On Nature vs. Nurture

First published 13 November 2016 · revised August 2026 with the evidence that has accumulated since, some of which sharpened the argument and some of which corrected it.

I have always found the interplay between nature and nurture interesting, and the polarised ways people understand it even more so. Let me illustrate with my own experience, because I have held both positions in turn.

Nurture is supreme — or so I thought

I began my professional life with a strong bias toward nurture: the belief that most people can achieve good physical and emotional health through safe, healthy choices made daily.

I still remember the first time I got hold of a book promoting healthy eating, exercise, fresh air and stress control. It was a paperback called NEWSTART. An Austrian physician gave it to a physician friend of mine during a visit to Romania, and because my friend did not read English, he passed it to me. I read it in a day. It felt like a revelation with every page.

I was in my first year of medical school, and I decided my calling was to teach people how much better life could be with good daily choices. I was one hundred percent confident that anyone, at any age, whatever their genes, could have vibrant health simply by practising good habits.

Shortly after finishing medical school I was employed part-time to lead the health department of my church in Romania. For almost eight years I wrote health articles for the church magazine, spoke in local churches about what daily choices could unlock, organised conferences for health professionals, and met a great many interesting people from one end of the health spectrum to the other. During most of those eight years I was also completing a five-year residency, presenting a weekly hour-long live health programme on Romanian public radio and another on the church station in the capital, and latterly helping run a church-operated medical centre in Bucharest.

My days started very early and ended very late. I hardly had time to eat, and when I did there was little to choose from — there were no vegetarian options for eating out in Bucharest then. Sometimes I wonder how I kept going on so little food with so much to do. I was burning the candle at both ends and there was not much left of me. By the end of that period I weighed around 115 lbs, at 5′8″.

Time for a change

Fast forward fifteen years. I moved to the United States, completed a master’s in human nutrition and a residency in internal medicine, and we were blessed with two children. I also gained over 40 lbs, most of it in the first year or so — which was its own education in how quickly environment overrides intention.

From 2007 I practised as a physician, seeing somewhere between three and four thousand patients a year, several of those years in a rural part of the Pacific Northwest. A significant number of my patients were Seventh-day Adventists who had been vegetarian for decades, who neither smoked nor drank, who exercised and attended church regularly.

It was a considerable privilege to watch the effect of that lifestyle at scale but one patient at a time. I think I now have a better sense of the real balance between nature and nurture. Here is what I concluded.

Long-term adherence pays off — in most cases

I have many patients in their eighties and nineties who look, move, talk and think a decade or two younger. Spending time with them is one of the pleasures of the job. I like their outlook, I like the stories they tell, and each of them is a testament to what healthy living does over a lifetime.

That impression is not merely mine. The Adventist Health Study-2 follows around 96,000 North American Adventists, and finds vegetarians with roughly 12% lower all-cause mortality than non-vegetarians, average BMI running from 28.8 in non-vegetarians down to 23.6 in vegans, and diabetes prevalence falling from 7.6% to 2.9% along the same gradient.¹² The patients I was seeing were, in effect, that study walking into my examination room.

And at the other end of the spectrum

I see an equally clear pattern of early physical ageing: wrinkled skin, degenerated joints and discs, obesity, diabetes, coronary disease, hypertension, and brain damage from strokes and vascular dementia.

A large share of the population grows up learning from those around them that life is not worth living without the “fun” of smoking, drinking and a host of similar habits. I sometimes ask such patients why they think they enjoy things that visibly damage them. I have never had a clear answer, beyond the occasional honest admission that bad habits are very hard to give up. I have had some memorable ones — a lifelong smoker once assured me that people will smoke in heaven.

But reality is not black and white

Between those poles sit most people, and there the interaction between genes and choices is intricate and sometimes surprising.

