What Makes You Who You Are

The perennial debate about nature and nurture–which is the more potent shaper of the human essence? –is perennially rekindled. It flared up again in the London Observer of Feb. 11, 2001. REVEALED: THE SECRET OF HUMAN BEHAVIOR, read the banner headline. ENVIRONMENT, NOT GENES, KEY TO OUR ACTS. The source of the story was Craig Venter, the self-made man of genes who had built a private company to read the full sequence of the human genome in competition with an international consortium funded by taxes and charities.
That sequence–a string of 3 billion letters, composed in a four-letter alphabet, containing the complete recipe for building and running a human body–was to be published the very next day (the competition ended in an arranged tie). The first analysis of it had revealed that there were just 30,000 genes in it, not the 100,000 that many had been estimating until a few months before. Details had already been circulated to journalists under embargo. But Venter, by speaking to a reporter at a biotechnology conference in France on Feb. , had effectively broken the embargo. Not for the first time in the increasingly bitter rivalry over the genome project, Venter’s version of the story would hit the headlines before his rivals’. “We simply do not have enough genes for this idea of biological determinism to be right,” Venter told the Observer. “The wonderful diversity of the human species is not hard-wired in our genetic code. Our environments are critical. ” In truth, the number of human genes changed nothing.
Venter’s remarks concealed two whopping nonsequiturs: that fewer genes implied more environmental influences and that 30,000 genes were too few to explain human nature, whereas 100,000 would have been enough. As one scientist put it to me a few weeks later, just 33 genes, each coming in two varieties (on or off), would be enough to make every human being in the world unique. There are more than 10 billion combinations that could come from flipping a coin 33 times, so 30,000 does not seem such a small number after all.

Besides, if fewer genes meant more free will, fruit flies would be freer than we are, bacteria freer still and viruses the John Stuart Mill of biology. Fortunately, there was no need to reassure the population with such sophisticated calculations. People did not weep at the humiliating news that our genome has only about twice as many genes as a worm’s. Nothing had been hung on the number 100,000, which was just a bad guess. But the human genome project–and the decades of research that preceded it–did force a much more nuanced understanding of how genes work.
In the early days, scientists detailed how genes encode the various proteins that make up the cells in our bodies. Their more sophisticated and ultimately more satisfying discovery–that gene expression can be modified by experience–has been gradually emerging since the 1980s. Only now is it dawning on scientists what a big and general idea it implies: that learning itself consists of nothing more than switching genes on and off. The more we lift the lid on the genome, the more vulnerable to experience genes appear to be.