Abstract
In 1966, William D. Hamilton published a landmark paper in evolutionary biology: "The Moulding of Senescence by Natural Selection." It is now apparent that this article is as important as his better-known 1964 articles on kin selection. Not only did the 1966 article explain aging, it also supplied the basic scaling forces for natural selection over the entire life history. Like the Lorentz transformations of relativistic physics, Hamilton's Forces of Natural Selection provide an overarching framework for understanding the power of natural selection at early ages, the existence of aging, the timing of aging, the cessation of aging, and the timing of the cessation of aging. His twin Forces show that natural selection shapes survival and fecundity in different ways, so their evolution can be somewhat distinct. Hamilton's Forces also define the context in which genetic variation is shaped. The Forces of Natural Selection are readily manipulable using experimental evolution, allowing the deceleration or acceleration of aging, and the shifting of the transition ages between development, aging, and late life. For these reasons, evolutionary research on the demographic features of life history should be referred to as "Hamiltonian."
Highlights
From these equations and some numerical calculations, Hamilton (1966) argued that Fisher’s (1930) reproductive value is not a valid explanation of the existence of aging, if aging is defined as an endogenous decline in adult life-history characters, which seems to have been Hamilton’s definition. (Here we use the term “life history” to refer to the complete spectrum of age-specific survival probabilities and fecundities, whether these characters are components of fitness or not.) Hamilton gave examples of life histories that produce steadily increasing reproductive value, when Hamilton’s s(x) function instead always declines
THE TERMINAL PLATEAUS OF HAMILTON’S FORCES OF NATURAL SELECTION In 1992, Carey et al and Curtsinger et al published experimental data from large dipteran populations demonstrating that agespecific rates of mortality stop increasing at late ages and so “plateau.” Several studies have corroborated these findings in a variety of organisms, including humans (Vaupel et al 1998)
Charlesworth’s original expectations have not been born out. (We offer an explanation of this below, after discussing other quantitative genetics research on life history.)
Summary
From these equations and some numerical calculations, Hamilton (1966) argued that Fisher’s (1930) reproductive value is not a valid explanation of the existence of aging, if aging is defined as an endogenous decline in adult life-history characters, which seems to have been Hamilton’s definition (see Rose 1991). (Here we use the term “life history” to refer to the complete spectrum of age-specific survival probabilities and fecundities, whether these characters are components of fitness or not.) Hamilton gave examples of life histories that produce steadily increasing reproductive value, when Hamilton’s s(x) function instead always declines. The Taiwanese life-table that he used exhibited higher rates of early reproduction
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