WASHINGTON: What makes humans different from chimps, apart from a little extra hair? It might be a more creative use of the genes that affect how the brain works, a study suggests.

Humans and chimps share 98.7 per cent of their DNA, but are clearly very different. Scientists have long tried to determine how just over one per cent of our genes can make such a difference.

It may not be an issue of quantity, but of quality, an international team of genetics experts reports in this week’s issue of the journal Science. And the differences seem to lie mostly in the brain.

“When you look at blood, you don’t see a lot of differences. Chimps look very, very much like us,” Ajit Varki of the University of California San Diego, who helped direct the research, said in an interview.

“But when you look at brain you see a lot of differences.”

The findings could go a long way to soothing humans flustered at learning that we have fewer genes than even some plants. Public and private teams who sequenced the human genome estimate that we have only about 30,000 to 40,000 genes as compared to, for instance, 50,000 for rice.

Genomics experts say it is not how many genes you have that counts, but what you do with them — in this case the protein products of genes.

The work by Varki and colleagues, including noted genetics expert Svante Paabo of the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, Germany, supports this.

They found five times as many changes in gene expression — actual activity by the genes — in the human brain than would be predicted by evolution.

“If two species have been apart for five million years, you expect a certain amount of differences,” Varki said. But there are many more differences in the human brain than expected.

“Whereas if you look at liver and blood, you don’t see that,” Varki added.

The researchers look at messenger RNA, which is what translates the genetic recipe found in DNA into a final product — a protein. Every cell contains a full complement of DNA, but what makes one cell become a liver cell and another function as a brain cell depends on what genes are expressed.

They took many different samples of tissue from human cadavers, chimps and orangutans that had died of natural causes, monkeys and mice, and compared them.—Reuters