Still, psychologists continue the debate, with a majority sympathetic to the general-intelligence perspective. This is by and large a Western question. In the Confucian societies of East Asia individual differences in endowment are assumed to be modest, and differences in achievement are thought to be due largely to effort. By the same token, the IQs of identical twins are more similar than the IQs of fraternal twins. Still, because of the intricacies of behavioral genetics and the difficulties of conducting valid experiments with human child-rearing, a few defend the proposition that intelligence is largely environmental rather than heritable, and some believe that we cannot answer the question at all.
Cultural assumptions are evident in early intelligence tests.
Others are more subtle. Suppose the question is what one should do with money found on the street. Only the canonical response to such a question would be scored as correct. Psychometricians have striven to remove the obviously biased items from such measures. But biases that are built into the test situation itself are far more difficult to deal with.