The “forager population paradox”

During the 1960s and 1970s, many of us believed that hunter-gatherers, living “in a state of nature,” would have largely stationary populations, closely regulated by density dependent factors. In contrast to agricultural and industrial societies, they had not exhausted, eroded, or polluted their world. Their populations were small and sparse. We assumed they had always been that way. We may have been totally wrong.

In those days, debate centered on the processes that restrained populations. Infanticide, senilicide, birth spacing, famine, drought, and warfare were discussed. A stationary population was thought to be consonant with Deevey's (1960) and Hassan's (1978) widely cited calculations of the slow pace of increase during the Pleistocene. Hassan's papers comprise a substantial and scholarly integration of demography and archaeology that deserves more than the usual fleeting citation. In collecting and estimating the range of parameters of hunter-gatherer reproduction and mortality, Hassan (1973, p. 540) notes the incompatibility of observed hunter-gatherer fertility and mortality with a long-term stationary population. Birdsell (for example, 1968) had also noted the incompatibility of hunter-gatherer fertility and mortality with stationary populations, and he used this as one of his arguments for his view that infanticide had been a population regulation mechanism.

“Control mechanisms” of hunter-gatherer populations were proposed as society level restraints, only occasionally as results of individual practical decisions. Caldwell and Caldwell (2003) review the early phases of this history from the perspectives of demographers and anthropologists. My perspective is unashamedly biased by close exposure to the parallel debates in biology that preceded them. In biology, the theory that there were societal level restraints, mainly attributed to Wynne-Edwards (1962), was quite quickly discarded. It was discarded because natural selection would be expected to favor individuals who eschewed the restraint, who would quickly outnumber those who volunteered to restrain the number of their descendants. The short-lived debate over societal restraints was replaced by a lasting debate about whether limits were imposed by increasing population density, or by random processes such as unpredictable climatic extremes not caused by population density (although in reality, the size of their effects could be correlated with population density). In the history of animal population studies, density dependence was championed by David Lack (1954), and extrinsic factors were best known from the writings of Andrewartha and Birch (1982).