...twins

"In the past several weeks Molly has been doing research into the phenomenon of twin-ness. She has found astonishing things, in some cases alarming things--one of them being that identical twins reared apart more closely resemble each other than twins raised in the same household!--for that reason that, when raised together, twins make a conscious effort to become individuals; there is something profoundly distatesful about being 'identical' to another person. When twins are raised apart, however, without knowing each other, each naturally follows the bent of his instinct--the genetic trajectory of what might be called destiny. Consequently some of the twins in the studies Molly has been reading resemble each other to an uncanny degree: they unknowingly marry people with the same names, have children at approximately the same times and give them similar names; their I.Q.'s remain near-identical through life, despite differing environments, as well as their medical ailments; their tastes in food, clothing, jewelry et al. are remarkably similar, as are their personality traits and mannerisms. And of course they look alike. And frequently mistaken for each other". (From Lives of the Twins, by Rosamond Smith).