Dr. Bruce Perry talks about the importance of social stimulation when a child is young.

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Dr. Perry has treated children who've survived genocides, as well as boys and girls raised in closets and cages. These obvious incidents of trauma and neglect can alter young lives forever. In homes across the country, however, Dr. Perry says parents may be stunting their child's development unintentionally.

"Our modern world is very different than the world that our brain is engineered for. In the world that human beings have lived in for centuries, there were many, many, many more people in our lives—aunties, grannies, extended family. We were in continuous relational interaction with each other," he says. "The developing child under the age of 6 had at least, in those typical settings, four developmentally mature individuals who would help protect, enrich and nurture these kids."

Thanks to the loving attention of many family members, Dr. Perry says the part of the brain involved in relational interaction got lots of stimulation. This helped people grow up with a tremendous sense of empathy.

Over the years, things have changed. "In the modern world, we have childcare settings where there's one adult and eight, nine, 10 kids," he says. "Then, in a home, you've got a poor, isolated mother who's got multiple children."

The consequence isn't what Dr. Perry would call neglect. "I would say that it is underdevelopment of a potential," he says. "Broadly, we are underexpressing the potential of our children to be humane. ... We aren't providing equal amounts of social, relational and emotional experiences to help them be compassionate."