Why do some people get good results from their medical check-ups while the others don’t despite having the same life habits? Why are some people prone to depression while others tend to view life in a positive light? Why do some people have exceptionally good physical characteristics? Why do some people buy on impulse while others hold on tight to their purse strings? How much does an individual’s physical predisposition (in other words, genetic makeup) affect these things? Can this predisposition be changed through one’s own efforts? Twin research, or research conducted on twins, is a method for answering these questions.

Twin research is a research method that developed on the basis on medicine, psychology and behavioral science and is currently the focus of attention around the world. Even monozygotic (or identical) twins who share the exact same genes will respectively develop differences in the way these genes are expressed, and by the time they reach advanced age significant differences in their behavior and health will become apparent. Twin research enables us to find out in a detailed and precise manner how different environments and lifestyles affect health.