Why Your Sibling's So Different Three theories By Kevin Spak, Newser Staff Posted Nov 28, 2010 6:27 PM CST 8 comments Comments They may look similar, but ... (Shutterstock) (Newser) – You share a set of genes. You grew up in the same place, around the same family. So why aren’t you and your siblings at all alike? Researchers have long puzzled over the question of why brothers and sisters can wind up so different, and NPR tracks down three theories: The Darwin Theory: Evolution was driven, some theorize, by competition, with organisms specializing so they didn’t compete directly. Siblings may do the same thing, taking on different roles to less directly compete for their parents time and attention. The ‘Different Family’ Theory: Others say that experiencing family events at disparate ages drastically changes how you perceive them. And since parents rarely treat all children the same, siblings aren’t actually being raised in the same environment at all. The Hyperbole Theory: Finally, some theorize that families are “comparison machines.” Even small differences between siblings become defining. A child who’s even a little less social than their sibling, for example, might be labeled “the introvert,” and slowly grow into the label.