Population and Development Review, Volume 27, Number 3
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POPULATION AND DEVELOPMENT REVIEW James R. Carey and Debra S. VOLUME 27 NUMBER 3 Judge Life span extension in humans is S E P T E M B E R 2 0 0 1 self-reinforcing: A general theory of longevity Alexander A. Weinreb First politics, then culture: Accounting for ethnic differences in demographic behavior in Kenya Ulrich Mueller Is there a stabilizing selection around average fertility in modern human populations? Zai Liang The age of migration in China Notes and Commentary G. P. Freeman and R. Birrell on divergent paths of immigration politics in the United States and Australia Data and Perspectives R. Schoen and N. Standish on the retrenchment of marriage in the US Archives William Farr on the economic value of the population Book Reviews Review essays by J. E. Cohen and J. A. Goldstone; reviews by J. Mokyr, D. Hodgson, P. Heuveline, E. D. Carlson, J. T. Boerma, and others Documents The socioeconomic impact of the HIV/AIDS epidemic Population and Development Review seeks to advance knowledge of the interrelationships between population and socioeconomic development and provides a forum for discussion of related issues of public policy. EDITOR Paul Demeny MANAGING EDITOR Ethel P. Churchill EDITORIAL COMMITTEE Paul Demeny, Chair Geoffrey McNicoll Ethel P. Churchill Michael P. Todaro Susan Greenhalgh EDITORIAL STAFF Robert Heidel, Production Editor Y. Christina Tse, Production/Design Margaret A. Knoll, Circulation Sura Rosenthal / Mike Vosika, Production ADVISORY BOARD Gustavo Cabrera Milos˘ Macura John C. Caldwell Carmen A. Miró Mercedes B. Concepción Asok Mitra Richard A. Easterlin Samuel H. Preston Akin L. Mabogunje Signed articles are the responsibility of the authors. Views expressed in the Review do not necessarily reflect the views of the Population Council. 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POPULATION AND DEVELOPMENT REVIEW VOLUME 27 NUMBER 3 S E P T E M B E R 2 0 0 1 ARTICLES Life Span Extension in Humans Is Self-Reinforcing: A General Theory of Longevity 411 JAMES R. CAREY DEBRA S. JUDGE First Politics, Then Culture: Accounting for Ethnic Differences in Demographic Behavior in Kenya 437 ALEXANDER A. WEINREB Is There a Stabilizing Selection Around Average Fertility in Modern Human Populations? 469 ULRICH MUELLER The Age of Migration in China 499 ZAI LIANG NOTES AND COMMENTARY Divergent Paths of Immigration Politics in the United States and Australia 525 GARY P. FREEMAN BOB BIRRELL DATA AND PERSPECTIVES The Retrenchment of Marriage: Results from Marital Status Life Tables for the United States, 1995 553 ROBERT SCHOEN NICOLA STANDISH ARCHIVES William Farr on the Economic Value of the Population 565 BOOK REVIEWS Linking Human and Natural History: A Review Essay JOEL E. COHEN 573 Population and Progress in the Middle Ages: A Review Essay JACK A. GOLDSTONE 585 Julian L. Simon, The Great Breakthrough and Its Cause, edited by Timur Kuran JOEL MOKYR 596 Angela Hattery, Women, Work, and Family: Balancing and Weaving DENNIS HODGSON 599 John I. Clarke, The Human Dichotomy: The Changing Numbers of Males and Females PATRICK HEUVELINE 600 Giovanni Andrea Cornia and Renato Paniccià (eds.), The Mortality Crisis in Transitional Economies ELWOOD D. CARLSON 602 Caleb E. Finch, James W. Vaupel, and Kevin Kinsella (eds.), Cells and Surveys: Should Biological Measures Be Included in Social Science Research? J. TIES BOERMA 605 Short Reviews 608 DOCUMENTS On the Socioeconomic Impact of the HIV/AIDS Epidemic 619 ABSTRACTS 625 AUTHORS FOR THIS ISSUE 632 Life Span Extension in Humans Is Self-Reinforcing: A General Theory of Longevity JAMES R. CAREY DEBRA S. JUDGE MORE THAN TWO decades ago gerontologist George Sacher (1978) noted that the approach to one basic question in the biology of aging, “Why do we grow old?,” is guided largely by a research paradigm involving model sys- tems designed to compare biological functions—those of individual organ- isms—in old and young animals. One of his primary concerns with this ag- ing-oriented approach to understanding longevity was that the far-reaching physiological, cellular, and molecular correspondence between model sys- tems (mice) and humans concealed a paradox: if model species are so simi- lar to humans in molecular makeup that they can serve as models, why do mice age as much in 2 years as humans do in 70 years? This paradox moti- vated him to ask his second question: “Why do we live as long as we do?” This question cannot be answered within the framework of developmental research on aging, but rather requires the formulation of an evolutionary- comparative paradigm concerned with longevity. We use longevity as a gen- eral term for three separate but interrelated measures having to do with length of life: maximum observed life span defined as the highest verified age at death, maximum potential life span defined as the theoretical high- est attainable age, and mean life span defined as the expected average num- ber of years of life, or life expectancy.1 Despite the arguments by Sacher and others (e.g., Hayflick 2000) in support of developing a longevity-oriented theory of the finitude of life, no such theory has ever been published. Our objective in this article is to de- scribe a general theory of longevity extension in social species, particularly as it applies to humans. The central concepts of such a theory derive from patterns identified in life span data for vertebrates (Carey and Judge 2000), insects (Carey 2001b), and humans (Kannisto et al. 1994; Tuljapurkar, Li, and Boe 2000; Vaupel et al. 1998; Wilmoth et al. 2000); from environmen- tal factors associated with the evolution of extended longevity in insects POPULATION AND DEVELOPMENT REVIEW 27(3):411–436 (SEPTEMBER 2001) 411 Click here to print article Click to return to Table of Contents 412 L IFE SPAN EXTENSION IN HUMANS (Carey 2001a, 2001b); and from the preliminary idea that longevity exten- sion in humans is self-reinforcing2 as first proposed by us (Carey and Judge 2001). Our theory also builds on and extends work by Fogel (1993, 1994, 1997) on what he and his colleagues refer to as “technophysio evolution”—a theory explaining the decline in morbidity and mortality since 1700. A theory of longevity that extends beyond the classical evolutionary theory of aging is important for several reasons. First, whereas senescence is a byproduct of evolution (Medawar 1955), life span is an evolved life-history trait that re- sults from positive natural selection. Second, unlike the evolutionary theory of senescence, which is based solely on individual natural selection (Williams 1957), this theory includes processes of sexual selection and kin selection, bringing life-history theory more fully to bear on questions concerned with the latter portion of the life cycle. Third, longevity-oriented theory allows consideration of behaviors that are characteristic of older individuals, including divisions of labor and intergenerational transfers (Beshers and Fewell 2001).