In the angry debate over how much of IQ comes from the genes that children inherit from parents and how much comes from experiences, one little fact gets overlooked: no one has identified any genes (other than those in the case of retardation) that affect intelligence. So researchers led by Robert Plomin of London's Institute of Psychiatry decided to look for some. Plomin's colleagues drew blood from two groups of 51 children each. They are all White living in six counties around Cleveland. In one group, the average IQ is 136.@In the other group, the average IQ is 103.@Isolating the blood cells, the researchers then examined each child's chromosome 6 (One of 23 human chromosomes along which genes made of DNA). Of the 37 landmarks on chromo-some 6 that the researchers looked for, one jumped out: a form. of gene called IGF2R occurred in twice as many children in high-IQ group as in the average group—32 percent versus 16 percent. The survey concludes that it is this form. of the IGF2R gene, called allele 5, that contributes to intelligence. Plomin cautions that 'this is not a genius gene. h is one of many.' (About half the differences in intelligence between one person and another are thought to reflect different genes, and half reflect different life experiences.) The gene accounts for no more than four extra IQ points. And it is neither necessary nor sufficient for high IQ: 23 percent of the average-IQ kids did have it, but 54 percent of genius kids did not. The smart gene is known by the interesting name 'insulinlike growth factor 2 receptor' (IGF2R to its fun). It lets hormones like one similar to insulin dock with cells. Although a gene involved with insulin is not the most obvious candidate for an IQ gene, new evidence suggests it might indeed play the role. Sometimes when a hormone docks with the cell, it makes the cell grow; sometimes it makes the cell commit suicide. Both responses could organize the development of the brain. Scientists at the National Institutes of Health find that insulin can stimulate nerves to grow. And in rat brains, regions involved in learning and memory are chock full of insulin receptors. Even though this supports the idea that IGF2R can affect the brain and hence intelligence, some geneticists see major problem with the IQ-gene study. One is the possibility that Plomin's group fell for what's called the chopsticks fallacy. Geneticists might think they've found a gene for chopsticks skill, but all they've really found is a gene more common in Asian than, say, Africans. Similarly, Plomin's IQ gene might simply be one that is more common in groups that emphasize academic achievement. 'What if the gene they've found reflects ethnic differences?' asks geneticist Andrew Feinberg of Johns Hopkins University. 'I would take these findings with a whole box of salt.' As for how much of IQ comes from genes and how much comes from experiences.