Primary issues raised by the commentaries on the target article relate to (1) the need to differentiate distinct but overlapping aspects of fluid cognition, and (2) the implications that this differentiation may hold for conceptions of general intelligence. In response, I outline several issues facing researchers concerned with differentiation of human cognitive abilities and suggest that a revised and expanded theory of intelligence is needed to accommodate an increasingly diverse and varied empirical base.

Why are people interested in money? Specifically, what could be the biological basis for the extraordinary incentive and reinforcing power of money, which seems to be unique to the human species? We identify two ways in which a commodity which is of no biological significance in itself can become a strong motivator. The first is if it is used as a tool, and by a metaphorical extension this is often applied to money: it is used instrumentally, in order to obtain biologically relevant incentives. Second, substances can be strong motivators because they imitate the action of natural incentives but do not produce the fitness gains for which those incentives are instinctively sought. The classic examples of this process are psychoactive drugs, but we argue that the drug concept can also be extended metaphorically to provide an account of money motivation. From a review of theoretical and empirical literature about money, we conclude that (i) there are a number of phenomena that cannot be accounted for by a pure Tool Theory of money motivation; (ii) supplementing Tool Theory with a Drug Theory enables the anomalous phenomena to be explained; and (iii) the human instincts that, according to a Drug Theory, money parasitizes include trading (derived from reciprocal altruism) and object play.

Why are people interested in money? This question is too broad: there are many kinds of money, interest, and people. The biological approach of Lea & Webley (L&W) makes them seek the roots of this interest, and they contend that tool making and addiction qualify as the roots. Curiosity and the quest for power, however, qualify too. As L&W rightly admit, other approaches supplement their biological one.

An emotional value for money is clearly demonstrable beyond its value for getting goods, but this value need not be ascribed to human preparedness for altruism or play. Emotion is a motivated process, and our temptation to “overgraze” positive emotions selects for emotional patterns that are paced by adequately rare occasions. As a much-competed-for tool, money makes an excellent occasion for emotional reward – a prize with value beyond its tool value – but this is true also of the other facts by which we pace our emotions.

As prototypical incentive with biological meaning, food illustrates the distinction between money as tool and money as drug. However, consistent neuroscience results challenge this view of food as intrinsic value and opposite to drugs of abuse. The scarce availability over evolutionary time of both food and money may explain their similar drug-like non-satiability, suggesting an integrated mechanism for generalized reinforcers.

Social behaviour is but an expression of instinctive mechanisms whereby the aggressive instinct is of particular importance, having given rise to most of the complexity of social behaviour through processes of phylogenetic and cultural ritualisation. The role of the aggressive instinct is to dynamically maintain the ranking order in a group, and much of social interaction is concerned with this, including monetary exchange.

What is certain, is that with the elimination of aggression, … the tackling of a task or problem, the self-respect [in] everything that a man does from morning till evening, from the morning shave to the sublimest artistic or scientific creation, would lose all impetus; everything associated with ambition, ranking order, and countless other equally indispensable behaviour patterns would probably also disappear from human life.

— Konrad Lorenz (1963/2002, p. 269)

Although theorizing the non-tool motivations for desiring money is a worthwhile goal, Lea & Webley (L&W) offer a view that is too individualistic, too biological, and ultimately too linked to a tool-based view of money motivation. I argue that our fascination with money is social, learned, and ritualistic. Through the magic of money rituals we overcome biological motivations and become civilized.

Money does not stimulate receptors in mimicry of natural agonists; so, by definition, money is not a drug. Attractions of money other than to purchase goods and services could arise from instincts similar to hoarding in other species. Instinctual activities without evolutionary function include earning a billion and writing for BBS.

The target article authors have been drawn into two metaphoric models of attitudes toward money that have prevented them from developing a convincing evolutionary theory able to account for the various behaviors they list and categorize as either tool-type or drug-type. Instead, hoarding could provide an evolutionary model that is better supported by behavioral and neurological evidence and could account for the whole range of behaviors they review. Moreover, the authors' focus on money as the common denominator of these behaviors brings an ideological bias to their inquiry.

The metaphor drug model of money slights the possibility that money may literally tap into and exploit brain systems underlying motivational systems, and it also ignores growing evidence on the common neural substrates of behavioral and “physiological” addictions. Additionally, many objects other than money can gain such drug-like properties. The treatment of play in the evolutionary explanation for the unique role of money in people ignores key conceptual and empirical issues.

A testable model of the origin of money is outlined. Based on the notion of epistemic structures, the account integrates the tool and drug views using a common underlying model, and addresses the two puzzles presented by Lea & Webley (L&W) – money's biological roots and the adaptive significance of our tendency to acquire money.

Applying the reciprocity instinct to monetary transactions implies that the reaction to monetary debt and monetary credit are similar. However, evidence suggests an asymmetry. I suggest that the “autonomy instinct” fits better with human behavior towards money. I show that people value autonomy, and I show how money can serve this instinct.

The target article overestimates the power of money as a motive/incentive in order to justify trying to provide a biological theory. A great deal of the article is spent trying to force-fit other explanations into this course categorization. Lea & Webley's (L&W's) account seems to ignore systematic, individual differences, as well as the literature on many negative affective associations of money and behavioural economics, which is a cognitive account of money motivation.

There is “something more” to money, as this incisive review shows. The target article's shortcoming is its overextension of the “drug” metaphor as a blend of features that do not fit the rationalistic economics and behavioral psychologies summarized as tool theories, but this may be resolved by viewing money as a particular case of the more general evolutionary phenomenon of emergent subsystem autonomy.

The biological basis of money lies in a three-term relationship between one subject and some others, with money acting as a mediator. The drive to acquire money is a special case of a desire for recognition. What is aimed at by subjects is their desire for the desire of some others: the former derive satisfaction from representing to themselves the admiration, or envy, of these others. This raises reproductive advantage.

We make two major comments. First, negative reinforcement contingencies may generate some apparent “drug-like” aspects of money motivation, and the operant account, properly construed, is both a tool and drug theory. Second, according to Lea & Webley (L&W), one might expect that “near-money,” such as frequent-flyer miles, should have a stronger drug and a weaker tool aspect than regular money. Available evidence agrees with this prediction.

Currencies that are recognized as money cannot be easily distinguished from alternative currencies such as status. Numerous examples demonstrate the need for status to be recognized as a motivator alongside, at least, money. Lea & Webley (L&W) acknowledge the roles of status; however, a closer focus is warranted.

I focus on the problem of whether a specific biologic basis exists for reinforcing the power of money. I argue in favor of its existence based on a new interpretation of data obtained in experiments with pigeons and rats in an experimental chamber. The experiments demonstrated that in the animals' behavior we can observe some features that had been considered pertinent to human beings only, such as making certain sources of utility “sacred.”

Different aspects of people's interactions with money are best conceptualized using the drug and tool theories. The key question is when these models of money are most likely to guide behavior. We suggest that the Drug Theory characterizes motivationally active uses of money and that the Tool Theory characterizes behavior in motivationally cool situations.

Money is a specifically human incentive. However, functional imaging techniques bring striking evidence that neural circuits pertaining to more “natural” addictive and rewarding processes are involved in response to monetary reward. Main results are evoked here, with specific brain responses demonstrated along the different stages of the process.