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Wednesday, November 16, 2005

Fertility Among Foragers and Agriculturalists

Now here's an interesting paper from karen kramer and james boone: Why Intensive Agriculturalists Have Higher Fertility: A Household Energy Budget Approach.

Basically Kramer and Boone look at comparative fertility rates in foraging and agricultural societies:

"It is widely held that human population growth rates began to increase markedly after the Pleistocene/Holocene transition largely as a consequence of the adoption of agriculture and sedentism. A common explanation for this increase in growth rates has been that circumstances associated with food production and/or the accompanying decrease in mobility allowed for higher fertility rates, but over the past decade a number of empirical studies and simulation analyses have revealed that the relationship between mode of subsistence and fertility is more complex than had previously been realized."

"In 1988, Campbell andWood published a cross-cultural compilation of total fertility rates (TFR) of 70 forager, horticultural, and intensive agricultural societies from the contemporary ethnographic record that showed no significant differences in TFRs across subsistence regimes. Hewlett (1991) published a similar analysis of 40 mobile and sedentary foragers and pastoralists that indicated slightly higher fertility rates among pastoralists, although the difference was not significant. In 1993, Bentley et al. published an extensive critique and reanalysis of the Campbell and Wood study, presenting a new cross-cultural comparison of 57 forager, horticultural, and intensive agricultural groups (Bentley, Jasien-ska, and Goldberg 1993, Bentley, Goldberg, and Jasienska 1993). Using a subset of the Campbell andWood sample, excluding nonindependent cases (ethnic groups that were closely related) and populations with high levels of sterility, they found that intensive agriculturalists had significantly higher fertility rates. Interestingly, however, horticulturalists showed slightly lower fertility than foragers in the sample, although the difference was not significant. Using a similar kind of data base, Sellen and Mace (1997) have shown that for every 10%increase in dependence on agriculture there is a 0.4 increase in TFR."

Now a number of points seem to clearly stand out here. Firstly, fertility generally in foraging (hunter/gatherer) societies is not especially high: Hewlett finds a mean TFR of 5.6 with a range of 3.5 - 7.9, while Bentley, Goldberg, and Jasienska find a mean for agriculturalists of 6.6 with a range of 3.5 to 9.9. So fertility in agricultural societies is somewhat higher, now why the difference? Now as Kramer and Boone state circumstances associated with food production and/or the accompanying decrease in mobility might have been thought to account for the difference, but apparently not. So what was it?

"This paper explores the idea that children’s contribution to underwriting the cost of large families may be an important factor conditioning variation in family size and the higher fertility attained by at least some intensive agriculturalists."

In other words it was the role of children as a source of cheap labour which drove the additional fertility. Well, what'd'yu know. Definitely worth a read.