As the author correctly points out and the evidence indicates, ownership cannot be fully accounted for by absorbing social norms. This target article makes considerable progress in solving this problem by advocating a computational model primarily based on the interaction of two sets of cognitive systems, competitive acquisition and cooperation interaction.

While the model may explain many ownership examples, not all possessions are fungible commodities to compete and cooperate over but rather can be components of identity as proposed by “the extended self” hypothesis (Hood, Reference Hood2019). Variations of the extended self hypothesis can be found in the writings of William James (Reference James1890), Jean Paul Sartre (Reference Sartre1943) and more recently Russell Belk (Reference Belk1988), to capture the way that the concept of personal identity includes what we own. These may be desirable possessions to compete and cooperate over and hence raise status, but they can also be items, ideas or other owned things that are of relative significant value only to the owners. Owned items can represent part of one's identity and hence, trigger different intuitions and mechanisms not captured in the computational model. How else can we explain the need for ownership and value that individuals place on otherwise worthless sentimental objects, sacred artefacts or memorabilia? Not only are these items of significant value to the owner but that significance is conferred by virtue of unique identity (Hood & Bloom, Reference Hood and Bloom2008) and in the case of memorabilia, physical contact with the previous owner (Newman, Diesendruck, & Bloom, Reference Newman, Diesendruck and Bloom2011). Individual essentialism or haecceity to be more specific (Hood, Reference Hood2014) explains why such items are non-fungible and indeed why some even induce magical contagion beliefs related to essences (Hood, Reference Hood2009).

Another example beyond sentimental items is the ubiquitous endowment effect (Kahneman, Knetsch, & Thaler, Reference Kahneman, Knetsch and Thaler1991). Simply stated, once an item is owned, its value to the owner is increased. This has been explained by prospect theory (Kahneman & Tversky, Reference Kahneman and Tversky1979) but there are aspects of the endowment effect which indicate that an individual's self-concept plays a role. For example, Maddux et al. demonstrated by manipulating the self-construct of individuals who identified with both the individualistic Western culture and the interdependent Eastern culture would moderate the endowment effect as their self construct changed (Maddux et al., Reference Maddux2010). In the traditional Hazda Bushmen of Northern Tanzania where ownership is more collective, the endowment effect has been reported absent in those who do not have experience of trading with others outside of the tribe (Apicella, Azevedo, Christakis, & Fowler, Reference Apicella, Azevedo, Christakis and Fowler2013).

Normally, the endowment effect is not observed in Western children until they are around 5–6-year old (Harbaugh, Krause, & Vesterlund, Reference Harbaugh, Krause and Vesterlund2001), but it can be induced in younger 3–4-year-old children using a paradigm to manipulate their self-concept (Hood, Weltzien, Marsh, & Kanngiesser, Reference Hood, Weltzien, Marsh and Kanngiesser2016). Children were asked to compare toys and give a preference value to each. Identical toys that were given an equal preference value were then distributed to the child and the experimenter. Children were then divided into groups that either constructed a picture of themselves and talked about themselves, made a picture of their best friend and talked about them or a farm-yard scene and asked to describe it. Children were then asked to rate the identical toys again. The group that had been primed to think and talk about themselves showed an endowment effect that was absent in the other groups supporting the notion that possessions are an extension of the self concept when this notion is primed. The development of the ownership concept is linked to the emerging self concept and how that is shaped by culture. This may also explain why individuals with autism lack an endowment effect as their self concept differs from typically developing children (Hartley & Fisher, Reference Hartley and Fisher2017).

Arguably, self-related possessions represent a separate category of ownership. It is likely to have emerged subsequently to mechanisms of competition and cooperation addressed by the computational model, but this category of ownership is one that individuals and groups will fight vigorously over. How else can we explain why territory that is otherwise worthless or strategic can become the focus of conflict because it represents core identity for the groups involved? One could fit this conflict and competition within the computational model suggested but much harder are the sentimental and non-fungible items that are only of significant value to the individual.