Why we die

I was reading an interesting article in American Scientist about the statistics of death, courtesy of the Seed Daily Zeitgeist. The author was making sense of the statistics of predicting death rates across age groups and determining the life expectancy of a population. The conclusion of the article attempts to then make sense of why we die. He offers a few explanations: evolution favoring young, virile baby-makers, a catastrophic buildup of mutations resulting in cancers, our own telomere time bomb. But I think he fails to consider one of the most important reasons for death; evolution must clear out previous generations to make room for the new hotness.

Evolution depends on mutation. I like to think about it in the following thought experiment. Say there are two species living in close proximity. One species can live indefinitely, the other species has a limited generation time. The second species has a strong incentive to reproduce and a better potential to generate useful mutations. The first species eternally languishes as the same generation watches their competitors cycle through generations. Eventually a positive mutation will arise in the second species and it will be able to overtake the other, stagnant species.

Evolution requires that generations turn over. The speed we do is probably best described by Stephen Jay Gould in Ontogeny and Phylogeny. He talks about k and R selection, which define two ideal states that a species experiences. In one state, resources are abundant and there is strong pressure to produce many offspring as quickly as possible. These animals reproduce quickly and die just as fast. The other state is of a stable population with limited resources which eventually develops a slow, long generation time to maximize the resources available to the population.

We definitely die because our telomeres shorten, senescing our body cells. We die because mutations build up in our cells and cancerous cells outcompete our own cells, and we die as machines as our vital systems degrade and shut down. These are not independant variables, they are determined by evolution, which once balanced us against a pleistocene backdrop. They are related because they also balance each other. We should stop considering ourselves as victim observers of a harsh world, we are a dynamic part of the history and ecosystem of this planet.