| 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 d13C to document the introduction of solid foods to infant diets and d18O to monitor the decline of breastfeeding. We report enamel carbonate d13C and d18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyu´ , 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 withH3PO4 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% higher in d13C 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 d13C in childhood diets did not change systematically. First molars and premolars are similar in d18O, but third molars average 0.7% lower than first molars (P < 0.0001) and 0.5% lower than premolars (P < 0.0003). First molar and premolar d18O 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 Kaminaljuyu´ children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later.
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