Richard R. Paine

If a population crashes in prehistory, and there is no paleodemographer there to hear it, does it make a sound?

Catastrophic episodes (e.g., epidemics, natural disasters) strike with only limited regard for age. A large percentage of catastrophic mortality in a population can lead to a death distribution that resembles the living distribution, which includes greater numbers of older children, adolescents, and young adults than typical mortality profiles. This paper examines both the population implications of a large catastrophic mortality event, based on the Black Death as it ravaged medieval Europe, and its long-term effects on age-at-death distributions. An increased prevalence of epidemic disease is a common feature of reconstructions of the shift to agriculture and the rise of urban centers. The model begins with a hypothetical Medieval living population. This population is stable and characterized by slow growth. It has fertility and mortality rates consistent with a natural-fertility, agrarian population. The effects of catastrophic episodes are simulated by projecting the model population and subjecting it to one large (30% mortality) catastrophic episode as part of a 100-year population projection. A pair of Leslie matrices forms the basis of the projection. The catastrophic episode has important, long-term effects on both the living population and the cumulative distribution of death. The living population fails to recover from plague losses; at the end of the projection, population is still less than 75% its pre-plague level. The age-at-death distribution takes on the juvenile-young adult-heavy profile characteristic of many archaeological samples. The cumulative death profile based on the projection differs from that produced by the stable model significantly (P < 0.05) for 25-50 years after the plague episode, depending on sample size.

Effect of Sample Bias on Paleodemographic Fertility Estimates

Paleodemographers must work to understand how representative any archaeologically recovered skeletal series is and the potential effects of series bias on their demographic reconstructions. We examine two forms of bias: 1) infant underenumeration caused by differential preservation or incomplete archaeological recovery and 2) the underenumeration of individuals over age 45 related to methodological bias. We generated 60 simulated skeletal series of 250 individuals each based on the Brass ([1971] Biological Aspects of Demography (London: Taylor and Francis), pp. 69-110) logit models. In the first test, age bias was introduced deterministically for all individuals with age at death over 40 years using the Lovejoy et al. ([1985] Am. J. Phys. Anthropol. 68:1-14) bias estimates. In the second test, 50% of all individuals under 5 years old were removed from each simulated distribution. The simulated series were analyzed using the model life table fitting procedure developed by the authors (Milner et al. [1989] Am. J. Phys. Anthropol. 80:49-58; Paine [1989] Am. J. Phys. Anthropol. 79:51-62). Forms of adult age estimation bias described by Lovejoy and coworkers inflate estimates by 10-20% of the true crude birth rate (CBR) (the number of births per year per 1,000 population). Overestimation of fertility and birth rates increases both absolutely and as a percentage of the true rate as population growth increases. This bias is very consistent. Because Lovejoy and colleagues have estimated the methodological bias itself, its effects can be estimated. Infant underenumeration is a more serious obstacle. It is not presently possible to estimate infant underenumeration reliably without prior knowledge of fertility rates. This reduces fertility reconstructions based on infant-biased samples to minimum fertility estimates.

Environmental Degradation and the Classic Maya Collapse at Copan, Honduras ( a.d . 600–1250): Evidence From Studies of Household Survival

The Late Classic Maya abandonment of the Copan Valley, Honduras, began in the ninth century a.d . and lasted approximately 250–300 years. The relationship between local ecological setting and residential group abandonment is examined by applying event-history analysis to the known occupation spans of 140 residential mound groups, dated by obsidian hydration. Late Classic households in ecologically vulnerable sections of the Copan Valley—as measured by slope, soil type, and natural vegetation—had significantly higher risk of abandonment than households in more ecologically stable settings. Abandonment risk rises sharply in all regions at the end of the seventh century a.d . Both computerized agricultural simulations and settlement demographic reconstructions indicate that increased levels of agricultural intensification necessary to meet the subsistence needs of Copans growing population would have led to large-scale erosion in upland areas and a significant reduction of soil fertility in all regions of the valley at that time. Mound-group abandonment patterns tend to support the hypothesis that environmental degradation played a dominant role in the collapse of the Copan polity.

Assessing the reliability of paleodemographic fertility estimators using simulated skeletal distributions

The reliability of published paleodemographic fertility reconstruction methods was assessed using simulated age-at-death distributions and a published cemetery series from a population with known birth rates. In the first test, the Brass ([1971] Biological Aspects of Demography, pp. 69-110) LOGIT models were used to generate 180 simulated skeletal samples of various sizes (N = 50, 100, 250) from hypothetical populations with known demographic rates. The base populations were expanding (r = 0.01), stationary, or declining (r = -0.01), yet all had the same life expectancy. Growth differences resulted from different fertility rates. The simulated skeletal series were then analyzed using the model life table fitting procedure outlined by Paine ([1989a] Am. J. Phys. Anthropol. 79:51-62), three commonly employed age ratio tests (Bocquet-Appel and Masset [1892] J. Hum. Evol. 11:321-333; Buikstra et al. [1986] Am. Antiquity 51:528-546), and one age-at-death ratio not previously published. In the second test the model life table fitting procedure was used to estimate fertility for a historical population, the Newton Plantation, Barbados (Corruccini et al. [1989] Am. Antiquity 54:609-614), with known demographic characteristics.