Thesis 27

Thesis #27 – Among populations which have had their forces of natural selection strengthened experimentally, detectable improvements in adult survival and reproduction have been observably achieved within dozens of generations.


So there I am, in 1977, realizing that all evolution has to do to postpone aging is have its force of natural selection strengthened during adulthood by shifting the age of first reproduction.  What was not clear then was whether or not it could do so quickly.

The experimental material I used to test this idea was a laboratory population of the fruit fly, Drosophila melanogaster, which I was maintaining at moderate populations sizes of around 1,000 to 2,000 individuals.  Would this population have the genetic variation I needed to test the idea of slowing aging by shifting the age at which natural selection would start to fail?

At that time, I was engaged in laboriously testing that population for its quantitative genetic variation.  But I wouldn’t get all the results I needed for another 16-18 months.  So, impetuously, I just gambled that it would be there.  Fortunately, my advisor was away for the year, and couldn’t talk me out of this plan.  Nor did I have to appeal to a “better not” grant-review panel.

I took that fruit fly population and split it into controls, which were reproduced at 14 days of age from when they were eggs, and an experimental population, which reproduced at 35 days of age.  I then maintained these two populations like this for a dozen generations of late-reproducing flies, about a year.  Then I reared them in parallel, and observed their pattern of reproduction and survival as adults.

The results were that the population with postponed first reproduction, an increased b in Hamilton’s terminology, had a significantly increased average lifespan and a shift of reproduction from early to later ages.  That is, my bet had worked.  In only a year, my delayed-reproduction fruit flies had their pattern of aging evolutionarily shifted toward slowed aging.

Since then, this experiment has been repeated many times by myself and others, with fruit flies, other insects, and even mice, and the results have been qualitatively consistent.  Shifting the first age of reproduction upward quickly results in the evolution of increased lifespan and somewhat slower aging.  Even with the bad technique that prevails in most biological laboratories, this experiment is easily done, and the results are predictable.

This was the experimental breakthrough that has served as a crack in the edifice of conventional theories of aging, a crack through which the waters of scientific change have seeped ever since.  The journals and the grant-reviewing panels have mightily resisted this scientific change, as we can expect that they always will resist substantive reform of conventional views.  But the power of strong-inference science cannot be resisted forever, not even by biologists and physicians, as those of us who are the scientific descendants of Charles Darwin know well.  We evolutionary biologists all grow up intellectually on tales of the obdurate stupidity of scientific establishments.

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