The Cosmos in Our Heads

Over-exuberant press accounts of recent genetic linkage studies have led the public to believe that there is a “gay gene,” a “gene for novelty-seeking,” a “gene for happiness” and a gene for just about every other human idiosyncrasy. But to biologists who study even comparatively simple animals such as the fruit fly, it’s laughable to speak of any single gene as determining behavior. Time, Love, Memory, Jonathan Weiner’s first book since his Pulitzer Prize-winning The Beak of the Finch, is about a little-known Caltech geneticist named Seymour Benzer and his innovative experiments on bacteria-eating phage and Drosophila fruit flies. By tracing four decades of Benzer’s painstaking work, Weiner shows that biology’s picture of the relationship between genes and behavior is growing more baroque, not less.

A year after James Watson and Francis Crick solved the structure of DNA in 1953, Benzer proved that genes are physical entities that can be dissected and put back together, a fact that allowed him to draw the first detailed map of a gene’s interior. This helped Crick and colleague Sydney Brenner to decipher how DNA’s four nucleotides (A, C, G and T) encode amino acids and proteins, and to show that most mutations-whether in phage, flies, or philosophers-are due to simple typographical errors in this code.

This was the thread, Benzer realized, that might allow biologists to unravel the genetic differences behind “the innumerable quirks of our bodies and minds,” as Weiner puts it. He began to study fly strains with aberrant circadian cycles. His lab showed in 1967 that three such strains all had mutations in the same region of their X chromosomes, implying that the region harbors a “clock” gene. Named period, this gene has since been found in organisms from mice to men, and is famous among biologists as one of the first to be associated with a specific behavior.

But that was only the beginning of the story. Period and another gene called timeless turn out to encode proteins with the ability to switch off their own production once they reach a certain concentration inside brain cells. Production is switched back on by other proteins, and all of these proteins mesh with still more genes and proteins in what Weiner poetically calls “a kind of orrery in the heart of every one of our cells…a model of the cosmos inside our heads that cycles whether we are in or out of the sun.”

Every new fruit fly mutation seems to reveal a new gear in the orrery. Even the simplest behaviors arise from genetic interactions so numerous and interlaced that scientists like Benzer are only beginning to understand them.Weiner’s book is the most deft, level-headed explanation of this fact I’ve seen. It’s enough to make one believe in a gene for good writing.