The Evolution of Evolvability and Programmed Aging

The evolution concept has two distinct parts. The facts of evolution can be summarized as follows: Humans, and other current species are descended from earlier different species, that in turn were descended from still earlier species, that were ultimately descended from a very simple (single-cell) organism that lived billions of years ago (the universal common ancestor). Our scientific certainty in this part of Darwin’s 1859 idea has steadily increased for more than 160 years and there is currently essentially no scientific disagreement.

The second part concerns the mechanics of evolution or how the evolution process works. Here we have the reverse situation. Darwin’s concept involving mutations and natural selection is very individual-oriented: The evolution process causes organisms to acquire design characteristics that increase a wild individual’s ability to produce descendants. This idea plausibly fits the vast majority of observations concerning organism evolved design characteristics (traits) and Darwin’s ideas were virtually unopposed (scientifically) until the 1950s.

There was a problem: It was immediately obvious that aging in mammals did not fit with Darwin’s concept. Aging did not help an individual produce more descendants despite otherwise strongly appearing to be an evolved trait. Aging, because of the gross reduction in fitness aspects such as strength and sensory acuity clearly reduced the probability that an individual would produce descendants. In many other organisms, internally caused death could be explained by some evolved feature that increased reproduction at the expense of additional lifetime and indeed some species only reproduce once. This idea did not apply to mammals

Despite more than a century of effort no theory has been produced that plausibly explains observed mammal aging while simultaneously maintaining full compliance with Darwin’s individual-oriented mechanics concept.

The idea that we possess an evolved biological mechanism that purposely limits lifespan (essentially a suicide mechanism) certainly directly conflicts with evolutionary mechanics as generally understood despite increasing evidence and theoretical support. In 2022 there is still no wide scientific agreement on a solution to this problem and therefore no agreement on even the general nature of aging. Biology courses still typically state that evolution works entirely on an individual level and fail to mention the substantial disagreements. However, discoveries, especially in genetics, have exposed issues with the Darwinian mechanics concept specifically regarding the individual vs population issue. Multiple concepts now propose that evolution is more population-oriented. As shown in the figure, our collective confidence that we understand the mechanics of evolution has actually declined and the number of different mechanics concepts has increased! All of the more recent concepts are at least somewhat population-oriented. That is, they suggest that evolution is at least partly driven by the success (non-extinction and growth) or failure (extinction) of populations.

Timeline of Evolutionary Mechanics Theories

The most recent and least-known modern mechanics concept is evolvability, which can be defined as a species population’s ability to evolve or more exactly as the rapidity and precision with which a population can genetically adapt to changes in its external world. A population that could adapt more rapidly or comprehensively to changes in their world would have an evolutionary advantage over a similar population with less evolvability. Where Darwin’s concept suggests that the ability to evolve is an inherent property of all living organisms, the evolvability concept suggests that the ability to evolve is itself mainly the result of evolved characteristics that increase evolvability.

Theorists have now suggested multiple ways in which internally limiting lifespan enhances the probability that a population will survive and grow by increasing evolvability. The reason that this is critically important to anti-aging medicine is that these theories support the idea that there exists a treatable common cause of the many different manifestations of aging and therefore the idea that aging can be generally delayed. Further, evolvability theories of aging suggest different biological mechanisms cause aging and therefore suggest different possibilities for treatment approaches relative to aging theories based on other population-oriented concepts.

The need for evolvability can vary greatly between populations. Some clams and trees have apparently existed for millions of years with little change or need for adaptation. Mammals typically occupy a food-chain in which different species force adaptation on other species. A predator could evolve better ways for catching prey. The prey can evolve better ways to evade predators. This observation might explain why some clams and trees have extremely long lifespans while mammals have lifespans that are tightly controlled.

Future posts will describe why aging increases evolvability.

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