Thesis #37 – Patterns of aging, including the rates of decline of functional characters and the timing of any cessation in such decline, depend on the environments in which cohorts are raised and live as adults.
(Picture of Einstein talking to Leo Szilard – the man who had the insight to take Einsteins’s ideas about energy and conceive of a design for a bomb)
One of the commonplace results of aging research is the increase in lifespan that occurs when animals are given qualitatively good nutrition, but deprived of as many calories as they would consume ad libitum. As we have already discussed, this is a natural outcome of the cost of reproduction, because diminished diets, either quantitatively or qualitatively, typically shut down reproduction. With the curtailment of most or all reproduction, survival then benefits, providing there is no acute starvation.
But there are more general principles to be appreciated than this one. As we have already discussed, what natural selection accomplishes is a reflection of the previous environments an evolving population has been subjected to. Differences among these environments may involve more than quantitative levels of calories and other nutrients. Some environments are qualitatively different.
Such qualitative differences can then lead to major differences in life history, with significant changes in development, aging, and late life, after aging ceases. In particular, a sufficiently novel or toxic environment may lead to a lack of the age-independent adaptation required to allow a post-aging phase in which reproduction and survival are sustained.
Recent experimental work in my laboratory led by my present graduate student Marta Santos has supplied the following Drosophila results: (i) some evolutionarily novel environments lead to long-sustained aging phases, with late life either shifted to much later ages or entirely obliterated; (ii) adaptation to one environment can change aging in another environment with respect to both the rate of that aging and the timing at which it eventually ceases.
These experimental findings suggest that there is nothing absolute or environment-independent about patterns of aging, including its rate and the timing of its cessation. This raises the possibility that there may be environments in which human patterns of aging might be systematically different. As I will argue below, there may be ways of life which, if adopted by men and women, might entail significant slowing of their aging, as well as fostering its cessation.