Abstract
This important new book applies optimal foraging theory and related theories from behavioral ecology. An introduction by the editors leads into eleven case studies. There follow two excellent critical reviews, by Bruce Smith and by Robert Bettinger, of the cases and of the value of behavioral ecology in dealing with early agriculture.
The case studies are uniformly impressive. They all include comprehensive discussions of fine and thorough data sets. Theory is well and reasonably applied. They do not force data into a Procrustean bed of simplistic theory.
The major theory used, optimal foraging theory, holds that organisms will maximize their returns of food per unit of time or effort. This is common sense, but mathematical applications of it yield some surprises. Bram Tucker, in the only ethnographic chapter, shows that the Mikea of Madagascar discount the future steeply, and thus prefer to gather wild plants; Bettinger notes that they cannot effectively guard their fields in any case. Kristen Gremillion does a neat job of showing why Kentuckians a few millennia ago cultivated more Iva in and near floodplains, more Chenopodium in uplands: Iva yields better, but only in floodplains, and it isn't worth hauling far if you have to carry it on your back. Kennett, Atholl Anderson, and Winterhalder show that only the “ideal free distribution” model cleanly predicts the episodic nature of Oceanic colonization; it specifies when people will respond to crowding by moving on. Other chapters add further neat insights. Several authors focus on the enormous time lag—usually millennia—between initial agriculture and actual reliance on crops for subsistence. Optimal foraging theory confirms the sensible position: it takes a long time to develop the whole crop system—domestication, storage, crop guarding, and so on—and during this time other options will pay better, in the short run, than working to develop, innovate, and intensify farming. One option not noted herein is the well-known one of burning, clearing, and cultivating to enhance productivity of wild nut trees, root crops, and the like; agriculture seems particularly slow to develop in places like California, eastern North America, and Jomon Japan, where nut trees were especially important. One may hypothesize that more effort invested in nut trees paid better than more effort invested in developing agriculture.
Evidently, agriculture was initially about manipulating location, not quantity. One did not get much (if any) more food by farming. What one got was control of the location of the food. Thus, central place foraging models are notably useful in several chapters of this book.
One paper, Mark Altenderfer's on domestication of llamas and alpacas, uses a different theory: costly signaling theory. This theory has been successfully applied to hunters (notably the Aché), who work disproportionately hard to bring home big game when they could get more by hunting small stuff. Apparently, women love men who bring home big animals, and other men are impressed and deferential. Surely, few things impress more than dragging home a mastodon. It is costly, but it sends a signal that the hunter is super-competent. Applying this to domestication, however, seems shaky. The process would be exceedingly slow and dull. Aspiring users of costly signaling theory should read Sexual Selections (2002), by Marlene Zuk, one of the leaders in the field. She discusses incisively the perils of generalizing from nonhumans to humans and vice versa.
The book is marked by some “math envy” and “biology envy,” but not to an oppressive degree. Some of the very best papers have no math and very little formal ecology. Joy McCorriston, always as sharp a mind as any in this field, explains the slow migration of agriculture to southern Arabia by traditional environmental arguments. Tim Dentan and Huw Barton show how foraging blended into agriculture in New Guinea. They do not represent it formally, yet their case is thorough and convincing.
As to “biology envy,” we do well to remember that behavioral ecology gets its theories directly or indirectly from social science, specifically microeconomics. Lotka and Volterra took their equations fairly straight from that field. In spite of some huffing about “Darwinian theory,” optimal foraging theory and its relatives come from social science, not from Darwin. They fit well with Darwinian theory, but are not derived from it.
All this said, the book does not deliver earth-shaking new findings. This is largely because it neglects many critically important variables. Some of these are part of optimal foraging theory, or can be accommodated within it. Discount rates, for instance, though extremely important, are seriously discussed only in Tucker's chapter. Storage, also, though mentioned in several articles, is surprisingly neglected except in Bettinger's commentary article. Surely, a critical—perhaps the most critical—difference between foraging and agriculture is that storage of seed is absolutely necessary for the latter. One must feel secure about immediate food reserves, and about safeguarding stored seed from weevils, rats, and thieves. (Bettinger gives a fine discussion of this last point). Storing requires a whole complex of technologies and social institutions. Storage by animals has been well studied within evolutionary ecology, so there is no excuse for neglecting it.
