Risk, Climatic Variability, and the Study of Southwestern Prehistory: An evolutionary perspective (Larson et al 1996)

Dendrocronological data for the region of the Anasazi in the Vermillion Cliffs and northern Black Mesa between 900 and 1300.

Larson et al. (1996) make two basic arguments in this paper (1) they believe that evolutionary theory holds a great deal   of promise for understanding both specific events and the overall pattern of southwestern prehistory and (2) they advocate and  approach that incorporates high-resolution dendroclimatic reconstructions of inter annual climatic variation and extreme climatic events.
Larson et al (1996) present new dendrological data consisting of the Palmer Drought Severity Index (PDSI)  reconstructions of June soil  moisture rates, which provide significant insights into the ecological and economic impacts of climate on the Anasazi of the Vermillion Cliffs and northern Black Mesa regions between A.D. 900 and 1300.

They believe a selectionist framework provides a clear theoretical rationale for focusing on climatic variability in the Southwest. They argue that the Southwest was always in risk and that the adaptation of the Anasazi people to the Vermillion Cliffs and northern Black Mesa regions was being shaped by risk conditions. Adaptive strategies included specialized agriculture, dependence on storage, and exchange of food between settlements.

The abandonment of the region implies a catastrophic failure of the adaptation shaped by the previous 400-600 years of selection-driven-evolution.

STUDY AREA

The following map presents the location of the Anasazi regions, the major drainages, geographic features, and the general location of the primary tree-ring sites

POPULATION LEVELS

Figure 2 presents a composite of the relative population reconstructions for a number of areas in the northern  Southwest. There is clear evidence of increasing populations levels, population densities, and large villages size throughout the Anasazi region over time.