Quality–quantity trade-off of human offspring under adverse environmental conditions J. J. MEIJ, * D. VAN BODEGOM,* J. B. ZIEM,  J. AMANKWA, à A. M. POLDERMAN,§ T. B. L. KIRKWOOD, – A. J. M. DE CRAEN,* B. J. ZWAAN** & R. G. J. WESTENDORP* *Department of Gerontology and Geriatrics, Leiden University Medical Center, Leiden, The Netherlands  School of Medicine and Health Sciences, University of Development Studies, Tamale, Ghana àGhana Health Service, Ministeries, Accra, Ghana §Department of Parasitology, Leiden University Medical Center, Leiden, The Netherlands –Institute for Ageing and Health, Newcastle University, Newcastle upon Tyne, UK **Institute of Biology, Leiden University, Leiden, The Netherlands Introduction Life-history theory predicts that during evolution resource acquisition is maximized and that adaptation to the prevailing environmental conditions is realized by differential resource allocation. For any plant or animal species, reproduction is a costly process, and many resources are allocated to reproduction, at the expenses of other processes such as growth and maintenance. For reproduction a further division of resources can be predicted; reproductive investment in quality and quan- tity of offspring. For different species or different popu- lations of the same species, the precise balance between quality and quantity of offspring will depend on the selective forces operating, such as the shape of the reproductive effort curve, the presence of parent off- spring conflicts and the availability of resources in the environment (Roff, 1992; Stearns, 1992). The trade-off between quality and quantity of offspring is well known in plants, for example in seed number and size (Salisbury, 1942; Harper et al., 1970). Moreover, both between and within animal species, a strong negative association between number and survival of offspring is found (Lack, 1947; Macarthur & Wilson, 1967; Smith & Fretwell, 1974). Most evidence of animal studies comes from birds. Here, increasing clutch size was found to be related to lower offspring survival (Perrins & Moss, 1975), a finding also reproduced in experimental studies in diverse species (Gustafsson & Sutherland, 1988; Dijkstra et al., 1990; Hardy et al., 1992; Koskela, 1998; Charnov & Ernest, 2006) including nonhuman primates (Walker et al., 2008). As early as Becker (1960) there has been an interest in the trade-off in humans. To Correspondence: D. van Bodegom, MD, Department of Gerontology and Geriatrics, LUMC, PO Box 9600, 2300 RC Leiden, The Netherlands. Tel.: +31 71 5266640; fax: +31 71 5248159; e-mail: d.van_bodegom@lumc.nl The first two authors contributed equally to the study. ª 2009 THE AUTHORS. J. EVOL. BIOL. 22 (2009) 1014–1023 1014 JOURNAL COMPILATION ª 2009 EUROPEAN SOCIETY FOR EVOLUTIONARY BIOLOGY Keywords: Africa; fertility; life-history theory; offspring survival; quality-quantity trade-off; reproductive succes. Abstract A central paradigm in life-history theory is the trade-off between offspring number and quality. Several studies have investigated this trade-off in humans, but data are inconclusive, perhaps because prosperous socio-cultural factors mask the trade-off. Therefore, we studied 2461 offspring groups in an area under adverse conditions in northern Ghana with high fertility and mortality rates. In a linear mixed model controlling for differences in age and tribe of the mother and socioeconomic status, each additional child in the offspring group resulted in a 2.3% (95% CI 1.9–2.6%, P < 0.001) lower proportional survival of the offspring. Furthermore, we made use of the polygamous population structure and compared offspring of co-wives in 388 households, thus controlling for variation in resources between compounds. Here, offspring survival decreased 2.8% (95% CI 2.3–4.0%, P < 0.001) for each increase in offspring number. We interpret these data as an apparent quality–quantity trade-off in human offspring. doi: 10.1111/j.1420-9101.2009.01713.x