Digital Genetics, Variation, Evolvability, and the Evolution of Programmed Aging.

A major unresolved issue in gerontology concerns the evolutionary nature of senescence: Is aging caused by genetically programmed evolved mechanisms because limiting individual lifespan increases a population's ability to survive and grow? Or is aging non-programmed because aging reduces an individual's ability to survive and reproduce? There has been little disagreement with the many proposed population benefits of senescence, but evolution theory as described by Darwin and currently taught is very individual-oriented and until recently, programmed aging has been widely thought to be theoretically impossible. However, genetics discoveries have exposed issues with traditional theory that support population-driven evolution and programmed aging. In particular, as described in this article, the discovery that biological inheritance involves the transmission of information in digital form between parent and descendant of any organism strongly supports population-oriented evolution concepts and dependent programmed aging theories. A related issue concerns evolvability. Traditional theory assumes that the ability to evolve (evolvability) and involving mutations and natural selection is an inherent property of life. Evolvability theories suggest that evolvability in complex species is instead mainly itself the result of evolved traits and that such traits can evolve even if individually adverse. Programmed aging theories based on evolvability suggest that aging has evolved because it increases evolvability causing a population benefit. This idea is also strongly supported by the digital nature of inheritance. The programmed vs. non-programmed issue is critical to medical research because the two concepts suggest that very different biological mechanisms are responsible for aging and most instances of age-related disease.

Evolvability, Population Benefit, and the Evolution of Programmed Aging in Mammals.

Programmed aging theories contend that evolved biological mechanisms purposely limit internally determined lifespans in mammals and are ultimately responsible for most instances of highly age-related diseases and conditions. Until recently, the existence of programmed aging mechanisms was considered theoretically impossible because it directly conflicted with Darwin's survival-of-the-fittest evolutionary mechanics concept as widely taught and generally understood. However, subsequent discoveries, especially in genetics, have exposed issues with some details of Darwin's theory that affect the mechanics of the evolution process and strongly suggest that programmed aging mechanisms in humans and other mammals can and did evolve, and more generally, that a trait that benefits a population can evolve even if, like senescence, it is adverse to individual members of the population. Evolvability theories contend that organisms can possess evolved design characteristics (traits) that affect their ability to evolve, and further, that a trait that increases a population's ability to evolve (increases evolvability) can be acquired and retained even if it is adverse in traditional individual fitness terms. Programmed aging theories based on evolvability contend that internally limiting lifespan in a species-specific manner creates an evolvability advantage that results in the evolution and retention of senescence. This issue is critical to medical research because the different theories lead to dramatically different concepts regarding the nature of biological mechanisms behind highly age-related diseases and conditions.

Externally Regulated Programmed Aging and Effects of Population Stress on Mammal Lifespan.

Programmed (adaptive) aging refers to the idea that mammals, including humans and other complex organisms, have evolved mechanisms that purposely cause or allow senescence or otherwise internally limit their lifespans in order to obtain an evolutionary advantage. Until recently, programmed aging had been thought to be theoretically impossible because of the mechanics of the evolution process. However, there is now substantial theoretical and empirical support for the existence of programmed aging in mammals. Therefore, a comprehensive approach to medical research on aging and age-related diseases must consider programmed aging mechanisms and the detailed nature of such mechanisms is of major importance. Theories of externally regulated programmed aging suggest that in mammals and other complex organisms, genetically specified senescence mechanisms detect local or temporary external conditions that affect the optimal lifespan for a species population and can adjust the lifespans of individual members in response. This article describes why lifespan regulation in response to external conditions adds to the evolutionary advantage produced by programmed aging and why a specific externally regulated programmed aging mechanism provides the best match to empirical evidence on mammal senescence.

Arguments against non-programmed aging theories.

Until recently, non-programmed theories of biological aging were popular because of the widespread perception that the evolution process could not support the development and retention of programmed aging in mammals. However, newer evolutionary mechanics theories including group selection, kin selection, and evolvability theory support mammal programmed aging, and multiple programmed aging theories have been published based on the new mechanics. Some proponents of non-programmed aging still contend that their non-programmed theories are superior despite the new mechanics concepts. However, as summarized here, programmed theories provide a vastly better fit to empirical evidence and do not suffer from multiple implausible assumptions that are required by non-programmed theories. This issue is important because programmed theories suggest very different mechanisms for the aging process and therefore different mechanisms behind highly age-related diseases and conditions such as cancer, heart disease, and stroke.

On the programmed/non-programmed aging controversy.

The programmed vs. non-programmed aging controversy has now existed in some form for at least 150 years. For much of the XX century, it was almost universally believed that evolution theory prohibited programmed (adaptive) aging in mammals and there was little direct experimental or observational evidence favoring it. More recently, multiple new evolutionary mechanics concepts that support programmed aging and steadily increasing direct evidence favoring it overwhelmingly support the existence of programmed aging in humans and other organisms. This issue is important because the different theories suggest very different mechanisms for the aging process that in turn suggest very different paths toward treating and preventing age-related diseases.