Stable carbon and oxygen isotopes in human tooth enamel: Identifying breastfeeding and weaning in prehistory

Abstract

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used delta13C to document the introduction of solid foods to infant diets and delta18O to monitor the decline of breastfeeding. We report enamel carbonate delta13C and delta18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5/1000 [corrected] higher in delta13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the delta13C in childhood diets did not change systematically. First molars and premolars are similar in delta18O, but third molars average 0.7/1000 [corrected] lower than first molars (P = 0.0001) and 0.5/1000 [corrected] lower than premolars (P = 0.0003). First molar and premolar delta18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later.

Behavioral Ecology and Archaeology

“…Not all features of life history can be monitored skeletally, but two that are central to the grandmother hypothesis, age at maturity and weaning age, can be. Testing hypotheses about the former (e.g., Caspari and Lee, 2004;Dean et al, 2001;Smith, 1993) and exploring promising ways of establishing the latter (e.g., Rabb, 2005;Wright and Schwarcz, 1998) are the obvious next steps.…”

Reconstructing past subsistence patterns on Zhongba Site using stable carbon and oxygen isotopes of fossil tooth enamel

“…and their G 13 C values are independent of the water stress, having a mean G 13 C value of 12.5‰ with a restricted range of from 10‰ to 14‰ [10] . The carbon isotopes will be fractionated in the consumer tissues, resulting in positive shifts, or offsets in G 13 C values between the plants and consumers that eat them, and the fractionation factors are different depending on what tissue we analyze.…”

Oxygen isotope fractionation between apatite-bound carbonate and water determined from controlled experiments with synthetic apatites precipitated at 10–37°C

“…For samples which escaped diagenetic alteration, both carbon and oxygen isotope ratios of carbonate from apatites constitute valuable proxies of the diet, ecology and environments of many terrestrial vertebrates since the Mesozoic (e.g. Wright and Schwarcz, 1998;Kohn and Cerling, 2002;Smith et al, 2002;Zazzo et al, 2002;Jim et al, 2004;Hoppe, 2006). The record of seasonal temperature variations has been proposed on the basis of measured sinusoidal-like isotopic time series obtained from the intra-tooth sampling of hypsodont vertebrates (e.g.…”