Anna Machin

The brain opioid theory of social attachment: a review of the evidence

The psychology of close human relationships is increasingly well understood and our understanding of the neurobiology of the onset of pairbonding behaviour in a range of species has benefited from the use of rodent-based models. However, the human literature has suffered from a lack of focus upon the unique nature of primate social bonds and has so far failed to adequately identify the neurobiological and behavioural mechanisms which maintain these complex, diverse and enduring social networks. One neurobiological mechanism that has been overlooked is the endogenous opioid system. Though less explicitly researched than the more familiar oxytocin/vasopressin system, there is considerable evidence that the opioids play a fundamental role in sociality, especially in the primates. This review summarises our current understanding of the evidence for the role of this system in prosocial behaviour in non-primate mammals, nonhuman primates and humans. An important conclusion is that the opioid system may play a more central role in sociality in primates (including humans) than in other mammalian taxa.

Social touch modulates endogenous μ-opioid system activity in humans

In non-human primates, opioid-receptor blockade increases social grooming, and the endogenous opioid system has therefore been hypothesized to support maintenance of long-term relationships in humans as well. Here we tested whether social touch modulates opioidergic activation in humans using in vivo positron emission tomography (PET). Eighteen male participants underwent two PET scans with [11C]carfentanil, a ligand specific to μ-opioid receptors (MOR). During the social touch scan, the participants lay in the scanner while their partners caressed their bodies in a non-sexual fashion. In the baseline scan, participants lay alone in the scanner. Social touch triggered pleasurable sensations and increased MOR availability in the thalamus, striatum, and frontal, cingulate, and insular cortices. Modulation of activity of the opioid system by social touching might provide a neurochemical mechanism reinforcing social bonds between humans.

The role of the individual agent in Acheulean biface variability: A multi-factorial model

The Lower Palaeolithic, epitomized by the Acheulean biface technology, is characterized by a degree of temporal and geographical stasis that is unparalleled in the lithic record. The reasons for this phenomenon have provoked considerable debate. However, whilst it is important to understand the overall stability of this techno complex, it is also important to address the considerable degree of variability evident at the level of individual locales. Why, for instance, do bifaces show a range of shapes and degrees of refinement? Why do some show high degrees of symmetry whilst others do not? Whilst it is widely acknowledged that such variability is the result of a number of factors, to date proposed theories tend to stress one factor as being of paramount importance. These have encompassed, amongst others, the influence of raw material, subsistence function, cognitive ability and the social context of manufacture upon biface form. This article, informed by recent empirical, experimental and theoretical work, attempts to move away from these largely single-factor models to present a multi-factorial model for biface variability. This model envisages that variability is caused by the differing motivations and constraints — ecological, physiological, biological, cognitive and social — which act upon the individual agent at any given point in time.

Variation in the β-endorphin, oxytocin, and dopamine receptor genes is associated with different dimensions of human sociality

Significance Social behavior in mammals is underpinned by a number of social neuropeptides. Most studies, however, focus on a single neuropeptide (often oxytocin), and invariably only in the context of reproductive relationships. Here, we examine the associations between the six main social neuropeptides (endorphins, oxytocin, vasopressin, dopamine, serotonin, and testosterone) and social indices in three separate social domains (disposition, dyadic/romantic relationships, and social network). We show that each neuropeptide is quite specific in its domain of influence, although endorphins and dopamine influence all three social domains. The results suggest that the social importance of endorphins may have been underestimated. There is growing evidence that the number and quality of social relationships have substantial impacts on health, well-being, and longevity, and, at least in animals, on reproductive fitness. Although it is widely recognized that these outcomes are mediated by a number of neuropeptides, the roles these play remain debated. We suggest that an overemphasis on one neuropeptide (oxytocin), combined with a failure to distinguish between different social domains, has obscured the complexity involved. We use variation in 33 SNPs for the receptor genes for six well-known social neuropeptides in relation to three separate domains of sociality (social disposition, dyadic relationships, and social networks) to show that three neuropeptides (β-endorphin, oxytocin, and dopamine) play particularly important roles, with each being associated predominantly with a different social domain. However, endorphins and dopamine have a much wider compass than oxytocin (whose effects are confined to romantic/reproductive relationships and often do not survive control for other neuropeptides). In contrast, vasopressin, serotonin, and testosterone play only limited roles.

Why handaxes just aren't that sexy: A response to Kohn & Mithen (1999)

The Acheulean handaxe is one of the most iconic, analysed and fiercely debated artefacts from the prehistoric period. Persisting for over one million years and recovered from sites across the Old World its distinctive, often symmetrical, tear drop or ovate shape appears to be over-engineered for a subsistence function alone. Debate has centred upon trying to unravel the reasons for this form; raw material, knapping technique, subsistence function, cognition, social context of manufacture and sexual selection have all been proposed as key factors (Jones 1994; White 1998; Gamble 1999; Kohn & Mithen 1999; McPherron 2000; Gowlett 2006).

Sex differences in relationship conflict and reconciliation

Friendships and other relationships are crucial to human fitness, yet such relationships often terminate acrimoniously. We explore the pattern of relationship conflict, and the processes of reconciliation that are used to repair them. In this sample, an individual fell out with one member of their extended network, on average, every 7.2 months. Conflict with very close family is surprisingly high; nonetheless, most conflicts involve unrelated individuals (friends, colleagues), suggesting that kin relationships are relatively more buffered against the stresses that trigger conflict (reflecting the “kinship premium”). Around 40% of conflicts remain unreconciled after a year. There were striking sex differences in the intimacy of the relationships involved in breakdown, and the precipitating causes, as well as whom participants reported falling out with. These patterns may reflect women’s preference for fewer, more intimate (and correspondingly more fragile) relationships. The functional origins of this gend...

Social Psychology and the Comic-Book Superhero: A Darwinian Approach

Why is the comic-book superhero such a persistent topic of cultural representation? Citing Dutton’s evolutionary aesthetic, we argue that comic-book superheroes persist because they offer a cultural means of negotiating the gap between the small group size that human beings have evolved a cognitive architecture to deal with, and the much larger group size that is entailed by modern social arrangements. This position implies four predictions: the superhero should (1) exhibit punitive prosociality, (2) be supernatural or quasi-supernatural, (3) be minimally counterintuitive, and (4) display kin-signaling proxies. These predictions are tested against seventeen superhero figures from various comic-book universes.