Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, September 14, 1995 TAG: 9509140036
SECTION: EXTRA PAGE: 3 EDITION: METRO
SOURCE: JOEL ACHENBACH
DATELINE: LENGTH: Medium
A: For the sake of others, you really shouldn't even try to live beyond the age of 112. Everyone who's ever had an aging parent has come to dread the phase known as ``the terrible one-hundred and thirteens.''
All species seem to have a maximum life span. Sea tortoises live to 150, and mayflies can barely get through a day.
For humans, the maximum life span hasn't changed even with all the advances in medical technology. Of the many thousands of centenarians, only a few have ever seen the far side of 115. The authenticated record was 120 years and 237 days, reached by Shigechiyo Izumi of Japan, who was born in 1865 and died in 1986. The Guiness Book of World Records reports that actuaries estimate that only 1 out of 2.1 billion people will live to the age of 115.
So what stops someone from just beating the odds and living to 150?
To start with, we'll give a statistical answer. Hardly anyone lives beyond 115 because so few live beyond 100. So few live beyond 100 because, on average, people only live to be in their 60s or 70s (it varies by sex and culture). Life spans follow a bell curve. People don't live to 150 for the same reason no one has ever run the 100 meters in 8 seconds - it's hard enough to do it in 10.
Next we go to the real issue: What's killing people? Are people just dying of ``old age''?
Of course not. Old age isn't a disease. It's not even clear when ``old age'' begins. (We would suggest it's when you start having elaborate dreams about shredded wheat.)
It is true, however, that over time our bodies become rather beat up at the molecular level by ``free oxygen radicals.'' These are charged particles roaming around and smashing into things, literally scuffing up the cells and sometimes causing cellular failure, mutations, etc.
But you could argue that the free oxygen radicals are no different from other environmental hazards that imperil us, such as bacteria and viruses. The body has natural defenses against all these things. For living pathogens we have antibodies; for oxygen radicals we have special scavenger enzymes that patrol our body looking for oxygen radicals. The scavengers, when they collide with oxygen radicals, turn them into harmless water.
The real answer to why we don't live longer is one that should be familiar to you if you have faithfully read this column every week since its inception (during, if we're not mistaken, the Harding administration): Natural selection is blind to the cares and concerns of the old.
Natural selection operates in breeding populations. Millions of years of evolution have given you a great body when you are 14 years old. To the extent that you live many more decades, you're basically just exploiting the residual excellence of your younger body.
At 34 you'll be coasting along nicely, says Michael Rose, a biologist and author of ``Evolutionary Biology of Aging.'' But he adds, ``When you are 54 you will be in the midst of a spectacular deterioration.''
He likens the process to a bank account. When you are a teen-ager and a young adult, the forces of natural selection will have already deposited into your account huge sums of money. But the deposits then stop. You can live off the money for decades but it eventually runs out.
Take those oxygen radical scavengers. (Please.) They do a great job keeping young people looking fresh. But the body doesn't generate so many as to prevent the gradual decay of the body in old age - because how would a young body know what it would be like to be old and wrinkled and slowly deteriorating? A teen-ager doesn't grasp mortality. Teenagers think they can smoke without getting cancer - and they can! For a while at least.
Natural selection has the same attitude. It doesn't pay attention to older people, because it barely knows they exist. Older people have stopped contributing biological information into the genetic pool. Therefore, people have no specialized defenses against common old-age ailments like cancer and heart attacks.
We shouldn't complain, though, since animals as a rule die by being eaten. Your basic gazelle gets a little long in the tooth, a little soft around the middle, and suddenly it's lion chow.
- Washington Post Writers Group
by CNB