The Sociobiology of Domestication

Abstract

Farming, whereby one organism cultivates a population of another organism, is usually associated with tending of livestock and crop plants by humans. However, similar behavior exists in other organisms, and those examples predate human agriculture by millions of years. The best-known examples of nonhuman farming are the fungus-farming insects (Mueller et al. 2005). In this chapter we use a broader concept of farming, including mutualistic host-symbiont relationships in general, and ask how useful this concept is for analyzing their evolution. The host in a mutualistic host-symbiont interaction has the same interest as a farmer who cultivates a field of rice or breeds a herd of cattle-namely, maximizing the productivity of its domesticates. Simply put, farmers can be considered as hosts and their crops and livestock as symbionts. Collective performance of the symbionts usually depends on cooperation (Frank 1996). However, within a group of symbionts a "tragedy of the commons" (Hardin 1968) may occur: individuals within the herd may increase their relative fitness within the group at the cost of collective herd productivity (see chapter 3, this volume). This is a fundamental problem of social evolution in a wide variety of biological (and socioeconomic) interactions, ranging from the eukaryotic cell with thousands of mitochondrial genomes, to natural populations of plants or animals, to the farmer with thousands of livestock. Because of the difference in numbers between partners, domestication, defined as the genetic modification of one species by another in ways that benefit the modifying species but that would reduce the fitness of the modified species in its original niche, is essentially a process of social evolution. How is lower-level competition within the herd prevented from disrupting collective performance, and thus herd productivity? First, we review the data from a variety of natural host-symbiont interactions and identify key mechanisms that hosts use to enforce sociality in their livestock. Second, we consider human agriculture and husbandry and identify parallels with nonhuman host-symbiont interactions. We also identify examples of conscious or unconscious group selection of domesticated species by farmers and of unwanted consequences of selection at the level of the individual. Third, we identify opportunities for group selection. While the conditions for selection for cooperation in nature are highly specific and rare, humans can create those conditions in their selection programs and be inspired by natural examples of host-symbiont interactions. Explicitly considering social effects in artificial selection is