Agriculture and Property

One of the big questions in the study of ancient human history is, How did agriculture become the main technique humans use to produce food? For thousands if not millions of years, humans gathered food and hunted game to survive; some populations still live this way, as do our surviving ape cousins. To the neophyte, farming might seem like an obvious improvement over hunting and gathering (hereafter, foraging), but it turns out this isn't true. Getting started with agriculture is costly and risky, so how did it happen?

Science has attempted to grapple with this dilemma for decades, and some compelling theories have been developed to grapple with this question. Samuel Bowles' most recent publication in PNAS may be the best original research on the subject in a long time. I'm familiar with Bowles' other work, and I am regularly impressed with the rigor of his models, even if I don't always agree with all of his conclusions. It helps that he is an excellent writer because this isn't the easiest material to make accessible.

In this paper, Bowles and coauthor Jung-Kyuu Choi have built a model, on a foundation of empirical data (archaeological, climatic, and anthropological), which seeks to explain the emergence of agriculture in conjunction with the private property rights. Paleoanthropologists have previously suggested that strict property rights, generally unknown in forager societies, would be necessary for farming to become practical. But, it is difficult to explain why property rights would come into existence because, as with agriculture, there are many disincentives for foragers to adopt property rights. According the authors' model, agriculture and property coevolved: each adaptation is the key to the survival and propagation of the other.

Bowles is an economist by training, so he uses models, agent-based simulations, and game theory to validate his hypothesis. There is a particular brand of game theory called evolutionary game theory which was created to cope with just the sort of questions that Bowles routinely attempts to tackle. The best known evolutionary game theory game is the Hawk Dove game, which demonstrates how two populations of the same species which behave in seemingly irreconcilable ways manage to coexist, in what is known as an Evolutionary Stable Strategy (ESS) situation.

Like so many before them, the authors' adapt the classic Dove Hawk game to fit their needs. Instead of Doves and Hawks, the authors use Sharers, Bourgeois, and Civics. A Sharer's strategy (like a Dove's) is to split a resource by default, but if another individual claims that resource, the Sharer will give all of it up. The Bourgeois is the type that will claim all of resource if possible, contesting if necessary and appropriate (similar to a Hawk). Civics act exactly like Sharers, but if they go up against a Bourgeois, they will band together with other Civics to contest a Bourgeois trying to take the resource. These strategies are modeled on anthropological studies of extant human societies.

Thanks to the power of modern computers and the Monte Carlo engine, the authors can vary other variables as well, such as whether or not property rights are recognized among the populations. If the resource is foraged then ownership is not easily demarcated, and Bourgeois agents will go after it. But if a resource is farmed, then property rights are easily recognized because it is obvious who produced the resource and thus who it belongs to. Bourgeois won't go after these resources; they respect property rights when they are apparent. Additionally, the authors varied climate conditions and simulated inter-group competitions on top of the usual intra-group contests.

After determining all the variables and running the simulations, the authors looked for what combination of conditions create novel ESS situations, with an eye for Bourgeois dominated scenarios since their behavior is the norm for agricultural cultures. A mixed population of Sharers and Bourgeois (but no Civics) forms a steady state, but if you don't have property rights established, Bourgeois have a strong tendency to fight with each other over resources that have no clear owner, which reduces the success of the population. However, if property rights exist, the Bourgeois don't squabble amongst themselves so much, and an all Bourgeois population becomes a stable possibility.

So far the authors have shown that their premises can be incorporated into a model that appears plausible, but does it match the historical facts? A challenge for researchers trying to model early modern human development is matching simulated data with the archaeological record. When we go this far back in time, archaeological evidence is often scarce and difficult to interpret. While agriculture leaves a clear mark on archaeological record, the same is not true for property rights, and there isn't much that anyone can do about that. We just have to make do with what we've got.The authors make do quite nicely. By throwing the Holocene environmental conditions into the mix, they find that

"in the simulations, as in the archaeological record, mixed farming and hunting–gathering is the norm over very long periods, and that the process of transition when it occurred was prolonged, highly varied, and sometimes halting." 

On the other hand,

"the chicken-and-egg problem of farming and private property in our model explains why the transition was a very unlikely event, occurring in only 31 of 1,000 metapopulations that we simulated."

Yet, to me the most striking result is that their model reliably displays the Natufian culture, the first sedentary humans, and possibly the first farmers.

To wrap things up, the authors make some important points about the role of invention in early culture:

"In many histories of technology, the key event is the invention; the subsequent spread occurs inexorably as the result of its superiority in lessening the toil required to sustain life. This model has been suggested for the Holocene revolution; but it does not work. No invention was necessary."

And so, thanks to an agreeable climate, coincident evolution of farming and property right, and well, the human capacity for cultural learning, our ancestors were able to transform from foragers into farmers. Probably. Maybe. We'll have to see what the expert critics have to say in the coming months and years.

This is a great paper. I think that it may have far a reaching influence, so if you're at all interested in the ideas, have a crack at it yourself. It is not terribly long, and quite accessible.

Bowles, S., & Choi, J. (2013). Coevolution of farming and private property during the early Holocene Proceedings of the National Academy of Sciences, 110 (22), 8830-8835 DOI: 10.1073/pnas.1212149110