1.  Introduction

Population growth in the upper end of the Etla valley appears to have been slow and steady during the Espiridión, Tierra Largas, San José, Guadalupe and Rosario phases (roughly 1600 to 500 BC).  If we suppose the archaic population of the valley to have been about 200, this corresponds to an average population growth rate of about 1.6 persons per year.  At the end of the Rosario phase (about 500 BC), when the population of the San José Mogote cluster was around 2,000, there occurred a sudden geographical shift in population with the founding of a new settlement on the top of the hill now known as Monte Albán.  There is also, possibly, some evidence for a corresponding decline in population at San José Mogote.  At the new Monte Albán settlement the population grew very rapidly to over 5,000 in the next century, a rate of more than 30 persons per year.  Over the following two hundred years, the population grew to over 17,000 by 200 BC, a rate of 60 persons per year, towards the end of the Monte Albán I epoch.  These rates of population growth are perhaps better expressed as a percentage of the mean population over the period, yielding values of 0.15, 0.86 and 0.55 percent per year over the three time ranges.  Clearly there was a major surge in population around 500BC.  Further increase in population occurred later with the advent of the Monte Albán II epoch [[*** more to come ***]].

During the first of these periods (1600-500 BC) there was a gradual shift from a nomadic, hunting and gathering existence to a more settled, small village culture with a growing dependence upon agriculture.  There is some evidence for the beginnings of social stratification towards the end of this period, but hardly sufficient differentiation to support the emergence of a chiefdom.  The archaeological evidence suggests that as families clustered together there was a tendency for one family to occupy a slightly larger house, perhaps in a slightly more prominent position [ref.].  There is also some evidence for the construction of common or public buildings towards the end of the period [ref.].

With the move to (or settlement of) Monte Albán it appears that social stratification increased considerably and resulted in the creation of a chiefdom in which one family or small group of people could demand labor from others.  The hill at Monte Albán is without any natural supply of water in the long dry season, and it is difficult to envisage a group of socially equivalent families settling there in full awareness of the daily need to fetch water from the valley over 300 meters below.  On the other hand it is easy to see a dominent family emphasising their superior social status by a prominent residence, and demanding the provision of water and food as a service from sub-servient people.

While this desire for emphasis of social status might explain the move to a prominent hill site, it still remains to be explained why the population surged upwards so quickly (describing it as a population explosion would not be an exageration).

The move to Monte Albán has been considered as synoikism under the pressure of an (unidentified) external threat [ref. needed], but this leaves us with a contradiction between a rapidly expanding population (an indication of “good” times with plentiful resources and little external threat) and a population under a sufficiently severe external threat to force a move to a defensible site with fewer resources (conditions of fewer immediate resources and, presumably, increased deaths by warfare).  No sufficiently major external threat has been identified, and sporadic raiding by neighbouring small Mixtec bands hardly seems to be sufficient cause for the major upheaval of the move to Monte Albán.  Indeed the available evidence strongly supports the idea that the major aggressor in the Oaxaca valley at the time would be the San José Mogote population itself.  Against the external threat hypothesis is the evidence that the construction of extensive defensive works at Monte Albán did not occur until at least 200 years after the initial occupation of the site [ref. needed].

An alternative explanation for synoikism is the desire for political aggrandisement with accompanying growth of public building and expansion of territorial control, and the move to Monte Albán was indeed eventually accompanied by both.  Nevertheless, the question remains:  why undertake a difficult, expensive and disruptive move from a site in first class agricultral land to a remote and arid mountain top?  Why not remain in San José Mogote and emphasise social superiority by building on a larger and higher platform?  And surely, a disruptive move would inhibit rather than encourage population growth.  One possibility which has not, as far as I am aware, been considered is that Monte Albán was settled by a rebellious splinter group from San José Mogote.  This suggestion would be consistent with the continued existence and later growth of San José Mogote alongside Monte Albán, and provide the initial driving force for a move to a previously unpopulated (and agriculturally unattractive) site.  Conceivably the San José Mogote chiefdom was strong enough to expell a subversive element, and one can then understand why they were left alone for a considerable time (they are no threat, we have expelled them to an arid site in a foreign area which has been described as a “buffer zone” [ref. needed]).

Leaving aside all speculation about causes of the move and the subsequent rapid population growth, the population figures themselves can yield evidence for the influence of external factors on population growth.  A community effectively isolated from external or internal threats, and not experiencing any new technology (e.g. in agriculture) might be expected to increase its population slowly and steadily.  A community suddenly exposed to severe external threat (warfare) should exhibit a slowing down of population growth, whilst one suddenly acquiring new, more productive agricultural technolgy would be expected to show a sudden surge in population.  Conversely, if we can find evidence of a time when either growth inhibition or acceleration occurred, we can infer that the population was then experiencing a major change in its circumstances.

The population estimates available in the literature are sparse and by themselves insufficient to support any continuous timewise evolution of the population during Monte Albán I.  There has long been significant scientific interest in population growth in general, and models have been proposed to fit/explain the observed growth, fluctuations and collapse of many species [some general ref. needed].  In this paper we consider the application of some of the simpler models for population evolution to the question of population growth at Monte Albán, with the aim of proposing a model for a continuous time evolution of population from which we might make inferences about changes in political or environmental factors affecting the population at Monte Albán.