Research on the dangers of institutional care for young children dates back to the 1940s. For as long as they have existed, orphanages have always had alarmingly high death rates. From the early 20th century onwards, this was blamed on contagious disease–and so, attempts were made to keep orphanages sterile, to isolate children from each other by doing things like hanging sterilized sheets between their cribs.

But Austrian psychoanalyst and physician Rene Spitz proposed an alternate theory. He thought that infants in institutions suffered from lack of love–that they were missing important parental relationships, which in turn was hurting or even killing them.

To test his theory, he compared a group of infants raised in isolated hospital cribs with those raised in a prison by their own incarcerated mothers. If the germs from being locked up with lots of people were the problem, both groups of infants should have done equally poorly. In fact, the hospitalized kids should have done better, given the attempts made at imposing sterile conditions. If love mattered, however, the prisoners’ kids should prevail.

Love won: 37% of the infants kept in the bleak hospital ward died, but there were no deaths at all amongst the infants raised in the prison. The incarcerated babies grew more quickly, were larger and did better in every way Spitz could measure. The orphans who managed to survive the hospital, in contrast, were more likely to contract all types of illnesses. They were scrawny and showed obvious psychological, cognitive and behavioral problems.