Twin studies are one of the foundations of modern human genetics. Researchers take advantage of a basic biological fact (that identical or monozygotic twins share essentially 100% of their genomes while fraternal or dizygotic twins share 50%) to study to what degree certain traits (disease risk, etc.) are heritable (i.e., how much of the disease risk is conferred by the genes versus the environment or just random events).
Twin studies offer a very interesting window into human genetics and can often be extremely thought-provoking. Here at DNA and You, I will periodically point out an interesting twin study as food for thought.
For example, it is commonly assumed that any familial effect on political party choice is environmental in nature, but these authors set out to look into this in further detail. Basically the results suggest that although there is a modest effect of genetics on political party choice, this is probably conferred through intermediate genetic influences on attitudes about key political debates and other things like church attendance and social class.
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