The distribution of IQ among humans is described by the normal distribution having a mean of 100 and standard deviation of 15. In this description, the percentage of people with IQ less than 10 is virtually zero. At levels below 50, and above 150, IQ doesn’t have much meaning. Someone with an IQ below 50 is barely functioning, while someone with IQ above 150 has an intelligence that cannot be measured with any precision using an IQ test.
While IQ tests are good instruments for determining learning abilities in humans, they have a limited range of validity at the extremes. They are also of limited value in assessing the kinds of intelligence that we see in non-human animals.
If we humans were more intelligent, we would have better devices for measuring the different kinds of intelligence that exist. Einstein is reputed to have observed, “Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”
