Environmental Engineering Reference
In-Depth Information
8
Crops and Animals
The most important force driving the evolution from foraging to crop cultivation
and the domestication of animals is clear: gathering and hunting cannot support
population densities higher than about one person per square kilometer, even in
benign environments with abundant standing biomass. As the numbers of early
Holocene humans began to increase, they gradually turned to more intensive ways
of food procurement, to what are—in comparison with later traditional agricultures,
and even more so with modern farming—still rather extensive ways of growing
crops and rearing animals for meat and milk. Given the enormous variety of envi-
ronments and dominant food sources, there could be no typical population density
for foraging: the actual rates ranged over nearly two orders of magnitude, from just
one person per 100 km
2
(or 0.01/km
2
) in both densely wooded rainy tropics and
on cold boreal plains to 0.1/km
2
for hunters on tropical grasslands, all the way to
more than 1/km
2
in coastal societies relying on a rich supply (permanent or seasonal)
of marine foods (Smil 2008).
The largest forager data set, presented by Marlowe (2005), allows the following
generalizations. As expected, population densities increase with primary biomass
but level off when the phytomass reaches about 30 kg/m
2
: Marlowe's mean for the
entire sample of 340 societies is 0.25 people/km
2
, with a median of 0.11 people/km
2
(table 8.1). The highest rates (in excess of 1 person/km
2
) were among the foragers
along the northwestern Pacii c coast of North America, but their exceptional densi-
ties rel ected the seasonal abundance of anadromous salmon rather than high
habitat richness. Food shares contributed by gathering, hunting, and i shing corre-
late signii cantly with latitude: the latter two activities were dominant in high
northern latitudes and important in their southern counterparts, while gathering
was the most important contribution in the tropics and subtropics.
In contrast, the population densities of pastoralists were almost always above 1
person/km
2
even in arid grasslands, and shifting cultivation commonly supported
