The Flynn Effect is the phenomenon in which there is a marked increase in intelligence test score averages over time. This has been reported to happen worldwide. Intelligence testing began in the 1930s and the average scores have steadily increased since then. Intelligence tests are standardized at a score of 100 which means that 100 is the average score of all who take it.
When a test is revised they are standardized to a score of 100 again so that it is certain they are measuring correctly in relation to the new group of test takers. When a new group of people take the previous test there is an increase in scores with the new group typically scoring well above 100 (which is the average). There are many possible explanations for the Flynn Effect including better nutrition, less infectious disease, longer and more productive education, and more stimulating environments.