Money is a cultural construction, leukemia is not. In which category does phenomenal consciousness fit? The issue is clarified by a distinction between what cultural phenomena causally influence and what culture constitutes. Culture affects phenomenal consciousness but it is ridiculous to suppose that culture constitutes it, even in part.

Structure entails arrangements and interrelations of parts that organize the whole (i.e., personality). It involves stability of traits over time. Extraversion varies along a continuum towards introversion. Multiple behavioral and biological variables in several systems vary and are regulated homeostatically within the normal range. If there is a fixed point for an individual, what inhibits variation in the biological parameter?

The evolutionary theory of sex implies a theoretically principled account of the causal mechanisms underlying personality systems in which males pursue a relatively high-risk strategy compared to females and are thus higher on traits linked to sensation seeking and social dominance. Females are expected to be lower on these traits but higher on traits related to nurturance and attraction to long-term relationships. The data confirm this pattern of sex differences. It is thus likely that these traits have been a focus of natural selection rather than the traits of gregarious/aloof and arrogant/unassuming hypothesized by Depue & Collins.

In “Lifelines” Steven Rose constructs a case against neurogenetic determinism based on experimental data from biology and in favor of a significant degree of self determination. Two philosophical errors in the case favoring neurogenetic determinism are illustrated by Rose: category mistakes and an excessively narrow view of causality restricted to the linear form.

Data from further human experiments touch four open questions in the target article. (1) Extinction of reward acquisition postulated by Depue & Collins's model could not be confirmed if correlating craving for, liking of, and satisfaction from smoking. (2) Intraindividual correspondence between responsivity to dopamine agonists and antagonists could likewise not be confirmed. (3) Nicotine craving and drug-induced hormone responses were not substantially correlated. (4) Low serotonin can be the cause and not just the moderator of dopaminergic sensitivity, and personality correlates of low dopamine/low MAO (aggressive impulsive traits) can hardly be related to the positive emotion associated with dopaminergic activity.

Although Rose claims to rely on Marx's paradoxical view of history to explain the freedom enjoyed by what he calls “lifelines,” he blurs what one might call the “objective” and “subjective” senses of freedom. This, in turn, reflects his overreaction to biological reductionism. Consequently, in discussing biology-related policy issues, Rose fails to distinguish genuinely efficacious interventions and merely convenient ones.

Rose's accomplishment in combining ontological unity with epistemological diversity contrasts it with Wilson's failure in overemphasizing the former and not appreciating the latter. This commentary cites the two most authoritative discussions of the inapplicability of heritability to human data, corrects several historical errors or inaccuracies in genetics, and criticizes the characterizations of Jacques Loeb and Robert Plomin.

Sensitivity to incentive motivation has a formative influence on extraversion. Mesoamygdaloid dopamine (DA) activity may, at one level, act as a micro-gate permitting an incentive to influence behavioral organization – “Go/No-Go” in this scheme. Data on function elsewhere in the mesocorticolimbic DA system are taken to support this particular function. At another level of analysis, the data in Depue & Collins's review, along with those on the rest of the ventral tegmental area (VTA) system, may fit better with a “switching” function in information processing. This link is supported by correlations between measures of extraversion, learned inattention, and overall DA activity. The point is extended to the novelty-seeking feature of the extraverted personality.

Stephen Rose's formulation of evolutionary theory is too scattered and impressionistic to serve as a genuine alternative to ultra- Darwinism. In addition, he has muddied a distinction that is crucial to our understanding of evolutionary phenomenona – the distinction between homologies and homoplasies.

A major dopaminergic role for extraversion is compromised by the fact that affiliation and impulsivity tend to be reduced by psychostimulants. Also, the large clinical literature on the treatment of ADHD with drugs that promote dopamine activity provides little or no support for a major role for dopamine in human extraversion. Dopamine facilitation of agency may be more evident for inanimate rather than animate rewards.

