As you have likely heard, sometime over the past week the world’s estimated population crossed the 7 billion mark. This follows less than 15 years after passing the 6 billion mark, and means the world’s population has doubled over a time span of roughly 40 years. On a larger scale, the world’s population has increased by more than three orders of magnitude over the past 10,000 years or so. Courtesy of wikipedia, here is a graph of the world’s estimated population going back 12,000 years (N.B. log scale)
There are a lot of fascinating questions embedded within this graph, not the least of which is what has been and will be the evolutionary impact of this massive change in human demography. Gregory Cochran and Henry Harpending have a recent book on the topic, and John Hawks and colleagues have a PNAS article going back to 2007 on the acceleration in human evolution (as measured by the amount of selection on the human genome) as a result of the massive population expansion (Hawks has much more on the topic on his blog, here).
I think demography is a hugely important topic in studies of human evolution. At the very least, the last 3 million years of human evolution have been characterized by at least two huge demographic transitions. The first, probably dating back to the origin of the genus Homo, involved an ecological shift towards a technologically mediated gathering/hunting strategy. This, while it likely did not involve large population expansion, did probably result in significant changes to human social structures and group organization. The larger demographic change is the one that began right around the left edge of the graph above and is still ongoing – the human shift towards sedentary, densely populated settings enabled by a radical shift in how we extract food out of the environment (i.e. the domestication of plants and animals, eventually leading towards farming). These changes have important implications for the human adaptive landscape and the shape and trajectory of human evolutionary change.
Demography was once at the core of anthropological work. Early ethnographers were some of the first demographers of the planet, as an important part of ethnographic field was often a careful assessment of local demography (How many people live in a place? How are they related? How do they relate to each other? How do they move about their community/region? How many children do they have? What jobs do they do?). As ethnography moved away from a focus on studying the “other” to more nuanced questions about human existence and as the reality of how complex human demographic patterns are, even in small-scale societies, this part of ethnography was largely abandoned. Meanwhile the focus on paleodemography in archaeological and physical anthropology also stagnated as the realization that the obstacles in using biased samples of data (preserved and recovered archaeological and skeletal samples) were quite massive.
I think we are going to see a revival of demographic interest, at least within the paleo side of things, largely because of new genetic data. The ability to extract information about past human populations through the DNA of living people and ancient DNA recovered from skeletal and fossil material has opened up a new window on our demographic past. Importantly, these data provide interesting compliments to the kinds of data we already have (archaeological, skeletal, climatic) and allow for cross-testing of hypotheses.
Again, this is something I will be writing much more about in the future…so this is just a timely teaser at the moment.
UPDATE: For a take on the challenges facing contemporary anthropological demography, largely from a ethnographic viewpoint, see this 2007 paper by Jennifer Johnson-Hanks
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1. John Hawks, Eric T. Wang, Gregory M. Cochran, Henry C. Harpending, and Robert K. Moyzis, Recent acceleration of human adaptive evolution. PNAS 2007 104 (52) 20753-20758; doi:10.1073/pnas.0707650104
2. Jennifer Johnson-Hanks, What kind of theory for anthropological demography? DEMOGRAPHIC RESEARCH, Vol. 16, 1-26. http://www.demographic-research.org/Volumes/Vol16/1/; DOI: 10.4054/DemRes.2007.16.1
