Pure Pedantry

I have posted before about how I think that the role of genetics, at least in popular culture, has been overemphasized. Rather, the really interesting and important parts of genetics are the ways in which your genes interact with environmental factors.

There is an excellent article in the NY Times today about how longevity has a lot less to do with genes than people think. To wit:

The scientific view of what determines a life span or how a person ages has swung back and forth. First, a couple of decades ago, the emphasis was on environment, eating right, exercising, getting good medical care. Then the view switched to genes, the idea that you either inherit the right combination of genes that will let you eat fatty steaks and smoke cigars and live to be 100 or you do not. And the notion has stuck, so that these days, many people point to an ancestor or two who lived a long life and assume they have a genetic gift for longevity.

But recent studies find that genes may not be so important in determining how long someone will live and whether a person will get some diseases — except, perhaps, in some exceptionally long-lived families. That means it is generally impossible to predict how long a person will live based on how long the person’s relatives lived.

Life spans, says James W. Vaupel, who directs the Laboratory of Survival and Longevity at the Max Planck Institute for Demographic Research in Rostock, Germany, are nothing like a trait like height, which is strongly inherited.

“How tall your parents are compared to the average height explains 80 to 90 percent of how tall you are compared to the average person,” Dr. Vaupel said. But “only 3 percent of how long you live compared to the average person can be explained by how long your parents lived.”

“You really learn very little about your own life span from your parents’ life spans,” Dr. Vaupel said. “That’s what the evidence shows. Even twins, identical twins, die at different times.” On average, he said, more than 10 years apart.

The likely reason is that life span is determined by such a complex mix of events that there is no accurate predicting for individuals. The factors include genetic predispositions, disease, nutrition, a woman’s health during pregnancy, subtle injuries and accidents and simply chance events, like a randomly occurring mutation in a gene of a cell that ultimately leads to cancer. (Emphasis mine.)

The 3% value I think might be a typo because most research I have read suggests that the real value is around 30%. (Chart is from a review here.)

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A value around 20-30% is also what is suggested by a review by the person quoted. That review is Vaupel et al. in Nature Reviews Neuroscience:

Twin studies have consistently found that for cohorts born around 100 years ago, approximately 25% of the variation in lifespan is caused by genetic difference. Recent combined analyses of approx 20,000 twins born in Nordic countries between 1870 and 1910 confirm this, but they also show that the genetic influences on lifespan are minimal before the age of 60 and only increase after that age. This finding provides support for the search for genes that affect longevity in humans, especially at advanced ages. The results are comparable in the various Nordic countries, but other settings lack similar data to provide heritability estimates. Countries with larger socio-economic differences might be expected to have lower heritability estimates owing to larger environmental variance. (Citations removed.)

However, this mild discrepancy should not distract you from what I consider the still very reasonable take home. Longevity has just as much to do with environment as it does with genetics.

Genetics definitely plays a role. In fact, the Vaupel review actually has this lovely table of genes that have been implicated in longevity in a variety of populations (click to enlarge):

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These genes include cardiovascular, metabolic, immune system, and mitochondrial genes as well as genes that code for premature aging and telomere length.

However, I think that the take home is that the popular conception that your parents confered upon you a longevity destiny is inaccurate at best.

Anyway, read the whole NYTimes article, and for the initiated the Vaupel review is a good summary of recent advances in genetics.

Comments

  1. #1 suirauqa
    August 31, 2006

    Great post! That 20-30% dependence on genetics is actually quite understandable, as I think you’d agree, Jake. Even if one discounts (for the sake of discussion) the contribution of the environment, this is true for any polygenic character. If one defines longevity simply as the number of life-years, or perhaps health-years, inheritance of the right combination of genes that provide optimal functioning of cardiovascular, metabolism, and immune system automatically translates to long, healthy life, doesn’t it? The caveat is, again a factor that is ill-understood and oft-ignored in popular culture, that the ‘optimal functioning’ of any of these systems in turn depends on too many different processes, pathways and regulations, so that a measure of randomness of the outcome cannot be eliminated. Therefore, I think I like your last ‘take-home’ the best!

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