Copernican demotion is a habit of biologists, too. Charles Darwin told us we were just another species among millions. In the 1950s, cytologists found we had one fewer pair of chromosomes than gorillas or chimpanzees—hardly good for our self-esteem. Anthropologists reported that apes could make tools, while paleontologists told us that our brains are possibly smaller than those of Neanderthals. Then came the news that, even within our own species, relative brain size had been shrinking, not growing, over the past 10,000 years.
Geneticists were no help either. In the 1960s, they discovered the startling fact that we had one-third as much DNA as grasshoppers and one-tenth as much as salamanders. For a while we stroked our egos by telling ourselves that we must have special genes to build and run our special brains. But it turned out not to be true. When the genome was sequenced at the turn of this century, and the genes counted, it transpired that we have the same number of genes as a mouse. Indeed, give or take a handful, we have the same genes as a mouse, just switched on in a different order and pattern.
Even when uniquely human features did emerge, they were humiliatingly mundane. In the 1990s, biochemists, led by Ajit Varki of the University of California at San Diego, found that about three million years ago, human beings developed a different version of a sugar called sialic acid on cell surfaces, possibly as a defense against malaria parasites. Intriguing, but hardly the key to the soul.
Now, at last, comes news that a team of scientists led by Daniel Geschwind of the University of California, Los Angeles has found something special about the human brain. Using the latest gene sequencing machines and gene chips, they have compiled the “transcriptome” of the human “telencephalon,” which means (in plain English) that they have identified those genes that are active in the main part of the brain. They then compared this list with equivalent data from chimpanzees and macaque monkeys.
What they found was that the frontal lobe of the human brain—the bit that seems to determine personality—stood out as unusual, even compared with the closely related chimpanzee. “Our analysis reveals a predominance of genes differentially expressed within the human frontal lobe and a striking increase in transcriptional complexity specific to the human lineage in the frontal lobe.”
What’s intriguing about the new results is not just that more genes seem to be active in the human frontal lobe, especially those involved in letting brain cells link with each other, but that the extra complexity clusters around certain “hub” genes. One of these is FOXP2, a gene that is known to be crucial to the development of language. In apes, monkeys and mice, FOXP2, seems to have fewer other genes at its beck and call than in human beings. As Mr. Geschwind’s team puts it, “we experimentally validate an enrichment of human FOXP2 target genes” in the human frontal lobe.
A Copernican promotion at last?
Write to Matt Ridley at firstname.lastname@example.org
A version of this article appeared September 1, 2012, on page C4 in the U.S. edition of The Wall Street Journal, with the headline: At Last, Humans Get a Scientific Promotion.