| Abstract: |
Migration may have powerful effects on population growth, but it does not appear to leave distinct signature on age-at-death distributions. Its effects are identical to those of altered bith rates. Uniformitarian models are based on the assumption that observed regularities of human and mammalian biology- for example, basic age patterns of birth, death, or sexual maturation- also characterize prehistoric human populations. The basic assumption of uniformitarian approaches is that human demographic performance is contrained by a number of biological factors: length of the human lifespan, reproductive span, gestational length, and usual ages of sexual maturation. \bResults\b The actual effect of migration on skeletal age-at-death distributions is an increase in the proportion of infant deaths, a decrease in the proportion of senescent deaths, and an overall decrease in the mean age-at-death. This is precisely the same effect that increasing the fertility rate would have on the same distribution. Migration, at least in the age patterns outlined here, leaves no unique signature on the skeletal record. Therefore, the major effect of in-migrants on a death distribution is not through their mortality, but through their fertility. The addition of migrants raises crude birth rates (even if overal fertility rates remain constant) and increases the population growth rate, therefore raising the number of infant deaths and lowering the mean age-at-death. In-migration acelerates growth in two ways: through the influx of the migrants themselves and through increased crude birth rates.
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