~ThisWeek’s Citation CIassIc~ ~ Charlesworth B. in age-structured populations. Cambridge, England: Cambridge University Press, 1980. 300 p.

L [SChOOL of Biological Sciences. , England] - -- Populations of many species are age-structured, and tured populations. The unit process of evolution is the study of their ecology and evolution presents change in frequencies of alternative1 forms of the many theoretical difficulties. This book reviews most same gene within a local population, arid much of aspects ofthe ecological dynamics, thetheory of nat- the book is devoted to descnbing the mathematical ural and artificial selection, and the genetic effects of theory of such change. Research on this topic re- finite population size, as they apply to age-structured quired the prior developmentof demographic mod- populations. It applies the results to the general elsthat allowed the description of theage consposi- biological problem of the evolution of life-history phe- tion and dynamics of age-structured populations nomena such as senescence and age-specific patterns without reference to . This research was of reproduction. [The SSC/~and 5C1 indicate that pioneered by Leonhard Euler in the eighteenthcen- this book has been cited in over 285 publications.] tury, but its great development came ‘in the early twentieth century, particularly ‘in the hands of Lodoi and Leslie. was first introduced into demographic models (or vice versa) by J.B.S. Haldan& and H.T4. Norto& in the 1920s. After that time, the subject largely Iangiãhed until Age and Evolution the 1970s, when a nwtther ofworkers, including my- self, startedto reexamine the questions originally ex- Brian Charlesworth plored by Haldane and Norton. In part, this work Department of Ecology and Evolution was motivated by dissatisfaction with the elegantand simple solutionto the problem dealing Chicago, IL 60637-1503 with selection with age-structure, known as the Mal- thusian parametermethod,4 and introduced by LA. Fisher in his 1930 book. The firm quantitative basis for thirising about se- November 4, 1988 lection in age-structured populations provided by this work, reviewed in the first four chapters of my book, provides the startingpoint for theorizing about The subject of my book is the application of con- the ways in which can shape life cepts of demography to population genetics and evo- history. This is the subject of the final chapter. One lutionary theory, allowing the development of mod- result of wide generalsignificance is thefactthat the els of evolutionary processes in populations where intensity of natural selection is a function ofthe age individuals are differentiated by age and in which at which genes affecting the trait are expressed. matings can occurbetween individuals of widely dif- Otherthings being equal,genes with early acting of. ferent ages. Why should anyone careabout this eso- feds are more strongly selected than genes with teric topic enough to cite, if not read, the book? The equivalent but late effects. The sipuificanceof this reason is thatmany kinds of livingcreatures, includ- in relation to the evolution5 of aging was first per- ing man, have populations that are structuredwith ceived by P.R. Medawar, whose formulation was respect toage. Evolutionarybiologists have beenin- qualitatively sound but quantitatively wroop. It is trigued bythe quodion of how natural selection and now clear that the phenomenon of decline in per- other evolutionary forces mold the way in which fer- fonnance of most components of multicellular or- tility and survivorshipchange with age in such spe- ganisms with age is the evolutionary by-product of cies. Why, for example, should senescence (the de- this decline withage in theefficacy of naturalselec- cline with advancin~age in survival and fecundity) tion. be an apparently universal property ofmulticellular Thetheoretical literature on the evolution of life- organisms, apart from those that reproduceexclu- history characteristics has grown considerably since sively vegetatively? Why should there be such a di- 1979, the time at which my review of the literature versity of pafterns of reproductionand survival as was completed. In addition there is now a large functions of age among different species, ranging body ofempirical evidence, c,oth from comparisons from the centuryplantthat waits scoresof yearsbe- of different species and from genetic andecological fore flowering and then dies after a prodigious bout studies of variation within species, againstwhich the of reproduction to flies that develop overa few days theory has been tested.’ The general perspective and then reproducecontinuously overa few morel presented in my book (which was a summary of the Answers to such questions can only be obtained work of many biologists) seemsto have survivedthis it we have a property worked out theory of the way scrutiny well and helped (I hope) to stimulate this in which evolutionary processes work in age~struc- research.

I. Crow iF & Khnura St. An inuoduction ~opopulation ~rzredcs theory. New York. Harper & Row, 2970. 592 p. (Cited 1,065 trues.) 2. Haldane J 8 S. A mathematical theoty of natural and artificial sel~ion.Part IV. Ptec. Camb. Philos. Soc. 23:607-IS. 1927. (CiteS 20 times time 1943.) 3. NoiSes H T J. Natural selection and Meraleliat, variation. JSoc. Lorxk,n Math. Soc. 28:2-45, 2928. (Cited 25 times since 1945.) 4. Fttbar R A. The geneocai ~ry ofnatural rejection. Oxford, England: , 1930. 291 p. (Cited 1,565 tunes since 1943.) 5. Mediwir PB. An unsolved pn,bkrn of biology. London: Lcwis. 2952. p. 26. (Cited 90 times.) 6. P5rliidge L & Haney P H. The ecolOgical context of life history evolution. Science 241:1449-55. 1988.

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