How Evolutionary Thinking Affects our Ideas about Aging Interventions





Josh Mitteldorf

Dept of Mathematics, Temple University, Philadelphia, PA 19122



If we think that aging is caused by many parts of our bodies wearing out simultaneously, then we must address these problems one-by-one. If we think that the body is programmed to turn off its protective programs, or even to self-destruct, turning apoptosis and the immune system upon its own cells, then all we need to do is to thwart these programs, mimicking or interfering with the body's signal processes as we have done in so many other areas to good effect.

Evolutionary theory has taught that fitness consists in generating more offspring, sooner. What evolves is what is good for the individual. Aging is bad for the individual. Hence aging could not have evolved as an adaptation.

Nonetheless, there is substantial evidence that aging has evolved as an adaptation. Aging seems to be postponable, sometimes at no cost in fertility. There are mechanisms, programmed by genes, that seem to have no other purpose than to disable and ultimately to kill us.

We must consider the possibility that evolutionary theory has misled us. Nature's definition of fitness is far more "groupie" than the one that has dominated population genetic thinking for nearly 100 years. Diverse evidence for this hypothesis has been dismissed or brushed aside, case by case, because it so deeply contradicts established theory.

In this paper, I outline the full story of the distortion of priorities in medical research and the pessimism that evolutionary theory has imposed. I focus on the part of this story where my expertise lies, which is the evolutionary theory of cooperation: How can it be that natural selection is able to promote a trait that is as bad for the individual as aging, and benefits of which are far too diffuse to be explained by kin selection? Weismann's century-old hypothesis that aging promotes population diversity and a more rapid rate of adaptation in the population fails in quantitative models. But considerations of population dynamics supplies a context in which the evolutionary imperative to maximize reproductive potential is tempered. Every biological organism depends on an ecosystem, and every ecosystem has a characteristic time for restoring the resources that that organism consumes. It is not only counter-productive for the organism to evolve a higher rate of growth than the ecosystem can support; a population expansion rate that is significantly mismatched to the ecosystem's recovery rate actually risks chaotic population dynamics and prompt extinction.

When evolutionary theory is expanded to encompass ecosystem dynamics, the possibility emerges that the group imperative for demographic homeostasis may rival the selective pull toward higher reproductive value as an evolutionary force.




Key words: evolution, population dynamics, group selection







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