Intelligence quotients have largely been proven to be an accurate assessment of cognitive abilities, but there is some disagreement as to whether IQ is hereditary or environmental and whether average IQ is increasing or increasing. Many eugenicists believe that IQ is largely genetic and since people with lower IQs are less likely to use birth control that the percentage of stupid people is increasing (like in Idiocracy), they call this phenomenon a dysgenic event. However there is much more documentation suggesting that average IQ, especially towards the lower end of the scale, is increasing by at least 3 points every 30 years, known as the Flynn effect. It is known that some genes such as FADS2 and CHRM2 have an influence on IQ, but children from lower income families also tend to score lower on IQ tests. Studies seem to show that environment is a bigger influence in lower income families and genetics is a bigger influence in higher income families, in all cases biological siblings show less variation in IQ than adopted ones. Since living conditions tend to be better (or at least more stable) in higher income households this seems to suggest that IQ might be like height, the upper limit is determined by genes but poor living conditions may prevent one from reaching that limit. It is certainly undeniable that nutritional and educational standards have increased (at least in the west) over the past century, which would account for the Flynn effect. But if there is a genetic upper limit the increase should at least be slowing down, which some think is happening in Denmark and some other developed nations.