Neanderthal infants were enormous compared with modern humans

Neanderthal babies may have physically dwarfed their Homo sapiens counterparts, according to a new study that examined an infant skeleton of one of our ancient hominin relatives.

“We cannot say how advanced Neanderthal babies were in their behaviour,” says Ella Been at Ono Academic College in Israel. “We do not know whether they started walking at a different time than modern human babies do.” But, she says, they were big and “not necessarily chubby”.

Been and her colleagues conducted a detailed anatomical analysis of the almost-complete skeleton of a Neanderthal baby who lived in what is now Israel sometime between 51,000 and 56,000 years ago.

The infant, known as Amud 7, was discovered in a cave 4 kilometres from the western shore of the Sea of Galilee in Israel in 1992. Their sex cannot be determined. Amud 7 is one of only a handful of young Neanderthals that have ever been recorded.

Neanderthals were the dominant species of hominin throughout Eurasia for several hundred thousand years until climate change and competition with modern humans saw them become extinct around 40,000 years ago.

Based on the stage of the eruption of the baby’s teeth and microscopic scans of the teeth’s internal structure, Amud 7 was probably about 6 months old when they died, says Been.

But in terms of bone length and brain development, Amud 7 is more comparable to a modern human aged between 12 and 14 months old. In other words, the infant seems to have a young dental age and a much older skeletal age.

Been says when the researchers compared these findings from Amud 7 with those from two other Neanderthal infants, a 2-year-old named Dederiyeh 1 from Syria and a 3-year-old found at Roc de Marsal in France, they saw the same trend.

“Seeing the same pattern in three different Neanderthal infants shows that this is not accidental,” says Been.

Trying to fit Amud 7 and the other Neanderthal youngsters’ developmental markers onto the growth timeline expected of H. sapiens is problematic, she says.

Instead, it is likely that Neanderthal infants and H. sapiens babies had significantly different growth rates, implying higher energetic demands in young Neanderthals, she says. However, by about 7 years of age, the growth differences seem to disappear and the children of both species follow a similar trajectory, says Been.

If she had to choose the most likely age of Amud 7, Been says it would be that suggested by the teeth, not the skeleton.

“I think Amud 7 is closer to 6 months old,” she says. “In the first few years of life, from birth through early childhood, Neanderthals grew faster than modern humans.”

This was probably an adaptation to the harsh environments they lived in, says Been, because smaller bodies tend to lose heat more quickly than larger ones.

Chris Stringer at the Natural History Museum in London says Amud 7 fills an important gap in the story of how Neanderthals developed.

“Putting all the evidence together, the researchers identify three different growth stages in young Neanderthals,” he says. Newborn Neanderthals’ teeth generally developed in sync with the rest of their body. Then, in infants and toddlers like Amud 7, there was then a surge in body and brain growth compared with slower dental development. “However, in older children, the dental and body development came back into synchrony, while brain growth continued at a fast rate,” he says.

As adults, Neanderthals were a similar size to H. sapiens, says Been – “though they were on the short side”.