arXiv subjects

Josh Mitteldorf

Publications and source records attributed to Josh Mitteldorf.

3 recordsLinked to original sources

arXiv2009

Female Fertility and Longevity

Does bearing children shorten a woman's life expectancy? Several demographic studies, historic and current, have found no such effect. But the Caerphilly cohort study is far the most prominent and frequently-cited, and it answers in the affirmative. Why has this study found an effect that others fail to see? Their analysis is based on Poisson regression, a statistical technique that is accurate only if the underlying data are Poisson distributed. But the distribution of the number of children born to women in the Caerphilly database departs strongly from Poisson at the high end. This makes the result overly sensitive to a handful of women with 15 children or more who lived before 1700. When these 5 women are removed from a database of more than 2,900, the Poisson regression no longer shows a significant result. Bi-linear regression relating life span to fertility and date of birth results in a positive coefficient for fertility.

q-bio.PE↗

arXiv2006

Demographic Homeostasis and the Evolution of Senescence

Existing theories for the evolution of aging and death treat senescence as a side-effect of strong selection for fertility. These theories are well-developed mathematically, but fit poorly with emerging experimental data. The data suggest that aging is an adaptation, selected for its own sake. But aging contributes only negatively to fitness of the individual. What kind of selection model would permit aging to emerge as a population-level adaptation? I explore the thesis that population dynamics is inherently chaotic, and that aging is selected for its role in smoothing demographic fluctuations. The logistic equation provides a natural vehicle for this model because it has played a central role in two sciences: Population growth in a resource-limited niche has long been modeled by the differential LE; and, as a difference equation, the LE is a canonical example of the emergence of chaos. Suppose that feedback about depleted resources generally arrives too late to avoid a wave of unsupportable population growth; then logistic population dynamics is subject to chaotic fluctuations. It is my thesis that aging is an evolutionary adaptation selected for its stabilizing effect on chaotic population dynamics.

q-bio.PE↗

arXiv2005

Another Way to Calculate Fitness from Life History Variables: Solution of the Age-Structured Logistic Equation

r-selection refers to evolutionary competition in the rate of a population's exponential increase. This is contrasted with K-selection, in which populations in steady-state compete in efficiency of resource conversion. Evolution in nature is thought to combine these two in various proportions. But in modeling the evolution of life histories, theorists have used r-selection exclusively; up until now, there has not been a practical algorithm for computing the target function of K-selection. The Malthusian parameter, as computed from the Euler-Lotka equation, is a quantitative rendering of the r in r-selection, computed from the fundamental life history variables mortality and fertility. Herein, a quantitative formulation of K is derived in similar terms. The basis for our model is the logistic equation which, we argue, applies more generally than is commonly appreciated. Support is offered for the utility of this paradigm, and one example computation is exhibited, in which K-selection appears to support pleiotropic explanations for senescence only one fourth as well as r-selection.

q-bio.PE↗