Neanderthal Boy Found in Spanish Cave Was Human-Like, but With a Larger Brain

Neanderthals were brainier than modern humans, and new research helps to explain how these early hominids evolved so much brain power.

El Sidrón Cave in northwestern Spain preserved the remains of at least 12 Neanderthals for about 49,000 years until their discovery in 2010. Genetic evidence suggests the group — 3 adult males, 3 adult females, 3 adolescent boys, 2 juveniles, and an infant — were all related. What they were doing in the cave before their demise has intrigued archaeologists and historians since the incredible discovery.

New research on the related individuals, however, began with different, yet no less important, questions: How was Neanderthal physiological development different from that of modern humans, and how and why did Neanderthals evolve such big brains?

It has long been reported that the average Neanderthal adult brain had a volume of approximately 1520 cubic centimeters (92 cubic inches), while the average size of a modern human brain is about 1450 cubic centimeters (88 cubic inches).

Bigger brains are not necessarily always better, though, in terms of intellect. Honeybees, for example, are among the most intelligent insects, yet they obviously have very tiny brains.

Nevertheless, “Neanderthals certainly had, in their own way, a sophisticated intellect in evolutionary terms,” Antonio Rosas, a paleoanthropologist at the National Museum of Natural Sciences in Madrid, told Seeker.

Skeleton of a Neanderthal boy recovered from El Sidrón Cave in Asturias, Spain |Paleoanthropology Group MNCN-CSIC

Rosas and his colleagues conducted the new physical analysis, focusing on just one of the unearthed Neanderthals, a well-preserved boy dubbed El Sidrón J1, whose mix of baby and adult teeth suggests that he died at 7.69 years of age. The findings of the study, published in the journal Science, consist primarily of three determinations.

First, as co-author Luis Ríos of the museum and the Aranzadi Society of Sciences said during a teleconference with media, “there was no noticeable difference in the growth and maturation of this Neanderthal juvenile in comparison with modern human juveniles.”

The observed similarities could help to explain how Neanderthals and anatomically modern humans interbred: Even today, people of European and Asian descent retain Neanderthal DNA. Intriguingly, arctic indigenous peoples and East Asians today possess the biggest brains in the world. They also retain a higher percentage of early hominid — Neanderthal and Denisovan — DNA than most of us.

Their big brains may be a legacy of that heritage. Climate and latitude could be other factors affecting brain growth, along with nutrition.

The second major finding of the study is that the Neanderthal boy’s brain was still likely growing when his life was cut short. While the researchers do not yet know how he and the other Neanderthals died, they can compare other braincases with that of the remains of this young fellow.

The comparison showed that his brain was roughly 87.5 percent of the size of an average adult Neanderthal brain. A modern human of the same age, on average, tends to have 95 percent of the adult brain weight.

“This longer period of growth may have allowed larger brains and larger bodies to grow,” Rosas said. Although Neanderthals had broader bodies than modern humans, he added, their brain to overall body size ratio was still larger than that of our species. It could then be said that they had more brainpower.

Many researchers over the years have wondered why these brainy individuals then went extinct, but because Neanderthal DNA remains in current populations, these hominids were probably just absorbed into what is now known as Homo sapiens.

Researchers working inside El Sidrón Cave in Asturias, Spain |Paleoanthropology Group MNCN-CSIC

Since Neanderthal childhood development happened rather slowly, this suggests that youths spent a lot of time with parents, older relatives, and other guardians.

“That allowed them to have more time for learning, as compared to other earlier Homo species,” Rosas said. “However, it is difficult to evaluate the biological meaning of the extra learning time as compared to modern humans.”

The third and final finding of the study is that some vertebrae in the boy had not fused when he died. This is another contrast with modern humans, whose same vertebrae tend to fuse around the ages of 4 to 6 years old. The researchers do not think that the difference was due to some pathology in the boy, but rather was probably a development trait of all Neanderthals.

There was “no evidence of disease in the skeleton” of the boy, Rosas said.

Prior research determined that adult male Neanderthals stood about 5 feet 5 inches, which is only 2 inches shorter than the average height for men in many parts of Asia today. As of 10,000 years ago, European males measured about 5 feet 4 inches, reflecting a likely shrinkage before human height globally began to rise again in most regions in more recent years.

Debate continues over what species was the last common ancestor of Neanderthals and modern humans. Rosas said that some people think the last common ancestor “was Homo heidelbergensis; others think it was an earlier species, such as Homo antecessor.” Determining the answer could pinpoint when bigger brains emerged in the human lineage.

In the meantime, the researchers are focused on the El Sidrón Cave discoveries.

Because different generations of related Neanderthals were found in this same cave, their remains provide a unique opportunity to study the physical development of these hominids, which were so similar to us, yet subtlety different, as the new study shows.

Rosas said that he and his team next hope to explore aspects related to adolescence and growth, especially in the infant to childhood transition that occurred in Neanderthals. In addition to revealing more about these early hominids, the work could provide important insights into our own biology — whether we are related to Neanderthals, or not.

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