• A few patients seem born with such a strong constitution that despite what amounts to sustained abuse of their bodies, they reach their senior years in reasonable health. I have a delightful lady in her eighties who has eggs and bacon every morning and whose only real exercise is fishing a few times a month. She stands straight, thinks clearly, and is plainly enjoying herself.
• Conversely, I have seen many vegetarians and vegans with stubbornly elevated blood lipids. Most have an inherited alteration of lipid metabolism that keeps cholesterol or triglycerides above safe levels even on a diet containing no cholesterol and very little saturated fat. Do all of them have heart attacks? No. But I have seen several need stents, bypass surgery or carotid endarterectomy.

The most surprising lesson of my career has been how powerful genes are — taught to me, repeatedly, by patients whose best efforts were not enough.

What lifestyle can and cannot do

One of the more frustrating parts of practice is the near-daily encounter with patients convinced that any disease can be cured with lifestyle or supplements. I try to explain what I think should be obvious, and it comes down to sorting conditions into three groups.

Prevention and cure are different problems

A diet rich in fruit, vegetables, whole grains and nuts, with regular exercise and no smoking, prevents a substantial share of cancer. But once cancer has developed, it is not realistic to expect those same changes to cure it. Painting and caring for your car prevents rust; painting over rust that has already eaten the metal accomplishes nothing.

Here I need to correct my own 2016 text. I wrote then that “at least two thirds of all cancers” are attributable largely to poor diet and smoking. That figure was too high and I should not have used it. The careful estimate is that around 40% of cancer cases in US adults are attributable to modifiable risk factors, with smoking the largest single contributor at about 19% of cases, followed by excess body weight and alcohol.⁴

Forty percent is still an enormous number — roughly two in five cancers that need not have happened. It does not need inflating, and inflating it hands ammunition to people looking for a reason to dismiss the whole argument.

The part I got wrong in the other direction

Having spent this article arguing that genes are more powerful than my younger self believed, honesty requires the counterweight, because the evidence moved here too.

Family studies long suggested the heritability of human lifespan was somewhere around 15–30%. Then researchers analysed pedigrees containing hundreds of millions of people and found those estimates were substantially inflated by assortative mating — people tend to pair with partners who resemble them in background, education and circumstance, and that shared environment had been miscounted as shared genetics. The corrected figure for the heritability of longevity is under 10%.⁵

So both things are true, and they are not in conflict. Genes are decisive for particular conditions and comparatively weak for overall lifespan. Familial hypercholesterolaemia will not yield to diet. But how long you live, taken across a whole population, is mostly not written in advance.

A conclusion of sorts

It was not long after I started seeing patients that I had to put aside the idea that we are all born with roughly equal abilities. Some people arrive with bodies or minds so vulnerable that despite their best efforts they are plagued by ailments. I owe many of my eye-opening moments to that group. I have learned to expect, and to respect, what nature deals out.

But even there, a positive outlook goes a long way.

I remember a couple in their late seventies who had been through a great deal. They told me once how the husband, who had trouble with balance, fell one evening beside his bed and could not get up. His wife was in the room but too hard of hearing to catch the thud or his calls for help, and she was in her wheelchair facing the other way, reading. Desperate, he found a hairbrush on the floor near where he had fallen, and threw it at her. He said he had been nervous about doing it. I asked whether he was afraid of hurting her. No, he said — he was nervous he would miss.

He did not miss, and he did not hurt her. She realised what had happened and called for help.

Sitting in the examination room listening to them take turns telling this tragicomic story, laughing heartily throughout, I had something like an epiphany. These were two very happy people using humour and outlook to transcend obvious and severe health problems. In the end it matters more how we handle what we have than what we were given. Or as a church sign in our town once put it: do not let the things you cannot do stop you doing the things you can.

I used to think that was a sentiment rather than a finding. It appears to be both. In two cohorts followed for ten and thirty years, the most optimistic participants lived 11–15% longer and were considerably more likely to reach 85 — independently of income, health conditions, depression, smoking, diet and drinking.⁶ Association is not proof of cause, and no one should be told their outlook is why they are ill. But that couple were not simply coping well. They were, on the evidence, doing something that works.