Isotopic and genetic analyses of a mass grave in central California: Implications for precontact hunter-gatherer warfare.

OBJECTIVES: Analysis of a mass burial of seven males at CA-ALA-554, a prehistoric site in the Amador Valley, CA, was undertaken to determine if the individuals were "locals" or "non-locals," and how they were genetically related to one another. METHODS: The study includes osteological, genetic (mtDNA), and stable (C, N, O, S) and radiogenic (Sr) isotope analyses of bone and tooth (first and third molars) samples. RESULTS: Isotopes in first molars, third molars, and bone show they spent the majority of their lives living together. They are not locals to the Amador Valley, but were recently living to the east in the San Joaquin Valley, suggesting intergroup warfare as the cause of death. The men were not maternally related, but represent at least four different matrilines. The men also changed residence as a group between age 16 and adult years. CONCLUSIONS: Isotope data suggest intergroup warfare accounts for the mass burial. Genetic data suggest the raiding party included sets of unrelated men, perhaps from different households. Generalizing from this case and others like it, we hypothesize that competition over territory was a major factor behind ancient warfare in Central California. We present a testable model of demographic expansion, wherein villages in high-population-density areas frequently fissioned, with groups of individuals moving to lower-population-density areas to establish new villages. This model is consistent with previous models of linguistic expansion.

Sex-biased parental investment and female wealth accumulation in ancient California.

OBJECTIVES: The mortuary record at Middle Period site Kalawwasa Rummeytak (CA-SCL-134) (2600-1225 cal BP) in California's southern Santa Clara Valley shows pronounced wealth inequality; Olivella shell bead wealth, as well as other grave goods, are concentrated in the burials of several older adult females. The concentration of wealth among women, along with regional strontium isotopic evidence of male-biased residential shifts in early adulthood, suggests a matrilineal kinship system that practiced matrilocal post-marital residence patterns. We suggest local resource enhancement effects incentivized keeping women in their natal communities and investing more in female offspring. MATERIALS AND METHODS: With the consent of, and in collaboration with, the Muwekma Ohlone Tribe of the San Francisco Bay Area, this paper employs isotopic analysis (δ15 N and δ13 C, 86 Sr/87 Sr) to examine duration of exclusive breastfeeding, weaning age (complete cessation of breastmilk consumption), early childhood diet, and lifetime residential mobility of individuals interred at Kalawwasa Rummeytak to test the assumption that the site inhabitants favored matrilocality and that female offspring received greater levels of investment in groups with female wealth/status attainment. First molars, third molars, and bone was sampled from 22 individuals. RESULTS: The average weaning age for females at Kalawwasa Rummeytak is 36.3 months ± 9.7 (1 SD), or just over 3 years. The average weaning age for males is 31.2 ± 7.9 months (1 SD), or about 2.6 years. Infants at the site were provisioned with supplemental foods dominated by C3 plants and terrestrial herbivores, as well as anadromous fish. After weaning, individuals consumed a diet dominated by acorns, C3 plants, and terrestrial herbivores, with periodic inclusion of anadromous fish. 30% of the sampled population of females exhibit local first molar 87 Sr/86 Sr values, suggesting that Kalawwasa Rummeytak is their natal community. None of the males interred at the site are locals. DISCUSSION: Despite the small sample size often unavoidable in archaeological contexts, we find possible female-biased parental investment strategies. Cessation of breastfeeding (weaning) was, on average, 5 months earlier for males compared to females. There are no differences between females and males in the consumption of supplemental or post-weaning foods. Strontium data suggest a flexible postmarital residence system that favored matrilocality. This may have incentivized greater investment in female offspring.