stroke as a fitness advantage
Thursday, March 1 2007
I doubt humanity will linger in its present energy-sustained exuberance long enough for these conditions to shape us evolutionarily, but if we should be that lucky, today I had an entertaining thought about a trait we'd develop: instant death just prior to advanced old age.
To fully explore this idea, let me take a moment here to explain the current thinking (as presented by Jared Diamond in his book the Third Chimpanzee) as to why it is that people live as long as they do. In primitive non-literate societies, the elderly are the only repositories of tribal and familial wisdom. This oral tradition can save a village in unusual weather conditions, ones with which most people in the village have had no experience. It can also come in handy when rare resources are discovered and need to be exploited. Consequently, those tribes that tended to have a few old people in them tended to out-compete tribes that did not, and this is why our present society (people descendant from the most successful tribes) are stocked with people capable of living well beyond their reproductive years. Though they themselves can no longer produce offspring and directly spread their genetic information, their learned information confers survival advantage to other, younger people: descendants, extended family, and others in the tribe. Jared Diamond hypothesizes that menopause evolved to allow women to survive into their old age without having to take the risk of bearing children much past the age of forty. Sure, after menopause women could no longer produce children, but they can still devote considerable effort into increasing the survival advantages of the children they have already produced, as well as their grandchildren.
But in our modern world, one full of books and searchable web databases, the elderly confer fewer advantages on those in the society around them. While healthy grandparents can still lavish attention on their grandchildren and provide other such direct survival advantages, it is objectively difficult to see how a senile grandmother living out her final days in a nursing home is doing anything positive for her descendants. Indeed, the senile are a burden, spending down their accumulated savings and leaving their children worse off than those in society whose ancestors die quickly, before senility has had a chance to set in. Unlike other cultures, our society has an extremist position on the value of the elderly, believing their lives should be maintained as long as biology itself permits, and it is taboo to consider the ways in which this makes no sense. It's easy to imagine our society gradually losing competition with a society that doesn't so value its dying elderly. While we spend our money prolonging the unpleasant lives of those no longer making useful contributions, another society could take their analogous resources and devote them to education, research, health care, or the military. Indeed, tribal competition among Native Americans was such that some of the tribes surviving at the time of their first contact with Europeans had the custom of banishing their "decrepit" elderly to certain death in the wilderness.
But even if our society isn't conquered by one with a penchant for dispatching its senile grandparents, and even if it never changes its view of the value of its decrepit (and such cultural changes are unlikely), there's always the chance that some family lines within our society will out-compete other family lines due to genetically-borne predispositions to certain kinds of death. Menopause can, after all, be thought of as such a death (though, of course, it is the death of a function and not of an entire human). Among human women, onset of
menopause is remarkably consistent and is inevitable for those who live into their late fifties. If our society manages to continue as it presently exists for thousands of years, I can imagine the proliferation of family lines having a peculiar genetic predisposition: its members drop dead just before senility, thereby passing on accumulated wealth undiminished by end-of-life expenses. The mechanisms for such deaths are already present in our gene pool: genetically-linked predispositions to heart disease and stroke (with effects exaggerated, of course, by our unsustainable fondness for beef).
As I said at the beginning, however, I think it's doubtful human society will be able to maintain its existing oil-fueled exhuberance. We're on the steep rising side of a J-curve when it comes to all sorts of factors, and J-curves cannot be maintained forever (see dotcom bubble, the). For this reason, I don't anticipate a soft landing. When we've overshot our arable land and fuel supplies, there will be a crash followed by a prolonged dark age. Humans will survive, but most of humanity will revert to a non-literate state, one with poor health care, a barter-based economy, and a revived need for the non-senile elderly. At that point Darwinian forces will be similar to the grim ones that shaped the way we are today, and there will no longer be a particular advantage in sudden death, since death will come soon enough from normal geriatric pathology. The trait of sudden death will not have had the necessary time to evolve.
setting: rural Hurley Township, Ulster County, New York
Today Gretchen and I drove down to Silver Spring to visit her folks, who were just returning from a two month work-related stay in Dehli, India. The main business of our trip was to return the two geriatric Standard Poodles we've been dog sitting for the past two months. Fearing a possible winter storm, we set off the moment Gretchen got home from teaching her class at the community college. We put down the two back seats of our tiny Honda Civic hatchback, tossed in three large dog beds, and loaded up the two poodles, our two dogs, and a few light pieces of luggage. We also brought along a cat carrier and our elderly cat Marie (aka "the Baby") so she wouldn't have to endure the cold house in our absence. (The four other cats are younger and tough enough to handle it.) Marie likes to sit in our laps and purr contentedly while we drive, although south of New Paltz she suffered a bout of motion sickness and yacked up her lunch.
The weather was fine all the way to the bottom of New Jersey, but we hit some bad traffic on the Garden State Parkway north of where it crosses I-80, and so managed to lose a half hour in gridlock. We also hit torrential bands of rain in Delaware and east of Baltimore, but still the trip didn't take much more than six hours. Aside from the doggy biomass blocking the rearview and the gridlock, the main thing excruciating about this drive was our attempt to listen to Assassination Vacation, a book by Sarah Vowell, recorded on CDs. It was Sarah Vowell herself who was doing the reading. For those who have never heard Sarah Vowell's voice, I'll briefly describe it as resembling that of an eight year old girl who has, say, a penchant for popping quaaludes. I'd grown comfortable with this voice on This American Life, but hearing her reading an entire book was more than either of us could stand. We made it about half way through.
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