A new study from Kyoto University shows that human’s superior brain size in comparison to chimpanzees can be traced back to the womb. Appearing in the September 25 issue of Current Biology, the study is the first to track and compare brain growth in chimp and human fetuses.
“Nobody knew how early these differences between human and chimp brains emerged,” said Satoshi Hirata of Kyoto University.
Hirata’s research team, which included Tomoko Sakai and Hideko Takeshita, finds that human and chimp brains begin to show remarkable differences at very early stages. Both species of primates show increasingly rapid brain development in the womb compared to other mammals. After 22 weeks of gestation, however, chimpanzee brain growth begins to level off, while human growth continues to accelerate for another two months or more. Gestational periods are only slightly different between the species – 38 weeks for humans and 33 to 34 weeks for chimpanzees.
The team used 3D ultrasound imaging at approximately 14 to 34 weeks of gestation to compare chimpanzee and human fetal images. While early brain development differences have been suspected, no one had previously measured the volume of chimpanzee brains as they developed in the womb until now.
The research team made these findings as part of a larger effort to explore the differences in primate brains. Last year they compared brain development differences via magnetic resonance imaging (MRI) scans of three growing chimpanzees from the age of six months to six years.
“Elucidating these differences in the developmental patterns of brain structure between humans and great apes will provide important clues to understand the remarkable enlargement of the modern human brain and humans’ sophisticated behavior,” Sakai said.
The next step, the team says, is to chart the fetal development of particular parts of the brain, including the forebrain, which is critical for decision making, self-awareness, and creativity.
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