294 M. Hoffman et al. Karpoff’s survey, another dictate of participants’ (and the judges’) property rights intuitions was who owned the land on which the lost item was found. Also like animals, our sense of property rights is influenced by who created or invested in the resource, another uncorrelated asymmetry. In locales that sometimes grant property rights to squatters—individuals who occupy lands others have pur- chased—a key determinant of whether the squatters are granted the land is whether they have invested in it (Cone vs. West Virginia Pulp & Paper Co., 1947; Neuwirth, 2005). Locke also intuited that investment in land is part of what makes it ours: In Second Treatise on Civil Government (1689), Locke wrote, “everyman has a property in his person; this nobody has a right to but himself. The labor of his body and the work of his hand, we may say, are properly his.” If the Hawk—Dove model underlies our sense of property rights, we would expect to see psychological mechanisms that motivate us to feel entitled to an object when we possess it or have invested in it. Here are three such mechanisms, which can be seen by reinterpreting some well-documented “biases” in the behavioral economics literature. The first such bias is the endowment effect: We value items more if we are in possession of them. The endowment effect has been documented in dozens of experiments, where subjects are randomly given an item (mug, pen, etc.) and subsequently state that they are willing to sell the mug for much more than those who were not given the mug are willing to pay (Kahneman, Knetsch, & Thaler, 1990). In the behavioral economics literature, the endowment effect has sometimes been explained by loss aversion, which is when we are harmed more by a loss than we benefit from an equivalent gain. However, the source of loss aversion is not questioned or explained. When it is, loss aversion is also readily explained by the Hawk—Dove game (Gintis, 2007). A second bias that also fits