What Twins Can Teach Us About Nature vs. Nurture

The day my identical twin boys were delivered by an emergency cesarean, I noticed a behavioral difference. Twin A, who had been pushed against an unyielding pelvis for several hours, spent most of his first day alert and looking around, while Twin B, who had been spared this pre-birth stress, slept calmly like a typical newborn.

My husband and I did our best to treat them equally, but Twin A was more of a challenge to hold — we called him “our lobster baby” — while Twin B was easily cuddled. As the boys developed, we saw other differences. Twin B rehearsed all the ambulatory milestones — crawling, walking, cycling, skating, etc. — while his twin watched, then copied the skill when it was mastered.

Although they shared all their genes and grew up with the same adoring parents, clearly there were differences in these boys that had been influenced by other factors in their environment, both prenatal and postnatal.

The relative importance of nature and nurture to how a child develops has been debated by philosophers and psychologists for centuries, and has had strong — and sometimes misguided — influences on public policy.