In the past century, most developed nations have experienced large increases in mean life expectancy, starting from around 50 years to the current estimate around 75–80 years. This has been due to a marked reduction in early life mortality during the first half of the twentieth century, followed by a less recognized almost twofold reduction in mortality at ages above 70 in the past 50 years.
When confronted with such statistics, most people are apt to attribute the changes to good genes. This has been so especially when people have recognized the phenomenon known as ‘longevity hot spots’ – areas on the globe (like Okinawa in Japan) where people seem to live way beyond a century. Population studies however debunk such misconceptions. Japanese Okinawans who probably enjoy the longest lifespan on the planet adopt the mortality patterns of the countries they emigrate to when they abandon their traditional Okinawan ways and adopt the lifestyle of their new places of abode. Their genes did not change; their environment and lifestyle did!

Human family studies have indicated that a modest amount of the overall variation in adult lifespan (approximately 20-30%) is accounted for by genetic factors. In 1996, Herskind and colleagues of the Centre for Health and Social Policy, Odense University, explored the heritability of human longevity in a population-based study of 2872 Danish twin pairs born 1870-1900. They concluded after analyzing their results that the heritability of longevity was 0.26 for males and 0.23 for females. Longevity thus seems to be only moderately heritable. But how important is this heritability from birth? Christensen and colleagues from the same Odense University in Denmark studied Finnish and Swedish twins born between 1870 and 1910 comprising 20,502 individuals who were followed until 2003–2004. Their conclusion?... Genetic influences on lifespan are minimal prior to age 60 but increase thereafter.
Now I would have thought that deaths at young ages would reflect things like inherited predispositions to premature heart disease or to fatal cancers or to illnesses such as sickle cell disease. But that is not borne out by the scientific evidence. If you are hoping that you have inherited a couple of good genes from your ancestors because they lived long, it appears you have a long wait before you can cash your inheritance – the genetic factor does not kick in until you are past 60 years old! In fact the Christensen paper reported in Human Genetics 2006 (Genetic influence on human lifespan and longevity) found almost no genetic influence on age of death even at older ages, except among people who live to the late 80’s and beyond. Since reading their report I have come to think of the heritability of longevity as a post-dated cheque, valid only on your deathbed!
If you are going to live long and not regret it, you have to look elsewhere, certainly beyond your genes.