The scary phenomenon of escalating family resemblances

Research shows that you really are turning into your parents, writes Faye Flam.

WITH so many family gatherings at this time of year, many of us notice that our siblings are turning into our parents, and some of our partners’ and friends’ children are turning into their parents. That’s no illusion. As scientists have learned from ‘‘nature versus nurture’’ studies on twins and adoptees, humans become more like their biological parents and other family members as they get older.

This is a little scary. It’s not that we don’t love the anxious relative who can’t enjoy a holiday dinner because her stuffing wasn’t perfect. It’s just unnerving to realise they are reflections of the selves we might become.

I learned about escalating family resemblances from talking with Robert Plomin, a behavioural geneticist at the King’s College London. He describes the phenomenon in his recent book, Blueprint: How DNA Makes Us Who We Are. At first, I thought the interview might be contentious, considering that I’d recently written a column titled ‘‘You Are Not Your DNA’’.

It turned out we disagreed very little. He and I shared a fascination with families. His pioneering studies used families — following adopted children as well as their birth mothers. He found that children take after their birth mothers, but not their adoptive parents, in cognitive skills, interests and personality traits. And as they get older, the resemblance only got stronger.

He attributes this to the fact that people with literary, musical, mathematical or scientific inclinations will construct environments that amplify these predispositions; they are not necessarily or primarily products of those environments. He even found that adoptees resembled their birth mothers in such seemingly nongenetic traits as television watching and the likelihood of getting divorced. But then, these are influenced by personality traits. (Not that the traits associated with divorce are necessarily bad.)

The adoptive parents had surprisingly little influence on anything measurable. ‘‘Parents don’t have the levers to pull they think they do,’’ he said. Despite all the hype about tiger mums, teaching grit and 10,000 hours of practice, he said, the reality is that children are not blobs of clay you can mould.

This does not mean that we’re shaped only by nature. It’s just that people have misunderstood nurture. To Plomin, nurture is not how you were parented but the multitude of slings and arrows you encounter in your life. We are moulded by unpredictable forces, but the very nature of the clay is a mix of our ancestors.

Some reviewers have accused Plomin of being a genetic determinist — that is, putting too much emphasis on genes as the drivers of our futures. In the introduction to the book, he does indeed say that genetic testing could provide a sort of crystal ball.

But in our conversation, he said genetic tests (and family members) showed us a future that might be — not a future that must be. You might have a high risk of becoming an alcoholic, and knowing that might make you more conscious about avoiding this outcome.

Plomin has also studied twins and the similarities between monozygotic, or ‘‘identical’’, twins. They share almost identical DNA and usually look quite similar, but of course they are unique individuals. That was strikingly illustrated in the recently released documentary Three Identical Strangers, about monozygotic triplets separated in infancy and reunited at 19. The three young men looked alike, had the same smile and the same gestures, but (spoiler alert) one was much more troubled than the other two and eventually killed himself.

The filmmakers try to suggest that the adoptive father is to blame, though there was no convincing evidence that he did anything wrong. Reading Plomin’s book made me appreciate how brutally unfair this accusation may have been, and how dismissive of the influence of random slings and arrows.

Plomin is a great enthusiast for the newest generation of genetic tests, now capable of giving us information on traits that are influenced by a multitude of genes, including cognitive skills and personality traits. That might be considered an advance, as long as this information isn’t used against us — but there’s no guarantee it wouldn’t be used badly and stupidly by employers, teachers or people trying to sell us stuff we don’t need.

Even if I could get such results confidentially, there’s a limit to how much insight can be gleaned from various onedimensional scales of personality traits. There’s so much more richness in watching the way our parents and other relatives undermine their own happiness, or find it against the odds. They are not me, but they do share a good portion of DNA. We navigate around many of the same rocky shoals, but I imagine that if I’m careful, I can avoid running into them. Some of them.

But this might just be a personal preference for stories. I turn to science when I want to understand the natural world and trends in human behaviour. For wisdom on how to live, I find myself increasingly gravitating towards novels, stories and people. My mum was the same way.