Neanderthals have long been portrayed as our ignorant, tough cousins. Now, ground-breaking research – although it did not confirm the stereotype – has revealed striking differences in the brain development of modern humans and Neanderthals.
The study involved inserting a Neanderthal brain gene into mice, ferrets and “mini-brain” structures called organoids, grown in the lab from human stem cells. The experiments revealed that the Neanderthal version of the gene was linked to slower formation of neurons in the brain’s cortex during development, which the researchers said could explain superior cognitive abilities in modern humans.
“Making more neurons sets the stage for higher cognitive function,” said Wieland Huttner, who led the work at the Max-Planck-Institute of Molecular Cell Biology and Genetics. “We believe this is the first convincing evidence that modern humans were cognitively superior to Neanderthals.”
Modern humans and Neanderthals split into separate lineages around 400,000 years ago, with our ancestors remaining in Africa and the Neanderthals moving north into Europe. About 60,000 years ago, a mass migration of modern humans out of Africa brought the two species face to face again and they interbred – modern humans of non-African heritage carry 1-4% Neanderthal DNA. By 30,000 years ago, however, our ancient cousins had disappeared as a distinct species, and the question of how we out-competed Neanderthals has remained a mystery.
“A concrete fact is that wherever homo sapiens went, they would basically outcompete other species there. It’s a bit strange,” says Professor Laurent Nguyen, of the University of Liège, who was not involved in the latest research. “These boys [Neanderthals] were in Europe long before us and would have adapted to their environment including pathogens. The big question is why we would be able to outperform them.”
Some argue that our ancestors had an intellectual advantage, but until recently there has been no way to test the hypothesis scientifically. This changed in the last decade when scientists successfully sequenced Neanderthal DNA from a fossilized finger found in a Siberian cave, paving the way for new insights into how Neanderthal biology differed from our own.
The latest experiments focus on a gene, called TKTL1, involved in neuronal production in the developing brain. The Neanderthal version of the gene differs by one letter from the human version. When inserted into mice, the researchers found that the Neanderthal variant led to the production of fewer neurons, particularly in the frontal lobe of the brain, where most cognitive functions reside. The researchers also tested the effect of the gene in ferrets and blobs of lab-grown tissue, called organoids, which replicate the basic structures of the developing brain.
“This shows us that although we do not know how many neurons the Neanderthal brain had, we can assume that modern humans have more neurons in the frontal lobe of the brain, where [the gene’s] activity is highest than Neanderthals,” said Anneline Pinson, first author of the study.
Chris Stringer, head of research into human origins at the Natural History Museum in London, described the work as “groundbreaking” and said it began to solve one of the central puzzles of human evolution – why, with all the past diversity of humans, we are now the only ones left.
“Ideas have come and gone — better tools, better weapons, proper language, art and symbolism, better brains,” Stringer said. “Finally, this provides a clue as to why our brains may have surpassed those of Neanderthals.”
More neurons does not automatically equal a smarter type of person, although that dictates the basic computing capacity of the brain. Human brains contain about twice as many neurons as the brains of chimpanzees and bonobos.
Nguyen said the latest work is far from definitive proof of modern humans’ superior intellect, but shows that Neanderthals had meaningful differences in brain development. “This is an exciting story,” he added.