Edward H. Hagen

Music and dance as a coalition signaling system

Evidence suggests that humans might have neurological specializations for music processing, but a compelling adaptationist account of music and dance is lacking. The sexual selection hypothesis cannot easily account for the widespread performance of music and dance in groups (especially synchronized performances), and the social bonding hypothesis has severe theoretical difficulties. Humans are unique among the primates in their ability to form cooperative alliances between groups in the absence of consanguineal ties. We propose that this unique form of social organization is predicated on music and dance. Music and dance may have evolved as a coalition signaling system that could, among other things, credibly communicate coalition quality, thus permitting meaningful cooperative relationships between groups. This capability may have evolved from coordinated territorial defense signals that are common in many social species, including chimpanzees. We present a study in which manipulation of music synchrony significantly altered subjects’ perceptions of music quality, and in which subjects’ perceptions of music quality were correlated with their perceptions of coalition quality, supporting our hypothesis. Our hypothesis also has implications for the evolution of psychological mechanisms underlying cultural production in other domains such as food preparation, clothing and body decoration, storytelling and ritual, and tools and other artifacts.

The Functions of Postpartum Depression

Abstract Evolutionary approaches to parental care suggest that parents will not automatically invest in all offspring, and they should reduce or eliminate investment in their children if the costs outweigh the benefits. Lack of paternal or social support will increase the costs born by mothers, whereas infant health problems will reduce the evolutionary benefits to be gained. Numerous studies support the correlation between postpartum depression (PPD) and lack of social support or indicators of possible infant health and development problems. PPD may be an adaptation that informs mothers that they are suffering or have suffered a fitness cost, which motivates them to reduce or eliminate investment in offspring under certain circumstances, and that may help them negotiate greater levels of investment from others. PPD also appears to be a good model for depression in general.

Depression as bargaining: The case postpartum

Abstract It was recently hypothesized that depression might function, in part, as a bargaining strategy when cooperation imposes a net cost, but there are social constraints on defection [Evol. Hum. Behav. 20 (1999) 325.]. If so, such social constraints should be associated with depression, and depression in one partner should be associated with increased investment by other partners. Several predictions of this hypothesis were tested using postpartum depression (PPD) as a model for depression in general. The depression levels, abortion attitudes, additional mating opportunities, and investment in childrearing of 240 mothers and fathers with a new child were measured using self-report instruments. Mothers were also asked whether the new child was planned and whether it was wanted. Perceived constraints on abortion correlated significantly with PPD levels, but, as predicted, only for mothers with an unplanned or unwanted child. Contrary to predictions, perceived constraints imposed by family and friends did not correlate with PPD levels. Sexual opportunities correlated significantly with PPD levels, but, as predicted, only for men. As predicted, PPD levels in one spouse correlated significantly with increased investment in childrearing as reported by the other spouse. PPD levels correlated positively with parity for older women with few future reproductive opportunities, as predicted.

Psychological adaptations for assessing gossip veracity

Evolutionary models of human cooperation are increasingly emphasizing the role of reputation and the requisite truthful “gossiping” about reputation-relevant behavior. If resources were allocated among individuals according to their reputations, competition for resources via competition for “good” reputations would have created incentives for exaggerated or deceptive gossip about oneself and one’s competitors in ancestral societies. Correspondingly, humans should have psychological adaptations to assess gossip veracity. Using social psychological methods, we explored cues of gossip veracity in four experiments. We found that simple reiteration increased gossip veracity, but only for those who found the gossip relatively uninteresting. Multiple sources of gossip increased its veracity, as did the independence of those sources. Information that suggested alternative, benign interpretations of gossip decreased its veracity. Competition between a gossiper and her target decreased gossip veracity. These results provide preliminary evidence for psychological adaptations for assessing gossip veracity, mechanisms that might be used to assess veracity in other domains involving social exchange of information.

Revealing the paradox of drug reward in human evolution

Neurobiological models of drug abuse propose that drug use is initiated and maintained by rewarding feedback mechanisms. However, the most commonly used drugs are plant neurotoxins that evolved to punish, not reward, consumption by animal herbivores. Reward models therefore implicitly assume an evolutionary mismatch between recent drug-profligate environments and a relatively drug-free past in which a reward centre, incidentally vulnerable to neurotoxins, could evolve. By contrast, emerging insights from plant evolutionary ecology and the genetics of hepatic enzymes, particularly cytochrome P450, indicate that animal and hominid taxa have been exposed to plant toxins throughout their evolution. Specifically, evidence of conserved function, stabilizing selection, and population-specific selection of human cytochrome P450 genes indicate recent evolutionary exposure to plant toxins, including those that affect animal nervous systems. Thus, the human propensity to seek out and consume plant neurotoxins is a paradox with far-reaching implications for current drug-reward theory. We sketch some potential resolutions of the paradox, including the possibility that humans may have evolved to counter-exploit plant neurotoxins. Resolving the paradox of drug reward will require a synthesis of ecological and neurobiological perspectives of drug seeking and use.

