Archaeologists in eastern India have found remains pointing to the existence of a highly developed urban settlement, the BBC reported on Monday. On the basis of recently completed excavations, the research team believes the city had approximately 25,000 inhabitants in the fifth century B.C. How do archaeologists estimate ancient populations?
Fieldwork and guesswork.
There's not a whole lot of detail in the article and this is one of the more problematic issues in archaeology, in part because estimating population is so crucial to so many theories. Back in the '70s an awful lot of work involved using 'population pressure' in the form of carrying capacity to try to explain why certain traits (e.g., agriculture) arose where and when they did. A lot of people were using systems theory, a purely mathematical approach which, obviously, needed numbers to work. These were especially hard to estimate in hunter-gatherer societies where you didn't have even house structures to estimate population size and you had mobility issues to deal with. Very dicey.
That was one of the reasons the New Archaeology foundered with a lot of people: Even though they had nice theories to work with (usually theories borrowed from disciplines that were working with actual, live people), they didn't have very good ways to estimate the inputs into the models. That's the trouble with borrowing theories: theory is developed in tandem with the available data sources. My favorite quote on this conundrum comes from Richard Lewontin:
If one simply cannot measure the state variables or the parameters with which the theory is constructed, or if their measurement is so laden with error that no discrimination between alternative hypotheses is possible, the theory becomes a vacuous exercise in formal logic. . .(Lewontin 1974:11)
Describes much of archaeological theorizing to a T.
Lewontin, R. C.
1974 The genetic basis of evolutionary change. Columbia University Press, New York