Back

Psychologists like using twins in studies that are concerned with the nature or nurture question. The reason is simple: twins are more similar in terms of their genetic and their environmental factors than unrelated people or even non-twin siblings.

It should be fairly obvious why identical twins are so similar: they both have the identical genetic code (well, excepting the possibility of some minor mutations). This means that they have the same gentics. In the debate between nature and nurture, identical twins have, effectively, the same nature. If you want to look at the affect that environmental conditions, for example, have on people, by using identical twins you can eliminate variability due to genetic factors.

Fraternal twins do not share the same genetic code. They are, in effect, just two siblings that are born at the same time. So, while fraternal twins can not be used to control for genetic variability, they may show less environmental variability that siblings born several years apart, for example. Consider: fraternal twins, especially if they are of the same sex, probably will go to the same school, may watch the same television programs, be enrolled in similar extracurricular activities, etc. Hence, while it is impossible to completely control for environmental variability fraternal twins can allow one to study issues of genetic difference while reducing environmental factors.