Neandertal children may have grown up as slowly as modern humans. 

© S.Plailly, E.Daynes/LookatSciences

Neandertals, like humans, may have had long childhoods

Neandertals have long been seen as the James Deans of human evolution—they grew up fast, died young, and became legends. But now, a rare skeleton of a Neandertal child suggests that our closest cousins didn’t all lead such fast lives—and that our own long childhoods aren’t unique. The find may reveal how Neandertals, like humans, had enough energy to grow bigger brains.

“We like the paper because it puts the idea of ‘Neanderthal exceptionalism’ to rest,” wrote anthropologist Marcia Ponce de León and neurobiologist Christoph Zollikofer from the University of Zurich in Switzerland (who are not authors of the new study) in an email. “RIP.”

Researchers have long known that modern humans take almost twice as long as chimpanzees to reach adulthood and have wondered when and why our ancestors evolved the ability to prolong childhood and delay reproduction. Our distant ancestors, such as the famous fossil Lucy and other australopithecines, matured quickly and died young like chimps. Even early members of our own genus Homo, such as the 1.6-million-year-old skeleton of an H. erectus boy, grew up faster than we do.

But by the time the earliest known members of our species, H. sapiens, were alive 300,000 years ago at Jebel Irhoud in Morocco, they were taking longer to grow up. A leading theory is that big brains are so metabolically expensive that humans have to delay the age of reproduction—and, hence, have longer childhoods—so first-time mothers are older and, thus, bigger and strong enough to have the energy to feed babies with such big brains after birth when their brains are doubling in size.

Earlier studies found that Neandertal permanent teeth grew significantly faster and erupted earlier than those of our own species. This suggested that we reach adulthood a few years later than Neandertals, and that our developmental schedule is unique. But a recent study of the skulls of 15 Neandertals by Ponce de León and Zollikofer found that different parts of the brain developed after birth in a pattern similar to modern humans, which suggested Neandertals also had longer childhoods.

This skeleton of a Neandertal boy showed that he grew up slowly, like modern human children.

 

Paleoanthropology Group MNCNCSIC

All of this work had to focus on only one part of the body, because more complete skeletons of Neandertal children are so rare. The discovery of a 49,000-year-old partial skeleton of a child at El Sidrón cave in northwestern Spain offered a chance to compare growth rates across the body and skull. A team led by Spanish researchers measured the maturation of the teeth, skull, spine, elbow, hand, wrist, and knee, assessing the child’s development in a holistic way, says first author Antonio Rosas, a paleoanthropologist at the National Museum of Natural Sciences in Madrid.

Anatomist Christopher Dean of University College London first calculated the age of the child—probably a boy, given the robustness of its bones—at death by counting daily growth lines in slices of one of his molars. The result was 7.7 years, which allowed the team to benchmark the child’s dental growth against data from more than 10,000 modern children from around the world. Then, the team examined computerized tomography scans of his bones to chart how six key places calcified during development. The boy’s limb bones were maturing at the same rate as children his age today, the team reports today in Science.

However, the vertebrae at the center of his spine had not yet fused, unlike those in modern human children of similar age. And the back of the Neandertal child’s skull showed signs that his brain was still growing. The team noted that the child’s brain had reached only about 87% of an average adult Neandertal’s brain size, whereas modern human brains reach 90% of their adult size by age 5. “Neandertals and modern humans are following the same growth pattern, but we have detected some subtle differences,” Rosas says.

Some experts are wary of making sweeping conclusions about Neandertals from the study of only one child. “Neandertal first molars typically grow at a faster rate than modern human molars … which makes this individual unusual,” says paleoanthropologist Tanya Smith of Griffith University in Nathan, Australia, who studies Neandertal tooth development. Also, the brains and bodies of adult Neandertals vary in size, and this individual might have grown up to be a relatively small-brained Neandertal, Ponce de León and Zollikofer say. In their view, these subtle differences are “almost certainly an issue of statistics.”

Rosas hopes to confirm the overall pattern of growth in another partial skeleton of a Neandertal child, such as one in Russia. In the meantime, he says small differences in this boy’s development may offer clues about what makes humans different. Says Rosas: “In this fine modulation, we might find reasons to understand why Neandertals are Neandertals, and modern humans are modern.”