The premise of Ms. Komisar’s book—backed by research in psychology, neuroscience and epigenetics—is that “mothers are biologically necessary for babies,” and not only for the obvious reasons of pregnancy and birth. “Babies are much more neurologically fragile than we’ve ever understood,” Ms. Komisar says. She cites the view of one neuroscientist, Nim Tottenham of Columbia University, “that babies are born without a central nervous system” and “mothers are the central nervous system to babies,” especially for the first nine months after birth. What does that mean? “Every time a mother comforts a baby in distress, she’s actually regulating that baby’s...