“’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.’”
- - The New York Times, 31 August 2006
Many years ago, a friend was approaching his 40th birthday. He was convinced that because his father had died of a heart attack at age 42, his days too were numbered. I can report that, now in his late sixties, the man is still alive and healthy, but over the intervening years, I have met an astonishing number of men (much more so than women) who expect to die at about the age their father’s did.
According to several ongoing studies into longevity, reported in a remarkably thorough piece written by Gina Kolata in a recent issue of http://www.nytimes.com/2006/08/31/health/31age.html?ex=1314676800&en=7a042fdf09063881&ei=5090&partner=rssuserland&emc=rss, this is bunk. Dr. Kaare Christensen, a professor of epidemiology at the University of Southern Denmark has studied 10,251 pairs of identical, same-sex twins whose genes are identical, and fraternal twins who are no different genetically from ordinary siblings.
Even with identical twins, says Dr. Christensen, “the vast majority die years apart.”
“…there was almost no genetic influence on age of death before 60, suggesting that early death has a large random component – an auto accident, a fall. In fact, the studies of twins found almost no genetic influence on age of death even at older ages, except among people who live to be very old, the late 80s, the 90s or even 100.”
Dr. Caleb Finch, a researcher on aging at the University of South California, who reports that genetically identical animals living in the same environments die at different times, further defines randomness:
“There are two phases of randomness,” he says. “There’s the randomness of life experience. The unlucky ones, who get an infection, get hit on the head or get mutations that turn a cell into cancer. And there are random events in development…random differences in development early in life can set the stage for deterioration decades later.”
Even the belief that certain diseases are strongly inheritable is being refuted.
“…only a few cancers – breast, prostrate and colorectal – had a noticeable genetic component. And that was not much…”
“…Alzheimer’s is so common in the elderly that it occurs in 35 percent of people age 80 and older. If genes determine who gets Alzheimer’s at older ages, Dr. Pederson says, ‘those genes must be very common, have small effects and probably interact with the environment.’”
“Heart disease appears to be indiscriminate, striking almost everyone eventually…”
“…the general picture is consistent in study after study,” writes Ms. Kolata. “A strong family history of even a genetically linked disease does not guarantee a person will get it, and having no family history does not mean a person is protected.”
Matt McGue, a professor of psychology who studies life spans as contrasted with personalities says,
“I’ve been in this business a long while, and life span is probably one of the most weakly heritable traits I’ve ever studied.”
That certainly appears to knock the old joke, "I come from a line of long livers," into a cocked hat. It has been conventional wisdom all my life that if our parents and grandparents lived to a ripe old age, we too, especially with the improved nutrition and healthcare we have benefited from in the 20th century, can expect to live unto the outer reaches of human longevity.
Maybe, maybe not. But it appears to have little to do with our parents' longevity. This story is popular journalism at its best, reporting practical knowledge resulting from recent and ongoing genetic studies in language laymen can understand. It's worth reading.