What made human brains bigger than that of chimps

Researchers have discovered a tiny difference in a particular regulator of gene activity that human brain is bigger than that of our closest living relative, the chimpanzee who have almost all of of the genes that we have.

The researchers spotted the difference in gene activity regulatory called HARE5, located near a gene called Frizzled 8, which is linked to brain development and disease.

When introduced into a mouse embryo, human HARE5 mice had brains 12 percent larger in area compared with chimpanzee HARE5 mice, the findings showed.

"What we found is a piece of the genetic basis for why we have a bigger brain," said co-author Gregory Wray, professor at the Duke University in the US.

The findings may lend insight into not only what makes the human brain special but also why people get some diseases, such as autism and Alzheimer's disease, whereas chimpanzees do not.

The size of the human brain expanded dramatically during the course of evolution, imparting us with unique capabilities to use abstract language and do complex maths.

In the new study, researchers mined databases of genomic data from humans and chimpanzees, to find enhancers expressed primarily in the brain tissue and early in development.

They prioritised enhancers that differed markedly between the two species.

The human HARE5 and the chimpanzee HARE5 sequences differ by only 16 letters in their genetic code. Yet, in mouse embryos the researchers found that the human enhancer was active earlier in development and more active in general than the chimpanzee enhancer.

The researchers said they would study the human HARE5 and chimp HARE5 mice into adulthood, for possible differences in brain structure and behaviour.

The findings appeared online in the journal Current Biology.