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What an eight-year-old Neanderthal boy can tell us about how our extinct relatives developed

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Meet El Sidrón J1

The skull of the Neanderthal boy analyzed in the study.
Photo: Paleoanthropology Group MNCN-CSIC

A Neanderthal boy of around eight who died almost 50,000 years ago still has things to tell us: mainly that our extinct human relatives grew up at a pace similar to our own. Knowing that can give us clues to Neanderthal social structure, as well as how our hominid cousins raised their children.

The surprisingly well-preserved specimen, dubbed El Sidrón J1, was found in a Spanish cave of the same name in the 1990s, along with a dozen other family members. His bones — at least the ones we’ve found — are a mix of baby and adult teeth, several vertebrae, ribs, finger bones, leg bones, and parts of his skull. At about eight years of age, when the child died of unknown causes, his body had grown at a similar rate to the body of an eight-year-old modern human. There are just a few peculiar differences: his brain hadn’t stopped growing yet, and the vertebrae in his neck and torso looked like the vertebrae of a four- to six-year-old human kid, according to the new study, published today in Science.

Skeleton of the Neanderthal boy recovered from the El Sidrón cave in Spain.
Photo: Paleoanthropology Group MNCN-CSIC

“It provides the most detailed snapshot of development in Neanderthals that we have,” says Chris Kuzawa, a professor of anthropology at Northwestern University, who did not take part in the study. However, researchers caution that this is just one Neanderthal child — and because every person is different, with different brain sizes and different growth rates, it’s really hard to draw specific conclusions about the entirety of Neanderthals. “This is pulling one person, one Neanderthal individual, from all the people that lived at that time,” Kuzawa tells The Verge. “That’s definitely a big caveat.”

Still, the discovery suggests that, in terms of how they grew and developed after birth, Neanderthals were pretty similar to us. That’s important because it taps into how a species grows and develops, when it matures and reproduces, and ultimately how long it lives. (This is what scientists call a species’s life history.) We modern humans have a fairly slow life history compared to some other primates. Chimps, for example, usually have their first child at 14, and by six, that child can usually live independently. Of course, a six-year-old human child is hardly independent.

Our slow development matters: because kids take longer to mature, parents and others have to take care of them. Our brains don’t reach their full size until we’re about seven, which gives them more time to develop in interactions with our environment and our relatives, which is extra time for learning. “It creates a flexibility and plasticity behaviorally that’s really integral to the human strategy,” Kuzawa says. “There’s this whole constellation of human-like characteristics that likely co-evolved with this stretching of development.”

Neanderthal and modern humans shared a common ancestor roughly half a million years ago, says Tim Weaver, an associate professor in the Department of Anthropology at the University of California, Davis. We then split and evolved in parallel, even breeding with each other, but eventually Neanderthals went extinct and we prevailed. “You can think of Neanderthals as a sort of another experiment in humanity,” says Weaver, who did not take part in the study.

Researchers working inside the El Sidrón cave.
Photo: Paleoanthropology Group MNCN-CSIC

Neanderthals’ life history has been a matter of debate. Some studies that looked at Neanderthal teeth suggested that our human relatives developed a bit faster than us, says Christoph Zollikofer, an anthropologist at the University of Zurich. (Many studies focused on teeth because complete Neanderthal skeletons are hard to come by.) Other studies, however, suggested that Neanderthals had slower life histories than modern humans, because their brains were larger, but didn’t grow faster, Zollikofer writes in an email to The Verge.

Today’s study tries to answer this question by looking at different bones from the partial skeleton of the El Sidrón specimen. First, the researchers analyzed the teeth to determine age. During childhood, a new layer of enamel is laid down on our teeth every day, forming a sort of biological hard drive of our early life. “Teeth grow a little bit like the rings of the trees,” says study co-author Antonio Rosas, a paleobiologist at the Museo Nacional de Ciencias Naturales in Madrid, Spain. Rosas and his colleague counted these rings under the microscope and determined that El Sidrón J1 was 7.7 years old when he died. He didn’t have any major diseases or developmental problems.

The researchers then looked at the child’s bones and teeth, and compared them to the bones and teeth of modern human children. Most bones showed no difference in growth, but some vertebrae in the Neanderthal child’s neck and torso looked like they’d belong to a modern-day human around the ages of four to six. The form of the Neanderthal child’s skull suggests that his brain was still growing, while modern humans reach full brain size around age seven, Kuzawa says. The researchers estimated that the brain of El Sidrón J1 was roughly 87.5 percent of the size of an average adult Neanderthal brain.

“It uses comprehensive evidence from teeth, the brain, vertebrae and the rest of the skeleton to show that Neanderthals did not develop faster than humans,” says Zollikofer, who was not involved in the research. “This is important, because it was kind of ‘common wisdom’ for many years that they did.”

In this specimen, the brain seems to be developing even more slowly than in humans. If that’s true, it could mean that Neanderthals also had to take care and nurture their children for even longer than we do today. But there’s an important caveat: there’s variation among adult Neanderthal brains, says Zollikofer. If a lower value is used for “normal” brain growth, then El Sidrón is comparable to a normal human kid. Weaver agrees: “There’re definitely some statistical issues there.”

Antonio Rosas beside the Neanderthal child’s skeleton.
Photo by Andrés Díaz-CSIC Communication

The El Sidrón specimen is also just one Neanderthal child, among many Neanderthals that all had their own specific traits and peculiarities. So it’s not wise to draw conclusions about all Neanderthal children based on this one brain. In order to settle the controversy on brain size conclusively, we’ll need more samples, so the scientists will keep digging.