Scientists have already established that the hormone oxytocin is a trigger for love and affection. Now they have discovered that babies raised for their first two years in orphanages do not produce the same levels of oxytocin as children raised by their biological parents.

In a test designed to elicit cuddling and affection, Seth D. Pollak and his colleagues at the University of Wisconsin–Madison recruited 18 toddlers adopted from places such as Russia and Romania and an equal number of children with biological parents. Each toddler sat on his or her mother's lap while playing an interactive game with instructions such as “tickle your partner's tummy” and “hug your partner.” The children completed the same game on the lap of a friendly female stranger. The biological children showed a rise in oxytocin after playing with their own mother but not after playing with the female stranger. Yet the adopted children showed no rise in either case.

Pollak does not want to alarm would-be adoptive parents but wants to inform the early childhood field so that measures can be found to help adopted children bond early on. “These are children who start their lives in some very horrendous conditions, and within a day, their world changes,” Pollak says. “It may be that the child's comfort system isn’t kicking in.” Psychiatry professor C. Sue Carter of the University of Illinois at Chicago says there are ways to improve bonding, adding that hormones “are not destiny.”