Core thesis
DESTA proposes that senescence is an adaptive, programmatic continuation of the growth-termination process. Unavoidable diseconomies of scale favor growth termination; sexual selection maintains the growth-termination phenotype across generations; and the same regulatory systems that terminate growth continue operating throughout adulthood, producing the physiological changes recognized as senescence.
In this framework, aging is not fundamentally a cellular process. Cellular and molecular manifestations of aging are downstream consequences, markers, and mediators of a centrally regulated organism-level process.
Growth termination changes adulthood
Prior to growth termination, surviving longer often allows an organism to become larger, more experienced, more competitive, more reproductively successful, and less vulnerable to many forms of mortality. Fitness can continue increasing because growth itself continues to generate advantages.
Increasing size also produces increasing costs. As organisms become larger and more complex, they require greater structural support, longer developmental periods, more elaborate physiological coordination, increased resource consumption, and more extensive maintenance. These costs are the diseconomies of scale that ultimately favor growth termination in many terrestrial animals.
Once growth has ceased, the organism remains exposed to predation, disease, accidents, environmental stress, competition, and other unavoidable extrinsic fitness threats. Yet it can no longer substantially improve fitness through continued increases in size. This transition changes the fitness economics of adulthood and increases the relative importance of offspring fitness.
Intrinsic growth terminators and extrinsic growth slowers
DESTA distinguishes intrinsic growth terminators from extrinsic growth slowers. Intrinsic growth terminators, especially many terrestrial animals, possess internally regulated growth termination. Extrinsic growth slowers, including many aquatic species, may continue growth through much of life because buoyancy and ecological conditions reduce some diseconomies of scale.
In continuously growing species, surviving longer can continue to produce direct fitness gains through increased size, fecundity, and predator resistance. In intrinsic growth terminators, those growth-related gains largely cease once adult size is reached, while extrinsic risks continue.
Sexual selection maintains senescence
DESTA proposes that sexual selection maintains senescence because senescence creates a visible age gradient among adults. This gradient allows mate choice systems to distinguish newly mature individuals from individuals that have persisted through a longer sequence of ecological challenges.
This does not mean that choosers simply prefer older individuals. The preferred point on the age gradient depends on ecological conditions. The critical requirement is that the age gradient exists, making accumulated survival history available to the mate-choice process.
Ecological function and lineage persistence
The senescent age gradient does more than inform mate choice. It also shapes mortality distribution. As senescence progresses, older adults become progressively more vulnerable to predation and other forms of mortality. This tends to direct mortality toward individuals that have already had substantial reproductive opportunity.
DESTA further proposes that this age structuring modifies predator-prey dynamics. Predators can obtain reproductive success by targeting more vulnerable older prey rather than continually escalating adaptations directed at newly mature, highly reproductive adults. In this way, senescence contributes to predator-prey stability and long-term lineage persistence.
Physiological implementation
DESTA argues that senescence is implemented through central homeostatic regulation rather than originating as a fundamentally cellular process. In vertebrates, this regulatory system is centered in the hypothalamus and associated neuroendocrine networks, including the suprachiasmatic nucleus (SCN).
The same systems that coordinate growth, maturation, reproduction, metabolism, immunity, autonomic function, and circadian organization continue operating after growth termination. Over adulthood, these systems progressively alter defended physiological setpoints and reduce the amplitude of endocrine, metabolic, autonomic, immune, reproductive, and circadian output.
Under this model, epigenetic clocks, telomere changes, stem-cell exhaustion, mitochondrial decline, immune aging, and other cellular markers are not the primary origin of aging. They are downstream manifestations of a centrally regulated senescent state.
Read the full paper
DESTA v15.20.3 is available here as a site download and through Zenodo.