With all the hoopla over the genome lately, one might expect DNA sequences to finally reveal exactly what it is that makes us human. But findings presented last week at the Human Genome Meeting in Edinburgh, Scotland, suggest that gene activitynot sequenceholds the key to our identity.

Comparing three million letters of the chimpanzee genetic code with the human genome draft, Svante Pbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and his colleagues found only a 1.3 percent difference between the two. Taking that into consideration, the team concluded that something other than the makeup of the genes themselves must account for what sets us apart from our closest living relatives.

Pbo's group thus turned their attention to levels of gene activity, or transcription. Specifically, they looked at transcription in the brain, liver and blood of humans, chimps and rhesus macaque monkeys. Whereas liver and blood gene activity patterns showed the expected differences among the three groupswith human transcription looking similar to that of the chimp, and different from that of the more evolutionarily distant macaquegene activity in the brain revealed stark differences between humans and chimps. "The [human] brain has accelerated usage of genes," Pbo remarked, according to Nature News Service.

Differences in gene expression may thus explain how largely similar genomes create such different organisms. Still, fully understanding the genetic differences between humans and chimps will require actually getting inside the chimpanzee's mind.