Were humans under the same constraint? Obviously Malthus must have thought that effective control was not yet in place, and from his perspective it was only going to get worse. He was correct given the subsequent unfolding of major events in human history, such as the Industrial Revolution, that led to high concentrations of people living in crowded, unsanitary cities.
However, looking over the long course of human history, now reckoned in terms of several million years, foraging populations lived in small, scattered groups, and local pressures on resources could be relieved temporarily at least through out-migration. In fact, it is quite likely that movements of precursor human groups within and between continents in early time periods were in part due to successful cultural and biological adaptation and reproduction. Population growth spurred outward expansion.
A clear picture of the number and timing of migrations has not yet emerged. One intriguing notion is that there was a major population bottleneck some hundreds of thousands of years ago, when it is projected that the source population from which all of present-day humans stem consisted of only 10,000 adults (Harpending, Sherry, Rogers, & Stoneking, 1993). It was from this base in Africa that principal migrations populated Eurasia. If this conjecture holds up under continued examination, then it would appear that population control for the human species did conform to natural evolutionary processes until relatively recently. Early human groups were subjected to the same kinds of adversities as other animals, that is, "struggles for existence," in the form of food and shelter shortages, some degree of predation, injuries and deaths from accidents, natural calamities, etc. However, there also was a growing advantage and environmental buffering in the form of cultural adaptation and evolution that would have begun making its impact. Cultural development along lines of improved tool-making technologies and more complex social organization, which may have been biologically grounded in brain evolution, provided the means of dispersal and also the capability of replacing or displacing earlier established precursor humans (Stringer, 1994). An alternative view is that the latest wave of human migrants interbred with some of the existing groups, and these subsequently evolved into modern Homo sapiens (Wolpoff & Caspari, 1997). It might be noted that within the scenario of population replacement, and to the extent that this action was intentional and confrontational, this possibly would represent the first instance of population control in human history whereby earlier inhabitants became extinct. The final version on this aspect of human history is yet to be written, however.
Picking up the story around tens of thousands of years ago, humans at that point had managed to disperse throughout all of the areas of their current distribution, in what some have conjectured to be a period of explosive population growth. For instance, Sherry et al. (1994), using mtDNA estimates, base the timing of this spectacular growth in the 40,000 to 60,000 year range, seemingly coinciding with major new cultural developments (Klein, 2000). Total world population size at this time could run into millions of individuals, which would be a rather remarkable recovery following the presumed bottleneck noted above. While there may have been local checks on population, such as periodic episodes of high mortality due to natural calamity and starvation (infectious disease would not likely to be present at this time because of the small groups and their scattered, intermittent contacts), the principal population dynamics seem to have involved high levels of reproduction followed by population expansion, that is, migration based on necessity and opportunity. To be sure, early, partially effective forms of birth control were probably being practiced, and these will be discussed shortly.
This picture of relatively small, mobile groups subsisting on a mixed foraging/hunting strategy characterizes much of human history. It was not until population density reached a critical mass, either through abundant local resources such as in certain riverine or coastal environments or through the development of plant and animal domestication (the "agricultural revolution" and associated market systems that brought large numbers of people together on a regular basis), that highly contagious and parasitic diseases found densely populated regions to be maintained and spread, and thereby exert death control on population growth. It can be conjectured that death control via infectious agents did occur during the past several thousand years of human history, but it was not until the Middle Ages that more precise accounting was done. For example, it is estimated that one third of the European population died during the bubonic plague ("Black Death") of the latter half of the 14th century, a catastrophe from which it did not recover until the mid-16th century (Livi-Bacci, 2001). Considering a more recent episode, it is reported that up to 500 million people died from smallpox epidemics during the 20th century (CBSHealthWatch, 2001). However, a large question does remain as to what long-lasting effect infectious disease, or any form of disease for that matter, has had on the overall growth of the human population? (The same question will be addressed later with respect to warfare.) Given the complete recovery of numbers following the cited events, and other similar epidemics, it can be argued that if there was any effect it has been for fairly restricted areas and only for relatively brief periods of time.
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