For years, I accepted the conventional wisdom that genetics accounts for less than 30% of human lifespan. I never really questioned that figure, and in retrospect, that’s a little embarrassing. But I was hardly alone. Those numbers were widely repeated, rarely examined, and neatly aligned with a popular narrative: that lifestyle choices largely determine our fate. This narrative has been further amplified by “longevity influencers,” many of whom build businesses around lifestyle prescriptions often coupled with products and services they sell.

Recent Twin Study sheds new light on the role of genetics in determining longevity

A newer large-scale twin study suggests that genetics plays a much larger role, closer to 50%, in determining lifespan. What struck me was not just the revised estimate, but why earlier studies were likely misleading. Many failed to adequately account for deaths from causes unrelated to either genetics or lifestyle, accidents, wars, epidemics, and other random events. Including those outcomes diluted the biological signal. This was not malicious science, but it was methodologically weak science.

This raised a deeper and very personal question for me: does the relative importance of genetics and lifestyle remain constant throughout life? Intuitively, it shouldn’t. The same behavior can affect people very differently depending on their genetic makeup. Smoking is a clear example. Roughly 30% of long-term smokers develop lung cancer, while most do not. Studies of identical twins show significantly higher concordance for lung cancer among smokers than is seen in fraternal twins, indicating that both lifestyle and genetics play essential roles. 

The role of Genetics increases as we age

We die young from bad luck and bad choices; we die old from biological limits and those limits are largely genetic. We would not die from smoking if we did not smoke.  So lung cancer can be largely avoided by life style.  It is complicated because genetics will play a major role at any age in determining the propensity of getting cancer from smoking. Genetics plays a role continuously as we age but that role increased later in life.

What this means for me personally

At 81, this is no longer an abstract discussion for me. Some people, if given the choice, would prefer not to know how long they might live. I am not one of them. I operate under the assumption that I have at least another ten years of healthy life ahead of me, and I make plans accordingly. That assumption is not blind optimism; it is informed by family history. I come from a long-lived family, with many direct ancestors living well into their nineties. In that sense, I won a genetic lottery.

Genetics also matters in subtler ways. It influences not only how long we live, but how we live. It shapes temperament, risk tolerance, impulse control, susceptibility to addiction, and even how rewarding or punishing certain behaviors feel. In this way, genetics indirectly influences lifestyle itself, nudging some people toward healthier patterns and others toward less healthy ones.

Personalized Longevity

All of this leads me to a firm conviction: longevity advice must be personalized. It is easy to generate a list of twenty things people “should” do to live longer and live better. The problem is not that such lists are wrong; it is that no one will do all twenty. Within them are usually two or three high‑leverage factors that matter far more for a given individual than the rest. Identifying those factors requires understanding family history, increasingly sophisticated genetic testing, and crucially, feedback mechanisms that show whether interventions are actually working.

You Are as Old as Your Oldest Part

Another idea I have found useful is this: you are as old as your oldest part. Our bodies do not age uniformly. Different systems decline at different rates. At 81, my cardiovascular system would be considered excellent even for a man half my age. My bladder, on the other hand, reminds me several times each night that I am not in my forties. This uneven aging is normal, but we rarely address it systematically.

We already do this selectively. We screen for colon cancer. We monitor heart disease risk. But we could—and should—go much further by assessing the biological age of individual subsystems: brain, heart, metabolic system, kidneys, and musculoskeletal function. The goal is not to chase perfection, but to identify weaknesses early and respond intelligently.

I strongly believe in preventive medicine that begins with routine testing and monitoring. We are only beginning to see the role AI will play in analyzing longitudinal medical data. By combining many blood tests over many years—true multivariate analysis—and integrating that data with genetic information, we are likely to gain insights that allow for much earlier intervention.

Advances in diagnostics will also play a major role. Liquid biopsies, which detect cancer-related DNA in the blood, and improvements in imaging are already changing what can be identified early. When potential problems with significant implications for longevity are detected sooner, meaningful interventions are often still possible.

Bio-Feedback Is Key

This is where wearables and continuous biofeedback will become increasingly important. They do not make us younger. What they do is make decline visible sooner. Visibility enables intervention, and intervention—when targeted and personalized—can meaningfully extend both lifespan and healthspan.

Longevity is not a simple contest between genetics and lifestyle. Their relative importance shifts over time. Genetics increasingly sets the boundaries as we age, but personalization restores agency within those boundaries. Understanding that balance may be one of the most important steps we can take toward living not just longer lives, but better ones.