RESEARCH ARTICLE Primate Growth in the Slow Lane: A Study of Inter-Species Variation in the Growth Constant A Hannah Mumby Æ Lucio Vinicius Received: 1 May 2008 / Accepted: 6 October 2008 / Published online: 11 November 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Primates grow and develop slowly for mam- malian standards. Charnov showed that primates grow at only about 40% of the rates observed in other mammals of similar size. However, previous estimates of growth rates in primates were derived from regressions of adult body weight on age at first reproduction in different species, and therefore represent only an average trend for primates. Based on Charnov’s ‘growth law’, we estimated the growth constant A directly from published growth curves for 36 primate species from strepsirrhines to apes. We show that although primate growth is slow in all sampled species in comparison with the mammalian average, there is signifi- cant variation around the primate mean. Lemurids are particularly interesting due to their wide range of A values, and further study is required to determine whether envi- ronmental unpredictability could lead to the evolution of both very fast and very slow grow in different species. Results also indicate significant negative correlations between the growth constant A and both age at first reproduction and duration of the juvenile period, lending support to the juvenile risk hypothesis. Keywords Primates  Growth  Life history  Lemurids  Juvenile risk hypothesis Introduction Primates have been described as living ‘life in the slow lane’ (Stearns 1983; Harvey and Clutton-Brock 1985; Charnov and Berrigan 1993). In comparison with other mammals, primates exhibit slow growth rates, long juve- nile periods, low fertility and mortality rates, large neonates and longer lifespans than predicted for their body size (Ross 1998; Walker et al. 2006). Particular attention has been dedicated to the long and slow growth process in primates. Life history theory postulates that age at matu- ration (when investment of metabolic energy is switched from growth to reproduction) in a given species is deter- mined by a trade-off between growth and reproduction (Charnov 1993), i.e. as the compromise between the advantages of early sexual maturation and reproduction (that minimises the risk of death without reproduction; Johnson 2003, Kaplan et al. 2000) and the advantages of late growth termination (such as larger body size, higher social rank, decreased risk of predation among others; Stearns 1992). According to life history theory, primates would show late maturation relative to other mammals because of they are exposed to lower mortality rates and lower risk of death before reproduction, which favours prolonged investment in growth (Charnov and Berrigan 1993). Although life history theory satisfactorily accounts for the long duration of growth in primates, an explanation for their low growth rates remains elusive. Charnov (1993) proposed that body growth from weaning to adulthood in mammalian species can be modelled by the following ‘growth law’: dW dt ¼ A  W 0:75 Electronic supplementary material The online version of this article (doi:10.1007/s11692-008-9040-9) contains supplementary material, which is available to authorized users. H. Mumby  L. Vinicius (&) Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, The Henry Wellcome Building, Fitzwilliam Street, Cambridge CB2 1QH, UK e-mail: LVC22@cam.ac.uk 123 Evol Biol (2008) 35:287–295 DOI 10.1007/s11692-008-9040-9