Fight Aging!

Researchers who theorize that aging is the result of damage accumulation have to explain why evolutionary processes fail to select for longer lives by favoring, say, better mechanisms for damage repair. These explanations exist and are generally robust, though there is always some ongoing level of debate over details, such as why we humans live for so long in comparison to other primates or other mammals our own size. Researchers who theorize that aging is an evolved genetic program have the opposite challenge, which is to explain how evolution selects for shorter lives than would otherwise be the case: what is the value of death-assurance mechanisms? Here too explanations exist, are generally robust, and there is an ongoing level of debate over details.

The mainstream consensus of the research community supports the view of aging as damage rather than aging as a genetic program, both from the point of view of molecular biology and evolutionary considerations. It is worth noting that even in a world in which aging is damage accumulation, the world in which I believe we live in, there can still be species that appear to suffer programmed aging on top of that. Salmon are a good example: it's worth looking into what that looks like as a response to external environmental factors.

Here, as a matter of interest, is a paper on the core issue relating to the hypothetical evolution of programmed aging: how can internal death-promoting mechanisms be adaptive for a species? This paper is open access, but note that it has no abstract - you'll have to click on the "Full Text" tab to view it, or alternatively download the PDF version.

Are Internal, Death-Promoting Mechanisms Ever Adaptive?

The idea that self-inflicted organismal death could be adaptive sounds, at face value, absurd. An adaptation is a trait that is suitable (apt) for the current circumstances or environmental challenges, and archetypal examples include traits that promote survival. Natural selection is the mechanism that produces adaptations. In describing natural selection, Darwin (1859) emphasized the struggle for survival: "Two canine animals in a time of dearth may be truly said to struggle with each other which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought......". How could an inherited trait that promotes death, rather than survival, possibly be adaptive?

Four categories encompass the major possible evolutionary explanations for the cause of death of an organism. First, death (or an increased probability of death) could inevitably occur despite the efforts or traits of the organism. Second, internal mechanisms that promote death could exist in spite of selective pressure against them. Third, death could occur as a side-effect of a mechanism within the organism that has another function or benefit. Fourth, death could occur because of a mechanism within the organism that evolved explicitly to cause death. This fourth category is the only one in which the mechanism promoting death is an adaptation for promoting death, and cases in this category can only be explained by selection at a hierarchical level other than the organism.

In all categories except the first, we can reasonably expect to see active mechanisms within an organism that promote death. This review was motivated by the observation that diverse organisms apparently have such active, internal death-promoting mechanisms and by the subtle and difficult conceptual issues that understanding the evolution of this kind of trait raises.