3.4. Enamel Defects as Indicators of Stress in Past Human Populations

In general terms, any perturbing condition external to the organism that is capable of eliciting a physiological response represents a stressor agent (Selye, 1973; Little, 1983). When the threshold of susceptibility - variable from individual to individual and between populations - is reached/surpassed (for the 'hidden heterogeneity' concept, see Wood et al., 1992), the stress causes a deviation from homeostasis, and the individual/population response will result in either the successful restoration of homeostasis (adaptation) or the failure to do so (maladaptation) (Ortner, 1983; Goodman et al., 1988). From this perspective, death may be seen as the ultimate measure of maladaptation (Armelagos et al., 1981).

In skeletal populations, which theoretically provide 'natural laboratories for testing hypotheses concerning the evolution and ecology of human disease' (Duray, 1996: 275), directionality, quality, intensity, and chronology of the stress events experienced (and recovered from) during growth may be at least partially 'measured' through their effects (physiological disruptions) on dental and bone tissues (Martin et al., 1985), whereas signs (stress markers) of more subtle disruptions can be revealed at the microstructural level (Goodman et al., 1984, 1988).

Nevertheless, in addition to methodological problems (theoretically resolvable) inherent in the hierarchy of information extracted from osteodental remains, the epidemiological interpretation of such information is affected by numerous implicit limiting factors (see Cook and Buikstra, 1979; Wood et al., 1992; Tucker, 1994).

In paleobiological studies, by definition, each age class considered is actually represented by deceased individuals. Moreover, in the majority of cases, legitimate doubts exist concerning the quality and representativeness of the sample itself, independent of sample size (Macchiarelli and Salvadei, 1994). The health status assessment of a skeletal population cannot, therefore, exclude from consideration the age (and sex) composition of the sample investigated (Macchiarelli and Salvadei, 1989) and, when possible, should also consider the environmental, biocultural, and chronological context. In order to reduce the risk of misleading conclusions, these factors represent a theoretical/methodological constraint in comparisons between data derived from the analysis of samples from diverse chronological and geographical contexts.

Although the 'tools' available to the paleobiologist are usually inadequate with respect to the complexity and variability of the physiological and pathological processes investigated, enamel microdefects undoubtedly constitute one of the most effective indicators due to the capacity of dental tissue to register stress events (Goodman et al., 1980, 1984; Blakey and Armelagos, 1985; Rose et al., 1985). Further, dental crowns usually represent the most abundant remains recovered from archaeological context, and once formed, enamel 'undergoes little biological turnover and, after death, it can remain stable for long periods' (Hillier and Craig, 1992: 384). Nevertheless, in the case of archaeological populations, this paleoepidemiological 'tool' must be used with caution.

Rather than accurately representing the age class they belonged to in the living population, (most of) the infant-juvenile segment of a skeletal sample represents disadvantaged individuals who did not survive to adulthood. In the majority of cases (but, realistically, not in all), this subset is composed of individuals from the community with a lower threshold of susceptibility to stressors, thus representing a 'selected biased sample' (Wood et al., 1992). Consequently, the results obtained from the quantitative analysis of the microdefects of the primary dentition of an infant-juvenile skeletal sample must adequately consider these constraints (in addition to those strictly linked to the specific age-at-death composition of the sample investigated), and can not be used tout court in comparisons with other samples. For this reason (but also for the usual underrepresentativeness of infant and juvenile remains from archaeological contexts), most research is traditionally based on the analysis of permanent teeth, drawn from those individuals who survived to adulthood, as they represent those sufficiently robust to survive childhood (Wright, 1997).

In order to get a reasonably realistic picture of the health status of the inhabitants from Portus Romae and to reconstruct, where possible, the diachronic history of the stresses experienced (and recovered from) during growth, we are conducting systematic histomorphometric analysis of: a) the deciduous teeth of infants and juveniles; b) the deciduous teeth retained in adult dentitions; c) the permanent teeth of subadults; and d) the permanent teeth of adults.

Cited References

Armelagos G.J., Jacobs K.H., Martin D.L. (1981) Death and demography in prehistoric Sudanese Nubia. In (S.C. Humphreys & H. King, eds.) Mortality and Immortality. The Anthropology and Archaeology of Death. London: Academic Press, pp. 33-57.

Blakey M.L., Armelagos G.J. (1985) Deciduous enamel defects in prehistoric Americans from Dickson Mound: prenatal and postnatal stress. American Journal of Physical Anthropology, 66: 371-380.

Cook D.C., Buikstra J.E. (1979) Health and differential survival in prehistoric populations: prenatal dental defects. American Journal of Physical Anthropology, 51: 649-664.

Duray S.M. (1996) Dental indicators of stress and reduced age at death in prehistoric native Americans. American Journal of Physical Anthropology, 99: 275-286.

Goodman A.H., Armelagos G.J., Rose J.C. (1980) Enamel hypoplasias as indicators of stress in three prehistoric populations from Illinois. Human Biology, 52: 515-528.

Goodman A.H., Martin D.L., Armelagos G.J., Clark G. (1984) Indications of stress from bone and teeth. In (M.N. Cohen & G.J. Armelagos, eds.) Paleopathology at the Origins of Agriculture. Orlando: Academic Press, pp. 13-49.

Goodman A.H., Thomas R.B., Swedlund A.C., Armelagos G.J. (1988) Biocultural perspectives on stress in prehistoric, historical, and contemporary population research. Yearbook of Physical Anthropology, 31: 169-202.

Hillier R.J., Craig G.T. (1992) Human dental enamel in the determination of health patterns in children. Journal of Paleopathology, Monographic Publications, 2: 381-390.

Little M.A. (1983) An overview of adaptation. In (R. Dyson-Hudson & M.A. Little, eds.) Rethinking Human Adaptation: Biological and Cultural Models. Boulder: Westview, pp. 137-148.

Macchiarelli R., Salvadei L. (1989) Early Medieval human skeletons from the thermae of Venosa, Italy. Skeletal biology and life stresses in a group presumably inhumed following an epidemic. Rivista di Antropologia, 67: 105-128.

Macchiarelli R., Salvadei L. (1994) Paleodemography and selective funerary practices at Latium vetus, middle-Tyrrhenian Italy. Anthropologischer Anzeiger, 52: 37-52.

Martin D.L., Goodman A.H., Armelagos G.J. (1985) Skeletal pathologies as indicators of quality and quantity of diet. In (R.I. Gilbert & J.H. Mielke, eds.) The Analysis of Prehistoric Diets. Orlando: Academic Press, pp. 227-279.

Ortner D.J., ed. (1983) How Humans Adapt. A Biocultural Odyssey. Washington: Smithsonian Institution.

Rose J.C., Condon K.W., Goodman A.H. (1985) Diet and dentition: developmental disturbances. In (R.I. Gilbert & J. Mielke, eds.) The Analysis of Prehistoric Diets. Orlando: Academic Press, pp. 281-305.

Selye H. (1973) The evolution of the stress concept. American Scientist, 61: 692-699.

Tucker T.L. (1994) The histological evaluation of the Libben subadult dentition: an examination of mortality selection. American Journal of Physical Anthropology, suppl. 18: 198 (abstract).

Wood J.W., Milner G.R., Harpending H.C., Weiss K.M. (1992) The osteological paradox. Current Anthropology, 33: 343-370.

Wright L.E. (1997) Intertooth patterns of hypoplasia expression: implications for childhood health in the classic Maya collapse. American Journal of Physical Anthropology, 102: 233-247.