February 16, 2004

Why Do We Live So Long?

The January 22, 2004 "Is Aging a Disease?" debate (the webcast and transcript are here) covered so much ground that I could write a dozen posts discussing points made by both sides. I doubt I'll get around to that (the next Sage Crossroads debate is this Thursday at 10:00 a.m.). But I thought I'd discuss a point raised by Dr. Moody regarding why we live as long as we do.

Some people have said that aging and death are nature's way of clearing the way for the next generation. Dr. Moody argued that this view is not scientific. It appears that evolution within our environmental niche has much to do with our life span, but through omission - not commission. Evolution is simply "unconcerned" with what happens to us after a certain age.

The wonder is that we don't die sooner. If we lived only to age 45 we'd still have plenty of time to reproduce and nurture our offspring. Generally an animal's body size is a good predictor of life span. The bigger the animal, the longer the life. Humans, however, live a life far longer than our body size would suggest. Few animals of any size live longer.

Dr. Moody mentioned one explanation for why we live longer: "The Grandmother" hypothesis. This hypothesis states that there was evolutionary pressure to design us to live beyond 45 so that we could help nurture the second generation into its reproductive years.

I think there is something to this hypothesis. Human children are uniquely defenseless in the wild. If Dad is miles away hunting and Mom is out of earshot gathering, Mammaw and Pappaw are quite valuable. Aunts and Uncles are better employed having kids of their own. And by having babysitters Junior has a better chance of surviving to pass on genes that, incidentally, favor longevity.

Additionally, the human mind is much more complex than that of any other animal. It takes many years for the mind to mature. It is physically possible for humans to have children years before they are emotionally and mentally mature. This creates further pressure for grandparents to be around to help with the second generation.

Whatever evolutionary pressure there may have been favoring grandparents, that pressure is less for great grandparents. Dr. Moody's point was that senescence is the product of evolutionary neglect (a lack of pressure to live longer), not part of some grand design to clear the way for future generations. Generally a child is not placed at risk by a great-grandparent's death, but there is no benefit conferred to the child by the death either.

If the only reason that we don't live longer is nature's neglect, there is no particular reason why we shouldn't, if we choose, solve the problem ourselves.

Posted by Stephen Gordon at February 16, 2004 01:56 PM | TrackBack

I've been procrastinating myself about writing an analysis of that debate - there is just far too much there to do it justice in the time I've had to spare.

Founder, Longevity Meme

Posted by: Reason at February 16, 2004 05:31 PM

What about: individuals with longer living parents and grandparents have a competitive edge due to the amounts of cultural data available and time for that to be transferred?

Posted by: John Farren at February 17, 2004 06:40 AM


Good point. Wisdom transfer time.

I can just see some poor family dying of thirst and hunger during a drought when Grandpa speaks up and says, "This same thing happened when I was a kid. My Dad led us on a five day march to the east where we camped out on a lake at the base of a mountain."


Posted by: Stephen at February 17, 2004 07:53 AM

The question seems to be "why do we want to live?" instead of "why do we eventually die?" since our ability to live longer is directly related to our ability and desire to keep ourselves alive. This may be due to natural selection, but what of the massive cultural influences on people's desire to live that have nothing to do with their natural inclinations. How else do you explain people willingly strapping bombs to their chests and walking into crowded bars. I think different cultures value life (and longevity of life)in so many different ways, that to say our lifespan is controlled by natural evolutionary levers is to stop short of the infinitely complex capacity of the human mind.

Posted by: blacknail at February 17, 2004 11:56 AM

Hey, Blacknail

You wrote:

...our ability to live longer is directly related to our ability and desire to keep ourselves alive.

Good point. That desire has always been there for some. Think of the Chinese Emperors eating bugs and all kinds of other weird things trying to find the secret of longevity. Those guys knew that death sucks and were at least trying to find an alternative. Others have taken the Leon Kass approach of believing that there's something beautiful and poetic about the fact that life eventually comes to an end. Still others embrace their death gladly, believing that they're on their way to some higher level of existence.

Most people probably start out thinking like the Chinese emperors, but they adopt the Kass approach out of frustration and resignation. The people willing to strap bombs to their chest are a tiny freakazoid minority.

I think you hit the nail on the head: when you couple the desire to live longer with the ability to do so, we can expect to see major changes in attitude towards death. That is, a lot of people who currently embrace the "beauty" and "grandeur" of death will start to have second thoughts.

However, I doubt that any developments in life extension will slow down the suicidal fanatics.

Posted by: Phil Bowermaster at February 17, 2004 12:21 PM

Kamikaze is, I suppose, part of a grand selection process, removing from the gene pool those that think it's a good idea or are suceptible to its wiles. I guess I bring it up only as an example of cultural influences. However, I actually think these things are all around us, driving us to conclusions that don't make sense.

For example, if you take a look at corporate culture, there is the old guard vs new turks thing, a tension that companies either thrive on or whither from. Here is a culture that basically has no use for it's participants after a certain age (either physical or mental). The result is a population of workers realizing that their value to pass on their sage wisdom has even expired, since it's that very wisdom that is driving the company into the ground.

It can all be boiled down to natural selection again: corporate culture doesn't care what happens to you after you've stopped being useful. At times, it feels that there is very little to hold on to. Really, why go on? But we do.

And perhaps the reason to go on is because we hate being controlled or told what to do. And maybe my own cultural influences are burning through now, but I think we as humans just hate losing, we love freedom, and we will do anything to keep ourselves alive for it. It's only when we resign ourselves as victims and lack the control to do anything about it, that we welcome life's end.

Posted by: backnail at February 17, 2004 02:02 PM


You've reminded me of an old joke:

A preacher asks his congregation for a show of hands from those who want to go to heaven. The preacher sees that everyone has a hand raised except Mr. Johnson.

"Mr. Johnson, don't you want to go to heaven?" he asks.

"Well yes, of course... I thought you were getting up a group to go today."

Those who argue against life extension from the Dr. Kass perspective sometimes ask something like "who really want to live to be 130?"

Answer: You will when you're 129 but feel 20.

Posted by: Stephen Gordon at February 17, 2004 02:34 PM

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