Spring of 2000 found molecular biologists placing dollar bets, trying to predict the number of genes that would be found in the human genome when the sequence of its DNA nucleotides was completed. Estimates at the time ranged as high as 153,000. After all, many said, humans make some 90,000 different types of protein, so we should have at least as many genes to encode them. And given our complexity, we ought to have a bigger genetic assortment than the 1,000-cell roundworm, Caenorhabditis elegans, which has a 19,500-gene complement, or corn, with its 40,000 genes.

When a first draft of the human sequence was published the following summer, some observers were therefore shocked by the sequencing team's calculation of 30,000 to 35,000 protein-coding genes. The low number seemed almost embarrassing. In the years since, the human genome map has been finished and the gene estimate has been revised downward still further, to fewer than 25,000. During the same period, however, geneticists have come to understand that our low count might actually be viewed as a mark of our sophistication because humans make such incredibly versatile use of so few genes.