Breastfeeding and weaning practices of the ancestral Ohlone Indians of California: A case study using stable isotope analysis of bone collagen

Abstract

Variation in human breastfeeding and weaning practices is subject to changing social pressures and norms, as well as individual agency. This paper presents a case study from the Yukisma Mound (CA‐SCL‐38), a prehistoric site in the San Francisco Bay Area, which was used as a ceremonial and cemetery space by the ancestral Ohlone Indians between 780 and 230 cal years bp. Stable carbon and nitrogen isotope values from bone collagen of 201 individuals, including 26 subadults, are analysed. The Weaning Age Reconstruction with Nitrogen isotope analysis package in R is used to model expected δ15N values of infant bone collagen, against which measured δ15N values reveal individual variation in weaning practices. Infants from this burial sample were exclusively breastfed until approximately 0.8 years (maximum density estimation (MDE), marginal probability = 0.0456), and completely weaned by around 4.4 years (MDE, marginal probability = .0409). Range of variation in adult diets is used as a baseline of comparison, in addition to mean δ15N values of adult females, to better consider supplementary food options, and to avoid the assumption of a homogeneous maternal diet. Comparison with weaning data from contemporaneous regional sites, drawn from studies using tooth dentin of individuals who survived childhood, reveals that introduction of complementary foods and cessation of breastfeeding occurred somewhat later at the Yukisma Mound. This contrast suggests prolonged supplementation with breastmilk for children who expressed nutritional stress or disease. Variation in weaning trajectories is further interpreted using δ13C values to identify individuals with elevated δ15N values due to supplementation with high trophic level foods (e.g., freshwater fish and marine foods). Changes in weaning practices are demonstrated by comparison of this sample to ethnohistoric accounts of the Ohlone. This study provides an example of collaborative research with descendent populations and of making the most of available materials.

Coupled social and ecological change drove the historical extinction of the California grizzly bear ( Ursus arctos californicus )

“…), deer ( Odocoileus hemionus ) and livestock (goat, sheep, cow) bones, and fish muscle and fin clips (figure 2). We augmented this dataset with greater than 60 published stable isotope values for food sources from both the pre- and post-1542 time bins [21,24,40–43] (electronic supplementary material, data file). Bivariate stable isotope values ( δ 15 N and δ 13 C isotopic space) were significantly different among food categories in both eras (MRPP; pairwise comparisons followed by Benjamini–Hochberg (B-H) corrections: pre-1542 foods, all p < 0.0005; post-1542 foods, all p < 0.00002; electronic supplementary material, table S2) [44].…”

“…), deer (Odocoileus hemionus) and livestock (goat, sheep, cow) bones, and fish muscle and fin clips (figure 2). We augmented this dataset with greater than 60 published stable isotope values for food sources from both the pre-and post-1542 time bins [21,24,[40][41][42][43] (electronic supplementary material, data file).…”

The “weanling's dilemma” revisited: Evolving bodies of evidence and the problem of infant paleodietary interpretation

“…The principle of mother–infant trophic level tissue effects in breastfeeding observed for keratinized tissues have been inferred to also occur in skeletal tissues such as bone and tooth collagen. Isotope ratios plotted against age at death (e.g., Dittmann & Grupe, 2000; Fogel et al, 1989; Gardner et al, 2018; Schurr, 1997) and, more recently, age of tissue formation in dentine (e.g., Beaumont & Montgomery, 2015; Craig‐Atkins et al, 2018; Eerkens et al, 2011; Fuller et al, 2003) are used to establish infant dietary patterns of populations or individuals.…”

Stable isotope evidence of diet breadth expansion and regional dietary variation among Middle-to-Late Holocene Hunter-Gatherers of Central California

“…Stable carbon and nitrogen isotope analysis has been applied in a number of archaeological settings to examine the relative contribution of marine versus terrestrial resources to the diet (Ambrose et al, 1997;Chisholm et al, 1982Chisholm et al, , 1983Coltrain, 2009;Coltrain et al, 2004;Keegan and DeNiro, 1988;Richards and Hedges, 1999;Schoeninger et al, 1983;Walker and DeNiro, 1986). Previous isotopic research in California has focused on human paleodiets along the Santa Barbara Channel of southern California (Goldberg, 1993;Harrison and Anne Katzenberg, 2003;Walker and DeNiro, 1986), Monterey Bay (Jones, 1996;Newsome et al, 2004), the San Francisco Bay Area (Bartelink, 2009;Beasley et al, 2013;Gardner et al 2018), and the Sacramento-San Joaquin Delta region (Bartelink, 2006;Eerkens et al, 2013a).…”