It’s 49% nature, 51% nurture

Twins studies have been so popular that one 2015 meta-analysis found that researchers had looked at no fewer than

17,800 traits — including depression, cardiovascular disease and gun ownership — involving more than 14.5 million twin pairs over the past 50 years. It concluded that both “nature” (what you’re born with) and “nurture” (what you’ve been exposed to as you age) are nearly equally important for understanding people’s personalities and health: The variation for traits and diseases was, on an average, 49 per cent attributable to genes and 51 per cent to environment.

But Nancy Segal, a psychologist at California State University, Fullerton, has another view. “A strict dichotomy between genes and environment is no longer relevant; they work in concert,” she said. “It’s trait-specific,” with different ratios depending on the characteristic in question. “In an individual person, the contributions of genes and the environment are inestimable,” Segal said.