It has been suggested that twin studies are no longer necessary in the era of molecular genetics. The argument is that there is no longer any need to infer genetic influence now that we can directly measure genotypes. However, studies of latent genetic influence (as inferred from family, adoption, and twin studies) and studies of measured genotypes actually yield very different information and have complementary strengths and weaknesses, as has been nicely reviewed by my colleague Kenneth Kendler in previous papers (Kendler 2005, 2010). Information about aggregate genetic risk, as yielded by twin studies, gives us an idea of the big picture. It is essentially a satellite picture, providing an overview of the general landscape. On the other hand, molecular genetics offers a level of detail about the underlying biology that twin studies cannot. The corresponding metaphor would be the photographer on the ground who is taking pictures of the individual rocks and trees. But lost in that level of detail is information about the overall picture.
