New York: Humans are more intelligent than their nearest living cousins - the chimpanzees - because we undergo a massive explosion in white matter growth during the first two years of life, scientists say.
A new study sheds light on why humans have much bigger brains and are, as a species, much more intelligent, despite sharing 98 percent of the DNA with chimps.
"What`s really unique about us is that our brains experience rapid establishment of connectivity in the first two years of life," LiveScience quoted Chet Sherwood, from the George Washington University, as saying.
"That probably helps to explain why those first few years of human life are so critical to set us on the course to language acquisition, cultural knowledge and all those things that make us human.
"While past studies have shown that human brains go through a rapid expansion in connectivity, it wasn`t clear that was unique amongst great apes (a group that includes chimps, gorillas, orangutans and humans)," said Sherwood.
Researchers carried magnetic resonance imaging (MRI) brain scans of three baby chimps as they grew to 6 years of age. They then compared the data with existing brain-imaging scans for six macaques and 28 Japanese children.
Thy found that chimpanzees and humans both had much more brain development in early life than macaques.
"The increase in total cerebral volume during early infancy and the juvenile stage in chimpanzees and humans was approximately three times greater than that in macaques," the researchers wrote in the journal article.
Human brains, however, expanded much more dramatically than chimpanzee brains during the first few years of life, and most of that human-brain expansion was driven by explosive growth in the connections between brain cells, which manifests itself in an expansion in white matter.
Chimpanzee brain volumes ballooned about half that of humans` expansion during that time period, researchers said.
The explosion in white matter may also explain why experiences during the first few years of life can greatly affect children`s IQ, social life and long-term response to stress.