Hello human ecologists. I must say, I’ve been watching this blog from afar (well, from Mexico) with a fair amount of awe at the range of material you’ve been covering. I wish I’d had a class like this! For that matter I wish all anthropologists and ecologists had a class like this.

So, here’s a bit of background for the Hamilton et al. 2007 Proc Roy Soc Lond Ser, B paper you’re reading as one of the papers this week. This paper, and its companion, Hamilton et al. 2007 PNAS 104, arose from spending a lot of time with Oskar, going to the Biocomplexity Seminar a few years ago (now defunct) and hearing week after week about metabolic scaling theory and complex biological systems. After several months of trying to get my head around what it all meant, it suddenly occurred to me that if all these simple scaling laws lead to all this emergent complexity (and simplicity) in ecological systems, due to the fundamental constraints of physics, chemistry, thermodynamics etc, then the same must be true for human systems as we too are simply another biological species making a living within complex ecosystems. That is to say, as ecosystems are structured by the flows of energy, matter, and information between organisms and their environments, and these flows lead to scaling laws and complex structures, then human systems should display the same kinds of attributes. This should be true especially for those human systems that are arguably most subject to ecological heterogeneity, hunter-gatherers.

A couple of years prior, Louis Binford (2001) had published a large volume of research on hunter-gatherers, mainly from an archaeological perspective. But in that book he included tons of data on a worldwide sample of hunter-gatherer societies (n = 339) he had compiled, including simple metrics such as population size, territory size, and group size estimates at various levels of organization, as well as all kinds of ecological and environmental variables. So I asked the question, are hunter-gatherer societies complex adaptive systems? That is, is there something about their structure at one level, some emergent property, that arises from some underlying principle that feeds-back to impact individual fitness? So the first thing I noticed was what ended up in the Royal Society paper: There is a striking geometric scaling of group size (or strictly speaking, group size frequencies) across all levels of organization, and this is a classic pattern found in all kinds of complex systems (i.e., a hierarchical, modular, self-similar branching structure). This pattern denotes statistical self-similarity, and these fractal structures are found throughout nature from metabolic networks to the structure of river basins.

The second question was then, what kind of effect could this structure have on some measure of population efficiency? But more importantly, how might I measure this? This was answered by plotting population size as a function of territory size recognizing that the area a population uses is roughly equivalent to its energy catchment area. Because the scaling relation we found was sublinear, this means that population size increases faster than energy use (territory size), so larger populations are more energetically efficient than smaller ones. Moreover, the scaling relation we found, ~3/4, was suspiciously similar to the scaling of metabolic processes found throughout living systems. Therefore, hunter-gatherer social systems seem to show signs of a “social metabolism”, for what seemed to be the same reason as other biological systems, namely a fractal-like branching distribution network.

So this sublinear scaling (~0.75) demonstrates an economy of scale in hunter-gatherer socio-economies. Note that in the Bettencourt et al. paper (very cool paper), they find similar scalings for economies of scale in urban systems, ~0.8, yet they don’t suggest a mechanism. Might we have a universal scaling law for human economies of scale, from hunter-gatherers to urban economies? Watch this space...

Marcus