Thesis #26 – The forces of natural selection can be strengthened during adulthood by postponing the first age at which they begin to decline, which can be achieved for the force of natural selection acting on age-specific mortality by postponing the first age of reproduction.
Much of the first 25 theses focused on problems with prevailing views. That is, in large measure, to this point I have been setting about the destruction of conventional views concerning aging and the foundations of health, views that dominate Western medical thinking about medicine and cognate health issues.
But this would not be a very useful effort if it were little more than a critique of existing medical or gerontological thinking. Starting with this thesis 26, I will be setting out a positive alternative program, a set of ideas about experiments and health practices that can make a constructive difference to patterns of aging.
Let’s start with the first important idea I had as an experimentalist, in the fall of 1977. That was when I realized that the natural selection might quickly retune aging if it was artificially strengthened at later adult ages. A key parameter affecting the force of natural selection acting on survival is the first age at which a population begins to contribute offspring to the next generation. This parameter is conventionally labeled b.
Basically, the force of natural selection acting on survival is weighted according to the proportion of a population’s reproduction that lies in its future. By increasing the value of b in an experimental context, one would be strengthening the force of natural selection at all ages between the previous value of b and its new higher value. As a matter of biological practice, b can be shifted upward to a much higher value so long as there are enough fertile survivors available after the new first age of reproduction.
This was simple mathematics. But what remained unaddressed in 1977 was whether or not there would be enough standing genetic variation, or “heritability” in the language of quantitative genetics, for natural selection to respond quickly to this shift in the force of natural selection. At that time, we did not know how common such genetic variation was among outbred populations. In particular, many biologists, even evolutionary biologists, thought that genetic variation affecting characters like survival was pretty thin on the ground. That was because they were still thinking in terms of evolution in terms of intermittent, rare, beneficial genes arising by mutation and sweeping toward fixation.
A simple way to understand my career, and my reputation as a scientific rebel – if not rapscallion, is that my success as a scientist has been based on repeatedly betting against conventional wisdom. At times, when I have bet against the conventional wisdom, I was betting against the very beliefs that I had been inculcated in during my training. Thus, I was often betting against assumptions that I myself cherished, and might have been as unable to question as anybody else just weeks or months before.