The territorial foundations of human property

Abstract

Many animal species have morphological and cognitive adaptations for fighting with others to gain resources, but it remains unclear how humans make fighting decisions. Non-human animals adaptively calibrate fighting behavior to ecological variables such as resource quantity and resource distribution. Also, many species reduce fighting costs by resolving disputes based on power asymmetries or conventions. Here we show that humans apply an ownership convention in response to the problem of costly fighting. We designed a virtual environment where participants, acting as avatars, could forage and fight for electronic food items (convertible to cash). In two experimental conditions, resources were distributed uniformly or clustered in patches. In the patchy condition, we observed an ownership convention — the avatar who arrives first is more likely to win — but in the uniform condition, where costly fights are rare, the ownership convention is absent.

Introduction

Many animals make nuanced and adaptive decisions about whether, and how intensely, to fight others to secure resources such as territory, food or mates (Brown, 1964, Kokko et al., 2006, Maher and Lott, 2000, Maynard Smith, 1982, Parker, 1974). Research on territoriality has found that decisions about whether to fight are sensitive to as many as 20 ecological variables, including resource quantity, resource distribution, population density and predation levels (Maher & Lott, 2000). Research on animal contests has discovered that animals use strategies to reduce the costs of disputes such as fighting assessment (Parker, 1974) and conventions (Maynard Smith, 1982). However, despite a large literature on fighting in non-human animals — including mammals, birds, fish and insects — little is known about how humans make fighting decisions.

Several scholars have applied theories from biology to understand how humans secure resources, deriving novel conclusions relevant to economics and property law (Gintis, 2007, Krier, 2009, Stake, 2004). These accounts particularly draw on Maynard Smith's (1982) concept of a fighting convention or an “uncorrelated asymmetry” in which animal fights are resolved based on an asymmetry that is uncorrelated with fighting ability. Maynard Smith's analysis led to the counterintuitive conclusion that animal fights can be more than battles of brawn: choosing whether to fight or flee based on a conventional asymmetry, such as prior possession, can be an evolutionarily stable strategy (ESS) because individuals thereby reduce fighting costs relative to others who ignore the convention (Maynard Smith, 1982). In humans, resource disputes are decided by more than sheer power and, hence, the strategic convention model could potentially explain the foundations of human property. However, no previous research has tested this hypothesis in humans using the standard experimental methods applied to non-human species.

The strategic convention model stands in contrast to traditional theories which claim that human property necessarily depends on verbal communication, individual reputation, productive labor, legal institutions, enforcement by authority or other complexities of human social life (Bentham, 1802, Grotius, 1625/1964, Hobbes, 1651, Hume, 1740, Kant, 1797/1991, Locke, 1689, Pufendorf, 1672/2005, Rousseau, 1762). If, instead, basic features of human property can arise from very simple pairwise conflicts, as in species with minimal social interaction, then ownership reflects a core human competency which does not depend on advanced social abilities such as language, reputation or third-party enforcement.

We test whether human fighting decisions are sensitive to resource distribution (uniform or patchy), asymmetries in power and asymmetries in prior possession. We designed custom software to create a virtual environment for observing human resource disputes (see Methods). In each experimental session, 10 participants operate avatars in a virtual environment where they can forage and fight for food items which are convertible to cash (Supplementary Video 1). To secure resources, participants can “strike” other participants, which is costly for both players. Because strikes are implemented through avatars, they cause financial losses but not physical harm (Fig. 1). This allows us to use methods similar to those used in non-human animal studies where animals engage in actual fighting. In the environment, avatars can move to find shrubs, enter/exit shrubs and consume berries inside shrubs. Avatars gain one “health point” for each berry consumed, increasing their health meter (0–100 points) and offsetting health losses from metabolism which occurs at a rate of −10 points per minute. Participants' cash earnings accumulate continuously in proportion to the health of their avatars, providing financial incentives to maximize health. When two avatars enter the same shrub, they have an “interaction” in which each avatar can (1) Leave, allowing the other avatar to consume berries; (2) Smile, which produces a smile; or (3) Strike, which costs the striker one health point and imposes a greater cost (3 or 5 points) on the individual who is struck. Participants remain in the interaction, where they can smile or strike repeatedly, until one avatar leaves the shrub. Finally, we designed an experimenter's monitor (not observed by participants) showing the movements and interactions of all 10 participants in the environment in real time and allowing experimental sessions to be replayed from complete records of participants' actions (Video 2, Video 1).

We tested the hypothesis that resource distribution affects fighting behavior (defendability theory; Brown, 1964) by manipulating whether resources were distributed uniformly or clustered in patches, holding quantity constant. In the patchy condition, 10 brown shrubs produced five berries per minute and five green shrubs produced 20 berries per minute (total=150 berries per minute). In the uniform condition, 30 brown shrubs produced five berries per minute (total=150 berries per minute). We also tested whether participants could resolve resource disputes by using asymmetries in power (created by the experimenter) or asymmetries in prior residence. We manipulated power by randomly assigning half of participants to be Small avatars, whose strikes cause three health points of damage, and the other half to be Large avatars, whose strikes cause five health points of damage. The Large avatars appeared noticeably larger on the screen than the Small avatars (Fig. 1).