If Tool Theory is buttressed by fundamental concepts of conditioned reinforcement and extinction, a dependence on Drug Theory may not be necessary.

Lea & Webley's (L&W's) non-exclusive distinction between tool-like and drug-like motivators is insufficiently discriminating to say much about money that is useful, as the distinction's equivocal application to sex, food, and drugs shows. Further, it appears as though the motivations of problem gamblers are non-metaphorically like those of drug addicts.

The problem of the biology of money is twofold: It subsumes both the identification of behavioral mechanisms that account for the power of money as an incentive, and the elucidation of the phylogeny of such mechanisms. The drugs–tool distinction, as articulated by Lea & Webley (L&W) in their fascinating synthesis, is a welcome step toward their solution. Compared to the direct invocation of instinctual drives, however, conditioning processes provide a conceptually and empirically clearer road from evolution to money.

Lea & Webley's (L&W's) Drug Theory solves many puzzles surrounding money-related behavior. I explore supplementing the Drug Theory with ideas from gene-culture coevolution theory and memetic theory.

Lea & Webley (L&W) provide two alternative biological accounts of human monetary motivations, the Tool Theory and the Drug Theory. They argue that both are required for an adequate explanation. I explore the applicability of these models to philosophical discussions of how we might justify such motivations. I argue their approach is not entirely satisfactory for normative questions, since it precludes the possibility of rational non-instrumental attitudes towards money.

Our response amplifies our case that money is best seen as both a drug and a tool. Some commentators challenge our core assumptions: In this response we, therefore, explain in more detail why we assume that money is an exceptionally strong motivator, and that a biological explanation of money motivation is required. We also provide evidence to support those assumptions. Other commentators criticise our use of the drug metaphor, particularly arguing that it is empirically empty; and in our response we seek to show how it can be submitted to test – aided by some commentaries which suggest such tests. In addition, we explain, with evidence, why we do not think that the notion of money as a generalised conditioned reinforcer provides a satisfactory alternative to the tool/drug account. The largest group of commentaries suggests alternative instincts on which the drug-like effects of money might be based, other than the reciprocation and play instincts we propose; in our response, we explain why we still prefer our original proposals, but we accept that alternative or additional instincts may indeed underlie money motivation. A final group of commentaries carries the argument further, suggesting extensions to the tool/drug model, in ways with which we are broadly in sympathy. The purpose of the tool and drug metaphors is to encourage reflection on the biological origins of money motivation, and to that extent at least we believe that they have succeeded.