The well-intentioned Head Start program, for example, was designed to give children from deprived environments an academic leg up. But it might have been more effective to teach their caregivers parenting and nurturing skills, as well as how to enrich the children’s environment and resist bad influences.

Children learn from what they see around them, and if what they mainly experience is violence, abuse, truancy and no expectations for success, their chances for a wholesome future are compromised from the start. As my son Erik Engquist, a fellow journalist who was Twin A, put it: “Genes define your potential, but your environment largely determines how you turn out. The few who escape negative influences are outliers.”

However, if the genetic potential is there, having even one loving, supportive adult in a child’s life can make a difference in how he or she grows up.

My sister-in-law Cindy Brody is a classic example. As she tells it, both her great-grandmother and grandmother escaped from abusive relationships and gave their children to family and friends to rear. Cindy’s mother ended up with two nurturing adoptive parents and she, in turn, nurtured and loved her two daughters. But her mother died when Cindy was only 8 years old, leaving her and her sister, she said, “with a cold, aggressive, shaming father who believed in corporal punishment” and remarried a woman with two sons who sexually attacked the girls.

Cindy fled home at 17, determined “not to let anyone hurt me ever again.” Buoyed by an inner strength and the nurturing, strength and independence fostered by the women in her life — her mother, grandmother and an aunt — Cindy said she was able to fend for herself, get a good job, live her dreams and be a nurturing, loving mother for her own son and daughter.