It is clear that intelligence is in part inherited. Studies of identical twins raised in different environments show that about 50% of a person's intelligence can be explained by inheritance; the other half is explained by the environment experienced during rearing. What gene or genes are responsible for intellectual brilliance? A study published in the journal Molecular Psychiatry by Davies and colleagues at the University of Edinburgh has found an answer.
Intelligence is strongly associated with many aspects of life. People with higher intelligence tend to have more professional occupations, higher incomes, and live longer lives. Identifying the genes responsible for high intelligence could provide important insight into human cognition that would have wide-ranging medical and social significance. In their study analyzing DNA from thousands of unrelated adults ranked according to performance on intelligence tests, they found no single gene or set of genes that could explain the variation in intelligence. Instead, they conclude that human intelligence is due to small variations in a large number of different genes.
Their work confirms that although your level of intelligence is largely determined by the particular genes you inherited from your parents, no single "smart" gene or combination of genes can be pin-pointed to explain the effects of genetics on intelligence. Like a master chef preparing a savory dish, genes control development of the human brain, but it is not the genetic ingredients themselves that explain the outcome, but rather the combination and subtle variations in how they are used that determine how smart you are.
See: Davies, G., et al., (2011) Genome-wide association studies establish that human intelligence is highly heritable and polygenic. Molec. Psychiat. 16, 996-1005.