My latest Mind and Matter column at the Wall Street
Journal:
The astronomer Martin Rees recently coined the neat phrase “Copernican demotion”
for science’s habit of delivering humiliating disappointment to
those who think that our planet is special. Copernicus told us the
Earth was not at the center of the solar system; later astronomers
found billions of solar systems in each of the billions of
galaxies, demoting our home to a cosmic speck.
Mr. Rees says further Copernican demotion may loom ahead. “The
entire panorama that astronomers can observe could be a tiny part
of the aftermath of ‘our’ big bang, which is itself just one bang
among a perhaps-infinite ensemble.” Indeed, even our physics could
be a parochial custom: Mr. Rees says that different universes could
be governed by different rules and our “laws of nature” may be
local bylaws.
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 at San Francisco 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?