Evolutionary theories of depression: a critical review.

We critically review evolutionary theories of major depressive disorder (MDD). Because most instances of MDD appear to be caused by adversity, evolutionary theories of MDD generally propose that sadness and low mood evolved as beneficial responses to adversity, and that MDD is dysfunctional sadness and low mood. If so, MDD research should focus much more heavily on understanding the healthy functions of sadness and low mood to better understand how they dysfunction. A debate about the boundary between healthy sadness and MDD is then reviewed. In part, this debate turns on whether MDDs costliest symptoms could provide unknown benefits. Therefore, the review concludes by discussing 2 theories that explore possible benefits of prolonged anhedonia and suicidality.

ECOLOGY AND NEUROBIOLOGY OF TOXIN AVOIDANCE AND THE PARADOX OF DRUG REWARD

Current neurobiological theory of drug use is based on the observation that all addictive drugs induce changes in activity of dopaminergic circuitry, interfering with reward processing, and thus enhancing drug seeking and consumption behaviors. Current theory of drug origins, in contrast, views almost all major drugs of abuse, including nicotine, cocaine and opiates, as plant neurotoxins that evolved to punish and deter herbivores. According to this latter view, plants should not have evolved compounds that reward or reinforce plant consumption. Mammals, in turn, should not have evolved reinforcement mechanisms easily triggered by toxic substances. Situated in an ecological context, therefore, drug reward is a paradox. In an attempt to resolve the paradox, we review the neurobiology of aversive learning and toxin avoidance and their relationships to appetitive learning. We seek to answer the question: why does aversive learning not prevent the repeated use of plant drugs? We conclude by proposing alternative models of drug seeking and use. Specifically, we suggest that humans, like other animals, might have evolved to counter-exploit plant neurotoxins.

Did Neanderthals and other early humans sing? Seeking the biological roots of music in the territorial advertisements of primates, lions, hyenas, and wolves

Group defence of territories is found in many gregarious mammalian carnivores, including lions, canids, and hyenas. In these taxa, group members often mark territory boundaries and direct aggressive behaviour towards alien conspecifics found within the territory (Boydston et al., 2001). Middle Pleistocene hominids such as Neanderthals occupied an ecological niche similar to such large carnivores (Stiner, 2002), and so could be expected to share with them a suite of behavioural traits. Complex, coordinated vocalizations that function, at least in part, to advertise the group defence of a territory is one behavioural trait exhibited by several social carnivores, as well as many other gregarious animals, including primates. Hagen and Bryant (2003) proposed that the evolution of human music and dance was rooted in such coordinated auditory and visual territorial advertisements, an hypothesis we develop and expand upon here. Human proto-music, in essence, might have been functionally analogous to the howling of wolves.

Explaining Human Recreational Use of ‘pesticides’: The Neurotoxin Regulation Model of Substance Use vs. the Hijack Model and Implications for Age and Sex Differences in Drug Consumption

Most globally popular drugs are plant neurotoxins or their close chemical analogs. These compounds evolved to deter, not reward or reinforce, consumption. Moreover, they reliably activate virtually all toxin defense mechanisms, and are thus correctly identified by human neurophysiology as toxins. Acute drug toxicity must therefore play a more central role in drug use theory. We accordingly challenge the popular idea that the rewarding and reinforcing properties of drugs “hijack” the brain, and propose instead that the brain evolved to carefully regulate neurotoxin consumption to minimize fitness costs and maximize fitness benefits. This perspective provides a compelling explanation for the dramatic changes in substance use that occur during the transition from childhood to adulthood, and for pervasive sex differences in substance use: because nicotine and many other plant neurotoxins are teratogenic, children, and to a lesser extent women of childbearing age, evolved to avoid ingesting them. However, during the course of human evolution many adolescents and adults reaped net benefits from regulated intake of plant neurotoxins.

Living with Kin in Lowland Horticultural Societies

Postmarital residence patterns in traditional human societies figure prominently in models of hominid social evolution with arguments for patrilocal human bands similar in structure to female-dispersal systems in other African apes. However, considerable flexibility in hunter-gatherer cultures has led to their characterization as primarily multilocal. Horticulturalists are associated with larger, more sedentary social groups with more political inequality and intergroup conflict and may therefore provide additional insights into evolved human social structures. We analyze coresidence patterns of primary kin for 34 New World horticultural societies (6,833 adults living in 243 residential groupings) to show more uxorilocality (women live with more kin) than found for hunter-gatherers. Our findings further point to the uniqueness of human social structures and to considerable variation that is not fully described by traditional postmarital residence typologies. Sex biases in coresident kin can vary according to the scale of analysis (household vs. house cluster vs. village) and change across the life span, with women often living with more kin later in life. Headmen in large villages live with more close kin, primarily siblings, than do nonheadmen. Importantly, human marriage exchange and residence patterns create meta-group social structures, with alliances extending across multiple villages often united in competition against other large alliances at scales unparalleled by other species.