Researchers from the Kyoto University in Japan found that human and chimp brains begin to show remarkable differences very early in life.
"Nobody knew how early these differences between human and chimp brains emerged," said Satoshi Hirata of Kyoto University.
In both primate species, the brain grows increasingly fast in the womb initially.
After 22 weeks of gestation, brain growth in chimpanzees starts to level off, while that of humans continues to accelerate for another two months or more. (Human gestation time is only slightly longer than that of chimpanzees, 38 weeks versus 33 or 34 weeks.)
The findings are based on 3D ultrasound imaging of two pregnant chimpanzees from approximately 14 to 34 weeks of gestation and comparison of those fetal images to those of human fetuses.
While early brain differences were suspected, no one had previously measured the volume of chimpanzee brains as they develop in the womb until now.
"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 behaviour," researcher Tomoko Sakai said in a statement.
The team now hopes to explore fetal development in particular parts of the brain, including the forebrain, which is critical for decision making, self-awareness, and creativity.
The study was published in the journal Current Biology.
