Sex‐biased weaning and early childhood diet among middle holocene hunter–gatherers in Central California

Abstract

This article evaluates age of weaning and early childhood diets of eight males and nine females from a Middle Holocene (4300-3000 BP) site in Central California, CA-CCO-548. All individuals died as adults. d 15N values from serial sections of dentin collagen in first molars suggest females were fully weaned, on average, by 3.6 years of age, about 0.4 years later than males in the sample, suggesting possible greater parental investment in female offspring. However, throughout childhood females consumed lower trophic-level foods than males. This could indicate greater investment in males through provisioning of higher quality foods, or alternatively, some degree of independent foraging by males starting as early as 2 to 3 years of age. Even as adults, these same males and females consumed a different range of foods as indicated by their bone collagen d Humans are unique among primates in terms of child investment and weaning practices. Not only is there extreme variation between and within particular societies, but offspring are typically weaned at much earlier ages than non-human primates, such as great apes. For example, accounting for differences in growth rates and life history effects, humans breastfeed on average less than half as long as our close relatives, chimpanzees and gorillas (Dettwyler, 2004;Kennedy, 2005).Early human weaning and the nature of early childhood diets, as well as high interindividual variation in such practices, has been used to speculate on a number of evolutionary processes in our species' past (Trivers, 1974;Blurton-Jones, 1986;Sellen and Smay, 2001, Stearns, 1992;Kaplan, 1996;Borgerhoff-Mulder, 1992, 2001Piperata, 2009). These processes often pit the costs of longer breastfeeding to parents, especially mothers, against benefits to offspring. Breast milk is a significant energetic investment for a mother. It can negatively impact her health, require her to work harder to obtain calories, take away from time she could be working (opportunity costs), and decrease her ability to get pregnant again, lowering her fertility and overall fitness, as well as that of her male partner (Delgado et al., 1982;Borgerhoff-Mulder, 1992;Riordan, 2005;Sellen, 2006;Piperata and Mattern, 2011). On the other hand, breast milk provides a child with a reliable and easily digestible source of calories and nutrients. Empirical evidence suggests that extended breastfeeding offers long-term benefits to children, such as increased stature, better cognitive capabilities (e.g., higher IQ), greater immunity to some diseases, and lower rates of obesity (Taren and Chen, 1993; Mortensen et al., 2002;Schack-Nielsen and Michaelsen, 2006), effects also seen in non-human primates (Hinde et al., 2009). For these reasons, the age at which a mother weans a child has often been used as a proxy measure of parental investment in offspring (Stuart-Macadam and Dettwyler, 1995;Humphrey, 2010).Research in human behavioral ecology suggests that parents will reduce their investment in children in environments where increas...

Stable isotope evidence of juvenile foraging in prehistoric Central California

“…Consequently, stable isotope measures derived from bone collagen inform on the dietary protein sources consumed during the individual's last decades of life (Eerkens and Bartelink, 2013;Schwarcz and Schoeninger, 1991). Unlike bone, teeth do not experience tissue turnover and replacement, although secondary dentin growth may occur in the pulp cavity during adulthood (Hillson, 1986;White and Folkens, 2005).…”

“…At sites with a significant difference in dietary signatures between men and women, children's diets reflect adult sex differences (Eerkens and Bartelink, 2013). Unfortunately, the predicted isotopic signature of a child engaged in assistive foraging may not differ substantially from a child consuming a diet of adult-provisioned food, in which case the composition of their diet would also resemble the adult average at a site.…”

Reconstruction of breastfeeding and weaning practices using stable isotope and trace element analyses: A review

“…Furthermore, there are great individual variations in BWPs in modern traditional and industrialized human populations (Vitzthum, 1994). Individual variations in BWP cannot be discussed in most cross-sectional reconstructions, but can be in longitudinal reconstructions using isotopic signals in hair (Fuller et al, 2006a), serial sections of tooth dentin (Eerkens et al, 2011;Beaumont et al, 2013b;Eerkens and Bartelink, 2013;Henderson et al, 2014), and elemental signals in thin-sectioned tooth enamel (Humphrey et al, 2008a;Austin et al, 2013).…”

“…As a byproduct of BWP reconstructions from adult body tissues (see the previous section), sex differences can be easily investigated (Eerkens and Bartelink, 2013;Henderson et al, 2014). There is no conclusive sexing method of preadolescent subadult skeletons using morphological criteria, and sexing by ancient DNA analysis is not routinely performed (Lewis, 2007).…”

Stronger Together: Advancing a Global Bioarchaeology

“…This research is enhanced by analysis of stable isotopes from different parts of bones and teeth and among teeth that form at different times to reveal diet change over the life course and gain a better understanding of individual life histories, even in commingled deposits (e.g., Gregoricka 2014;. New techniques that examine serial (incremental) sections of tooth dentine (e.g., Beaumont et al 2013;Burt and Garvie-Lok 2013;Eerkens et al 2011), along with analyses of bone collagen and apatite, are advancing our understanding of the weaning process and the identification of a weaning diet, a post-weaning diet, and the age at which an adult diet is adopted (e.g., Dupras and Tocheri 2007;Eerkens and Bartelink 2013;Richards et al 2002;Waters-Rist et al 2011). These methodological advances have led to a proliferation of research that has begun to tease out biocultural and environmental influences on past communities and contribute to the elucidation of relationships among diet, morbidity, and mortality in various subgroups (e.g., Bourbou et al 2013;Gregoricka and Sheridan 2012;Henderson et al 2014;Kaupová et al 2014;Prowse 2011;Reitsema and Vercelloti 2012;Reitsema et al 2016;Sandberg et al 2014).…”