Social life is another problem. The case studies depend on individual rational choice theories. Both Smith and Bettinger pick this up, and advise taking more account of group dynamics, cooperative and competitive. Excellent behavioral-ecological models exist for social animals, from baboons to crows, and there have been some applications to humans (see, e.g., Sussman and Chapman 2004). Yet this whole side of evolutionary ecology is ignored in the present book. For instance, status is almost unnoted (except for Altendorfer's paper).
Farther from conventional optimal foraging theory, but still worth modeling, are matters like feasting, luxury, and medicinal value. These are hardly mentioned. Yet, we know that luxury has been a powerful boost to domestication throughout history. The only plant actually farmed in most of northern and western North America in 1492 was tobacco. It was an indulgent and a medicine, not a food. Also, it is hard to explain the exceedingly early domestication of squash and chiles in the New World and spices in the Old except as luxury or medicinal foods.
Most important of all is trade. It is obvious from any map of centers of early domestication that they are all at the centers of great trade routes—the logical crossings of routes spanning continents. The Levant, the central Andes, central Mexico, and central China have remained nodal throughout history. The Mississippi Valley and northern lowland South America, less clearcut early-agriculture centers, certainly have been nodal in trade. Only New Guinea seems anomalous, and it had the critically important salt trade; highlanders have to import salt from the coast. We also know that agriculture spread along trade routes. Unquestionably, flows of goods and information had everything to do with the rise of agriculture. I believe that people invented agriculture not to have more food, but to make sure that one had a supply of highly-valued food ready at hand and defensible. Then it was easily and quickly available for trade, feasts, ceremonies, or sheer enjoyment.
All these matters, and their effect on intensification and innovation, can be modeled within modern agricultural economic theory. Moreover, modern economics routinely models actual decision-making. This vital behavior is barely considered in behavioral ecology, because the field usually deals with creatures that allegedly act from genetically programmed instincts and do not really decide. This allegation is probably wrong for most mammals and birds, but perhaps a plausible simplification. For humans, it doesn't work. I would respectfully recommend that future users of behavioral ecology models go back to the wellspring—microeconomics—and borrow more.
Some authors are particularly over-eager to assume that food shortage is the only human motivator. Kennett, Anderson and Winterhalder, commenting on early introductions of possums, bandicoots, wallabies, and rats to islands off New Guinea, can hypothesize only “that people may have been compensating for population density-dependent resource depletion with the introduction of new species” (p. 277). Maybe, but the rats were surely stowaways, and the other animals may have been introduced because they were more profitable to hunt than abundant but scattered local foods (an idea from optimal foraging theory), or for their fur, or for ritual or ceremonial reasons, or as gourmet delicacies, or even as pets.
Data are usually excellent—thorough and accurate—but there are some strange lapses. Some authors, including Dolores Piperno (on p. 143), cite old figures for hunting that allege incredibly high return rates in calories per hour, e.g., “17,971-31,450” for “mule deer and bighorn sheep.” This would require taking an animal every couple of hours. My hunter friends would be truly envious. When one considers that a serious optimal foraging calculation would include the time spent making and repairing the necessary bows, arrows, spears, and knives, the figures become surreal. Such figures lead to distorted calculations of relative return rates.
These criticisms should not put anyone off from reading this excellent book. It proves that behavioral ecology has much to offer archaeology, especially in directing archaeologists to look soberly, seriously, and thoroughly at large and detailed data sets. The book lacks dramatic breakthroughs, but gives us sensible, well-controlled, believable papers on early agriculture. Models that rein in wild speculation, and force people to look at and improve extensive data sets, deserve to be encouraged.