Rose provides a coherent account of how a number of simplifying assumptions apparently come together to support neurogenetic determinism, or “ultra-Darwinism.” This view, he demonstrates, is deeply flawed. He proposes instead that we must take account of the interaction of processes that determine our developmental trajectory at every stage. Unfortunately, he associates this defensible position with the claim that this gives freedom of action to humans. The implications of this for the interpretation of his general thesis are discussed.

Depue & Collins associate dopaminergically mediated incentive motivational processes with extraversion. In this commentary I consider dopaminergic indices from neuroimaging investigations which correlate more closely with impulsive sensation seeking personality traits than with extraversion. Measures of relevant behavioural processes also appear to correlate with personality measures other than extraversion.

Rose seems to be arguing against an extreme ultra-Darwinism that probably has no adherents. He incorrectly argues that a number of psychological traits are very difficult to measure. This is not the case. Rose argues that intelligence has no biological correlates. In fact, it is correlated with brain size, EEG evoked potentials, and cerebral glucose uptake during problem solving. Data that Rose should be aware of are omitted when they do not fit the case he is trying to make.

Depue & Collins's general idea of a functional relationship between DA activity and extraversion is an important step toward an integrative biological model of personality. However, focusing primarily on incentive motivation and variations in VTA DA activity as basic behavioral and biological components underlying extraversion appears too limited. Existing data suggest that responsivity to changes in DA activity is higher in introverts than in extraverts. This may reflect a general, extraversion- related characteristic of the entire dopaminergic network in the brain.

Lifelines by Steven Rose is supposed to present a new perspective on biology replacing an emphasis on genes with one on organisms. However, much of the book is a highly biased critique of sociobiology and behavior genetics. Some of the flaws in Rose's description and depiction of these fields are presented and refuted. Also, it would appear that these aspects of the book and many others are, in fact, related more to Rose's perennial concern for the ideology, social origins or social consequences of behavioral biology. These concerns are, I believe based, in part, upon Rose's misunderstandings and misinterpretations of genetics, behavior genetics, and sociobiology.

This commentary examines the implications of the Depue & Collins model for the etiology and treatment of depression, specifically, whether it can account for findings concerning neurobiological, behavioral, and phenomenological facets of depression. Drawing upon the construct of self-regulation, I explore the fit of the model to current knowledge about depression, conceptualized as a dysfunction within a hypothetical brain/behavior system for maximizing positive outcomes.

Sex differences in motivation and emotional reactions to casual sex suggest that the links to extraversion, constraint, impulsivity-sensation seeking, and sexual behavior differ for men and women. Because both testosterone and dominance, and dominance and number of sex partners appear to correlate in men but not in women, it is plausible that testosterone is involved in the creation and maintenance of these sex differences in linkage among the behavioral subsystems involved in sexuality and extraversion.

Research pragmatics, not a defective conceptual framework, supports modern biological reductionism. Conducting research to reveal the casual web underlying the multiple developmental pathways leading to any species-specific characteristic requires better research techniques than those commonly used. It takes much patience, time, and effort to gain even small glimpses of an answer to any developmental question.

Depue & Collins propose that extraversion should be separated from the impulsivity-constraint dimension of personality, and that the VTA dopamine system is the primary engine of extraversion. Although their focus is on personality traits, it may be useful to consider the evidence on psychological state changes, related both to affective arousal and to drug effects. This evidence shows that there are inherent relations between extraversion and impulsivity-constraint, and that there are influences of dopamine on impulsivity-constraint that are not consistent with the Depue & Collins model. Increased positive affect leads to increased extraversion, and this is associated with more impulsivity and less constraint. The evidence on drug effects shows that greater dopaminergic control is associated with more constraint, and with anxiety and vigilance rather than positive affect.

Complete determinism is, as Karl Popper said, “a daydream of omniscience.” Determinism is usually conceived as linked with a particular science whose explanations are deemed fundamental. As Rose rightly points out, biological enquiry includes many different kinds of question. Genetic determinism, making genes central to biology, is therefore biased and misguided. The crucial unit must be the whole organism.