The other day I (among others) came down on Gregg Easterbrook for his poor grasp of science. Finding myself procrastinating today, I wandered over to his blog and had yet another good laugh. In a post today, he actually displays some interest in evolutionary biology. After discussing some work suggesting that wine might be able to prolong life, he gets into the evolution of longevity. I raised my eyebrows at this point, thinking perhaps he'd moved away from the muddled stuff he's written about evolution in the past. But then the goofiness returns.
First he describes how experiments to extend the lifespan of flies and other lab animals with a low-calorie diet makes them sterile, and declares, " It's as if evolution declared: If you're going to have sex and make more of yourselves, then you must die and get out of the way."
Then later, he argues that "evolution seems to have wanted us to grow to sexual maturity, reproduce, care for young through infancy, and then be gone. After that, natural selection loses interest in us entirely, evolving little if anything in the way of life-extension. The low-calorie-diet cellular defense may be in our genes to increase an organism's odds of living until reproduction through the famines and poor hunts that must have characterized the primordial world."
If you can manage to hack your way through the vague language, you get to an insoluble contradiction--either longevity means you can have kids, or it means you can't. Which is it?
Easterbrook's super-simplistic picture of evolution fails in other ways as well, such as the way he writes about how evolution "wants" anything at all. (Does an apple fall because gravity wants it?) And while he's right to say that senescence is shaped by evolution, he offers a one-size-fits-all explanation. He has no way of explaining why humans live for decades, and many species only a few days or weeks. Why do women experience menopause long before they die? Evolutionary biologists see longevity as the product of several trade-offs. It depends in part on the risk of death from predators, the cost of producing offspring, and the advantages or disadvantages of older members in a group. There's some evidence, for example, that menopause is part of a life-history strategy to allow human grandmothers to invest in the success of their grandchildren, rather than have more children of their own.
But in the end, Easterbrook's not really interested in these mundane details. He concludes his biology lesson this way:
"The fact that our bodies seemed designed to live much less longer than possible seems evidence that the human form is the result of an unguided natural process. Perhaps God struck the spark of life, then allowed evolution to determine the rest. If God made us specifically, why cause our lives to be needlessly short? I guess we can be allowed to dream that the reason is God is eager to show us something better than this world."
Take a moment, if you need to, to reread this. Yes, he really did write that. I guess I can be allowed to dream that God is waiting most eagerly for the mayfly, which He made to live only a day.
Mayflies do NOT live for a day, even as "adults". Of the over 2000 species worldwide, we find those that live for 1, 2, 3 years or more. What you refer to is the short lives of the (two) winged (pre-)reproductive stages, called (sub-)imagos, which last for up to several days. The larval or nymphal stages last for most of the minimum one year lifespan of these insects.
As you can tell by all the weasel words, there is alot of variation involved, but no mayfly species lives for a day.