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Live Long OR Prosper

Life Extension enthusiasts (and I'm one) always talk about how short life is. But in a world where body size correlates closely with life span, we humans live a lot longer than we should expect. By that rule we should live about as long as pigs.

In his answer to the question "why do animals have different life spans?" Dr. James Goss of the University of Pittsburg listed several general rules.

1. Body size - the bigger the animal, the longer it lives.

2. Fecundity - the more offspring that an animal is capable of producing, the shorter it lives.

3. Brain size/body size ratio - the greater the ratio the longer the life.

There are other rules like "the longer the period between birth and sexual maturity, the longer the life." That seems a bit like saying "the longer the life, the longer the life." Actually, I think it's mostly a restatement of the fecundity principle. If it takes a long time to get ready to have babies, you are going to have fewer babies.

Also, there's the idea that the hazards of a species' environmental niche affects life span. If you are vulnerable, you'll tend to have a shorter maximum life span. I think this is related again to both body size and fecundity. If you are small, you tend to be more vulnerable. If you are vulnerable, it pays to have many kids early to insure that a few of those kids survive to reproduce.

We humans break the body size rule pretty badly, but that's made up for with these other principles. We don't usually have litters (absent the intervention of reproductive medicine). About the time other animals our size are dropping dead, we start having a few kids. Family sizes are smaller today than in times past, but we have always had fewer kids than most animals our size, so its natural that we'd spend more time on each child.

But human children require an extraordinary amount of care because humans depend more on transferred knowledge and less on instinct than other animals. This may tie in with the brain size/body size ratio rule, but I would think that the more a species depends on instinct, the shorter its life.

Why? Because there's no need for wisdom transfer time. A salmon can reproduce and drop dead. He doesn't have to teach his offspring how to swim upstream (I was going to say "they have schools for that" but thought better of it. You're welcome). It just comes natural.

The better an animal is able to convey it's wisdom, the more its offspring will benefit from wisdom transfer time. My guess: the advent of language saw a quick lengthening in human life span. If you are able to transfer survival wisdom to your offspring, then it pays, from a evolutionary point of view, to live a long life.

In the past those who were fortunate enough to have parents and grandparents warning them of particular dangers were marginally more successful at surviving to reproduce. That created evolutionary pressure to live longer.

It wasn't until relatively recently that science accepted that life span was controlled by genetics. In 1993 Cynthia Kenyon discovered that strains of the nematode worm C. Elegans with a mutant daf-2 gene live twice as long as normal.

Why? We still don't have a complete answer, but a Massachusetts General Hospital team discovered that the daf-2 gene normally suppresses cellular waste management systems late in life. Instead of devoting resources to cleaning up the cells (which would mean longer life), the body devotes itself to reproduction.

The mutant daf-2 gene that Kenyon discovered doesn't suppress this cellular clean-up effort the same way. So organisms with this mutant daf-2 continue cleaning up the junk and, therefore, live much longer.

Individuals that damp down their garbage disposal systems and use the energy for reproduction gain a short-term competitive advantage over those that keep on detoxing. Of course, the price they pay is ageing more rapidly and dying younger, but on the whole natural selection couldn't care less what happens to an organism after it has reproduced.

The end result is that evolution has favored cells that opt out of the detox business and allow molecular detritus to pile up.

From an reproductive/evolutionary standpoint, there has always been tension between living long and prospering...reproductively. Within humans, there has already been evolutionary pressure to detox longer than with other animals - to grant wisdom transfer time. We prosper, in part, by living long. In a way it's recognition by nature that individual humans are special.

"Thanks nature, you've been kind." But even this "kindness" has a mercenary aspect. Individuals are imporant to nature because of what they can do to insure the survival of their genes (which in this case is the passing down of knowledge) not for who they are. Nature has also been cruel in that it has provided us the intelligence to contemplate our own demise.

Most mammals swim instinctually, but young apes and humans fear the water. It has been theorized that apes are smart enough to understand the concept of drowning, but are not usually smart enough to see past that fear to learn to swim.

Using our intelligence to postpone death will be no more unnatural than learning to swim, taming fire, or building flying machines. Its what we humans do...naturally.

NOTE: This post is a sequel to last year's "Why Do We Live So Long?" post.


Great stuff, Stephen.

I am struck by the juxtaposition of ideas in your last two paragraphs. I agree that, in a certain sense, the effort to extend life comes "naturally." But there is also a very strong sense that most of us have (and that many, if not most, will argue in defense of) that there is something supremely "unnatural" about trying to ward off death.

Maybe life extension advocates are the first wave of apes to suggest that, hey, perhaps we should give this "swimming" thing a try.

I guess my point is:

1. Humans are a product of nature. Whatever technology we come up with is, by definition, natural.

2. But, if life extension isn't natural, so what? Nature uniquely burdened us with brains big enough to understand the inevitability and implication of death. If we choose to use those big brains to postpone death, then why shouldn't we? That's just sweet irony.

To nature, intelligence was just another adaptation no different from webbed feet for a duck. But intelligence is unique. It's Pandora's box.

And we didn't open it.

Perhaps this line of thought is just silly. There's maybe little point in arguing over whether some technology is natural or not. Maybe the better question is "Is this the right thing to do?"

Life extension is the right thing to do because each death is a unique tragedy - the loss of an individual. If our society has to change to accommodate extremely long lives, then let it change. Society has been through upheavals over much less.

One thing about immortality as portrayed in the arts. You generally have to do something epic. Eg, become a vampire, god, set up some sort of empire or great machine, or some other bogus means. Ie, if billions of people have to die so that a person can live a bit longer (eg, this story) then of course, you are going to be reluctant to endorse immortality.

But if immortality just means that you need some sort of fancy checkup every six months, then what's the big deal?

Given the emotional aspect of human reproduction, I can make a claim that my notion that "live long and prosper" is a "pick any two" list would be on topic here. A study of the lives of succesful people also show a link between acting on one's longing and prospering.

As the husband of a geriatric nursing aid, I would point out to Stephen Gordon that extending drool time is not a worthwhile goal; it is only when we extend middle age that we are accomplishing something. See for example Aldous Huxley's "After Many A Summer Dies The Swan".


Exactly. You won't endanger your immortal soul to go get a check-up.

But, on the other hand, what institution would not be rocked by indefinite life? Our whole society is built on a life cycle model. We're born, grow and learn, work, get married (or, perhaps I should say, pair up), have children, work harder, retire, and die.

There's not one aspect of that cycle that wouldn't change. We would probably choose to physically mature just as quickly, but education might go much longer (Maybe not. With everything changing so quickly, perhaps students would just be taught to be lifelong scholars. Once they've grasped the importance of that, send students out and have them learn as they need to), people might be slower to settle down - they might live, as Leon Kass fears, a Seinfeld life for a long time.

Kids - who knows how that would go? Would people have more kids because their "child-bearing" years stretch on, or would they put off having kids indefinitely because they have the time? Probably there will be some of both, but it seems to me that the putting off model seems to be winning right now - and we don't even have life extension yet.

Will people look at marriage the same way? Some elderly people are no doubt bidding their time. Sure they're sick of the sight of their spouse, but why get divorced at age 80? "Truce! I'm too tired to fight anyway. Last one alive wins."

Cynical, but probably true for some. Others, no doubt, are very much in love after many years of marriage. If they were granted youth again, they'd stick together.

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