Skeleton of the Neanderthal boy
© Paleoanthropology Group MNCN-CSIC
Skeleton of the Neanderthal boy recovered from the El Sidrón cave in Asturias, Spain.
The brains of Neanderthal children developed more slowly than those of anatomically modern humans, according to an analysis of a 49,000 year-old juvenile skeleton found in a cave in northwestern Spain.

The analysis was conducted by a team led by palaeobiologist Antonio Rosas of the Museo Nacional de Ciencias Naturales in Madrid, and published in the journal Science.

The scientists found that the Neanderthal child, reliably established to have been 7.7 years old at death, had a brain that was about 87.7% the size of an adult. Human children have a brain 95% of adult size by the same age.

The team also found that some of the child's vertebrae had not fused, while in humans the same bones are fully fused between the ages of four and six.

The skeleton was recovered from the El Sidron cave system in Asturias in Spain, a hotspot for Neanderthal research that has so far produced more than 2,500 remains of seven adults and six juveniles.

Researchers have recovered enough genetic evidence to establish that the group contained three distinct mitochondrial lineages and was likely an extended family. The skeleton used by Rosas and his colleagues has been dubbed "El Sidron J1" and is tentatively thought to be the child of "adult female 4".

Approximately 36% of J1's skeleton has survived 49,000 years underground - enough to allow paleobiologists to make some firm and detailed observations about age and stature, but not about gender. However, the team writes that "evaluation of canine size and bone robusticity strongly suggests that it was male".

The skeleton's dentition comprised a mixture of permanent and milk teeth, allowing a confident conclusion that the child was aged between seven-and-a-half and eight at the time of death.

Close inspection of the skull remnants showed evidence of bone resorption - the process by which cells called osteoclasts break down bone tissue and release calcium into the bloodstream. This indicates that the brain was still growing.

The authors take care to point out that although J1's brain was smaller - relative to adult scale - than an equivalently aged modern human the evidence says nothing about intelligence, either at that age or at full maturity.

Neanderthals had larger cranial capacity than Homo sapiens, and different body shapes. Brain growth is a very energy intensive process, and the development pattern, the researchers conclude, might simply reflect different juvenile development trade-offs "rather than defining a fundamental difference in the overall pace of growth in this species of Homo".