J1, exhibits an exceptionally well-preserved mix of baby and adult teeth, which is helpful for pinpointing the age of the child. Using markings on the teeth, the team estimates that the child died at 7.7 years of age.

Based on his team's analysis, Rosas said that Neandertals had an overall growth pattern quite similar to ours. "However, some specific anatomical systems had a more extended period of growth; in particular, parts of the vertebral column and quite possibly also in the brain."

For example, the team found that some vertebrae had still not fused (a sign of skeletal maturation) in the 7-year-old Neandertal, yet these same vertebrae tend to fuse in modern day humans around the ages of 4 to 6. As well, the brain of El Sidrón J1 was roughly 87.5% of the size of an average adult Neandertal brain upon death, whereas modern humans tend to have on average 95% of adult brain weight by that same age.

The authors suggest that the unique pattern of vertebral maturation and longer period of brain growth might reflect the larger and broader body form typical of Neandertals.

The mysteries surrounding our extinct cousins will continue to be solved piece-by-piece as more data and skeletons are analyzed. "We have already [begun] the analysis of other immature remains coming from the El Sidrón site," said Rosas, noting that his team has the remains of three adolescent individuals. "This is very exciting as the study of the adolescence period is vital in human development."

[Credit for associated image: (Left to right) Antonio García-Tabernero, Antonio Rosas and Luis Ríos beside the Neanderthal child’s skeleton/ Andrés Díaz-CSIC Communication]