With brains as big as ours, Neandertals were no dumb brutes. But their brains may have developed in a manner much different from the way ours do, according to anew study. The differences suggest that Neandertals did not see the world the same way we do and may not have been as adept at language or forming complex social networks.
Paleoanthropologists Jean—Jacques Hublin, Philipp Gunz, and Simon Neubauer of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, made the find by first comparing CT scans of the brains of 58 humans and 60 chimps, varying in age from birth to adulthood. The researchers used three—dimensional imaging and several hundred landmarks on the braincases to match the brains accurately despite differences in size. As the team reports this month in the Journal of Human Evolution, humans—but not chimps—preferentially expand their parietal lobes and cerebellums and widen their temporal lobes in the first year of life. This results in the characteristic rounded dome of our skulls.
In another study published online today in Current Biology, the researchers and a colleague used the same imaging methods to study nine fossil Neandertals, including a newborn, a year—old baby, and three children. Because the brain does not fossilize, they studied endocasts, imprints of the brain left in the skull. They found that at birth, both Neandertal and modern human infants had elongated braincases that were similar in shape, although Neandertal faces were already larger. But by age 1 or so, modern humans had grown globular brains, whereas Neandertal babies had not; like chimpanzees, they did not show the preferential bulging in the parietal and cerebellar regions, even though the brain grew overall.
"Although they have the same brain size as us, Neandertals missed something that humans got in the first year of life," says Hublin. Injuries or differences in development in those regions have been linked to deficits in speech and social interaction in people, he notes, suggesting that Neandertals may not have been as good at language, trade, and other behaviors that allowed humans to form complex societies.
Paleoneurologist Emiliano Bruner of the National Research Centre on Human Evolution in Burgos, Spain, praises the findings. "They finally demonstrate that this stage [bulging] is absent in Neandertals," he says. But anthropologist Marcia Ponce de León of the University of Zurich in Switzerland, worries that the sample size was too low, noting that the new analysis depends on endocasts of just one incomplete skull of a Neandertal newborn and of an older baby. Hublin and Gunz acknowledge the sample size problem but respond that they also used computer simulations of growth that did not rely on juvenile fossils. When they modeled the development of modern human babies without a globular growth stage, the babies grew up to look like Neandertal adults. They also say that they've recently confirmed their findings in a second, more complete Neandertal newborn.
The team is now investigating how brain development may be linked to genes that differ between Neandertals and modern humans, working with the Max Planck researchers who sequenced the Neandertal genome. "Very small differences in this crucial time in development can have serious consequences," says Gunz.