Genetic researchers argue that genetic predisposition can partly explain depression. One of the main ways to investigate is through twin studies. In one of the largest studies to date, Kendler et al (2006) used 42,161 twins from the Swedish Twin Registry. They found that the concordance rate for female MZ twins was 44%, while for female DZ twins, only 16%. In male MZ twins, the rate was 31% and for male DZ twins, the...