A new study sheds light on why humans are so much more intelligent than chimpanzees despite sharing almost 99% of the same DNA.
Though humans have much the same genes as chimps, it seems that this genetic information can behave differently in the two species.
When researchers looked how genes operate in human and chimp livers, brains and blood, they found the biggest differences in the brains.
The work could help understand how humans evolved and why some diseases affected the two species differently, Dr Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told BBC News Online.
Chimpanzees infected with HIV tend not to contract AIDS.
The species also tends to contract different types of cancer.
"Chimpanzees tend to have a lot fewer tumours in epithelial tissues like the breast, colon, and prostate but just as much leukaemia," said Dr Pääbo.
An insight into why this happens might have the potential to lead to new therapies.
Dr Pääbo’s team compared brain and liver tissue samples from three humans and three chimpanzees, all of whom had died of natural causes.
’Gene chip’ analysis
They also took blood samples from live subjects.
They used microarrays known as "gene chips" to examine how each of around 12,000 human genes was functioning in the tissue.
The reason the human-chimp differences are biggest in the brain tissue samples is, they suspect, a consequence of the way human genes in the organ changed rapidly during evolution.
This adaptation might explain how humans came to be so much more intelligent than their ape counterparts.
Mountain to climb
It also serves to highlight the complexity of the task of making sense of the mountains of data produced by endeavours such as the human genome project.
Scientists need to do more than know how many genes we have and where they lie on our chromosomes; they also need to discover how these genes work in living bodies.
For, as the Leipzig study shows, the same genes can work in different ways.
"We’re going to be looking now at why the differences exist," Dr Pääbo said.
"We want to focus much more on the brain and find out if there are bits of the brain which did not undergo accelerated development in humans."
He and his colleagues describe their work in the journal Science.
By Ivan Noble
BBC News Online
April 11, 2002