Scientists have found it most valuable to study the cases of twins in order to determine the relative contribution of genetics or environmental factors to intelligence. First off, it is important to have an understanding of the genetic distribution between the different groups. Identical twins share the exact same genetic material, giving them 100% genetic overlap. Secondly, all other first degree family members such as fraternal twins, siblings, and biological parents and children share 50% genetic overlap. Cousins have 15% overlap, and all other relationships share 0% genetic overlap.
In twin studies, psychologists study a variety of different cases; identical twins raised together, identical twins raised separately, and fraternal twins raised together and separately. The reason for including these groups is to examine the correlation they have for intelligence. These studies have shown the intelligence correlation in identical twins is higher than in fraternal twins, even when the identical twins are raised apart. Examining these different groups helps to determine the influence both genetics and environmental factors have on intelligence.
Other groups that have been included in these studies are: siblings raised together, siblings raised apart, biological parent and child that lived together, biological parent and child that lived apart, adoptive parent and child that lived together, and cousins that lived apart. These groups were included because comparing identical versus fraternal twins is not the only method to help determine the influence of genetics on intelligence. Because these other groups have varying degrees of genetic overlap with each other, they provide information that can contribute to understanding the relative contribution of heredity versus environment.
There are many different benefits that will come with knowing whether or not genetics or environmental factors play the largest role in intelligence. First, if it turns out that intelligence is most directly associated with environment, then advances can be made in both household and school settings to make the environment more conducive to intellectual gains. On the other hand, if these studies produce results showing that intelligence is largely based on genetics, a whole new realm of possibilities is opened. The consequences of this discovery could lead to research that would allow geneticists to change a person’s intelligence. This is just one possibility, but that topic is beyond the scope of this paper.
These studies provide evidence that gives both genetics and environment have an influence on intelligence. Psychologists have determined the intelligence correlations of all of the different groups mentioned above. The intelligence correlation between identical twins raised together is .86. Those who support the environmental views of intelligence argue that this high correlation can be attributed to the twins being treated alike within their...