Map of life expectancy at birth from Global Education Project.

Monday, April 04, 2005

The Culture of Life Confronts Biology

To be honest with you, I still don't know what the heck "The Culture of Life" is supposed to mean. But whatever values the culture may uphold, they can only be implemented in the context of reality.

The evolutionary theory of longevity, which accurately explains everything we now know about aging and mortality, proposes that natural selection favors overall reproductive success. That means our lifespans are configured for the benefit of our offspring. Since we nurture our young and continue to cooperate with them in social groups after they have grown, there is some evolutionary benefit to continuing life after the reproductive phase is over. As old folks, we can be repositories of wisdom (or possibly of entrenched foolishness but let's hope for the best), babysit our grandchildren, knit comforters, or be Supreme Court Justices and Senators. But then as far as natural selection is concerned, it's time to get the heck out of the way and stop competing for resources with our grandchildren and great grandchildren. And anyway, evolutionary adaptations that favor our vigor and success during the reproductive years frequently turn out to be bad for us later on in life. (No moral principle is asserted here, just giving you the facts.)

In the last century, in the wealthy countries in particular, due principally to better nutrition and santitation, the isolation of humans from animal predators, less dangerous occupations, etc., we greatly reduced early mortality from environmental causes. Increases in average lifespan continued at a slower rate due to some continuing public health measures (everything from airbags to measles vaccine to nutritional fortification of refined flour), and to a lesser extent to medical intervention, which is very expensive per period of life gained.

The environmental and lifestyle improvements, with occasional help from an appendectomy or trauma care, can get us to senescence, but then the parts start to wear out. The joints degrade, the mitochondria become less efficient, the neurons die. Right now it looks like a person with the most favorable genetic makeup, optimal diet and lifestyle, good (expensive) medical care and good luck, can conceivably make it to 120 years old, but most people won't get near that. Eighty to 90 years is a more realistic hope for most of us. And then we have to hope as well that by medical intervention, we can "compress" the inevitable period of severe disability and cognitive decline into a short time before death, but so far that hasn't really happened. In fact, by extending life we've pushed more people into the realm of dementia, severe arthritis, cancer, and of course heart disease and diabetes. Those latter two may be largely preventable in principle, but we are far from having a social environment in which they will become less prevalent.

Now there is a movement -- disturbingly cult-like, although it is led by scientists -- of people who claim that the human lifespan can be greatly extended, that the average person might make it to 112 and that 120 would not be uncommon. I say cult-like because a lot of these people are True Believers, whose enthusiasm goes well beyond the evidence. But even if they are right, there are some serious problems with this proposal which they don't like to talk about. Let us suppose that by some very expensive interventions, we could maintain people's lives to an average of 112 years, and that by some additional, probably even more expensive interventions (joint replacement and more speculative technologies such as growing new organs from stem cells) we could keep at least a portion of them reasonably independent and capable. (Although no cure for Alzheimer's disease is yet in sight.) Resources, of course, will continue to be scarce. Some people in the wealthy countries will have access to these technologies, presumably, but it might cost more than the gross economic output of the planet to extend them to everybody. In any case, we would have to sacrifice a great deal for such interventions, including providing for basic needs of billions of younger people many of whom would never make it to the realm of life extension.

Without referring to any specific cases, what does this suggest about how we should think about medical intervention to keep people alive in general? Does it make sense to talk about the "sanctity" of human life, however we define human life (which is question #2 of course)? Is "life" the highest moral value? If not, why do so many people seem to think it is?

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