August 8, 2017
"It's so predictable that it's stunning," she says. "You put that doll in the mother's arms, and the kid goes, 'Hey!' The first thing he does is run over there and say, 'Hey, what about me?' And then some of them protest. But the initial response – it's almost like they all went to the UN and decided together: you see a rival, you bolt; you hop on that lap; you stake out your territory."
Hart is a professor of human development and family studies at Texas Tech University, where she researches the relationships of infants and young children with parents and siblings.
Infants are hardwired to demand exclusive treatment from their mothers, she says. Through human evolution, babies needed access to their mothers' breast milk for at least the first two years of life, or they would probably die. The birth of a younger sibling for an infant was literally a mortal threat, and in that context freaking out a little is pretty understandable.