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Why humans cooperate in large groups and with non-kin remains a puzzle for researchers across the natural and social sciences. Investigating whether cooperation is sexually selected could contribute to an understanding of the evolution of human cooperation. Competition for access to mates could indeed select for cooperation. Using controlled laboratory experiments, we analyse whether and how the sex composition of a social environment, testosterone level, and relationship status affect contributions to a public good. The results show that variation in sex composition alters the amount of money that single men (but not men in a couple or women) contribute to a public good. Notably, in line with the competitive helping hypothesis, awareness of the presence of a woman leads to larger contributions by single men, most likely by triggering their competitiveness to be the most cooperative man in the group. However, we find no link between basal testosterone level and cooperativeness. We argue that men, notably single men, adopt cooperative behaviours as a signalling strategy in the context of mate choice and hence that cooperation is partly sexually selected. Our findings highlight the need to consider sexual selection as an additional mechanism for cooperation.
If attractiveness is an important cue for mate choice, as proposed by evolutionary psychologists, then attractive individuals should have greater mating success than their peers. We tested this hypothesis in a large sample of adults. Facial attractiveness correlated with the number of short-term, but not long-term, sexual partners, for males, and with the number of long-term, but not short-term, sexual partners and age of first sex, for females. Body attractiveness also correlated significantly with the number of short-term, but not long-term, sexual partners, for males, and attractive males became sexually active earlier than their peers. Body attractiveness did not correlate with any sexual behavior variable for females. To determine which aspects of attractiveness were important, we examined associations between sexual behaviors and three components of attractiveness: sexual dimorphism, averageness, and symmetry. Sexual dimorphism showed the clearest associations with sexual behaviors. Masculine males (bodies, similar trend for faces) had more short-term sexual partners, and feminine females (faces) had more long-term sexual partners than their peers. Feminine females (faces) also became sexually active earlier than their peers. Average males (faces and bodies) had more short-term sexual partners and more extra-pair copulations (EPC) than their peers. Symmetric women (faces) became sexually active earlier than their peers. Given that male reproductive success depends more on short-term mating opportunities than does female reproductive success, these findings suggest that individuals of high phenotypic quality have higher mating success than their lower quality counterparts.
Researchers from multiple fields have sought to understand how sex moderates human social behavior. While over 50 years of research has revealed differences in cooperation behavior of males and females, the underlying neural correlates of these sex differences have not been explained. A missing and fundamental element of this puzzle is an understanding of how the sex composition of an interacting dyad influences the brain and behavior during cooperation. Using fNIRS-based hyperscanning in 111 same- and mixed-sex dyads, we identified significant behavioral and neural sex-related differences in association with a computer-based cooperation task. Dyads containing at least one male demonstrated significantly higher behavioral performance than female/female dyads. Individual males and females showed significant activation in the right frontopolar and right inferior prefrontal cortices, although this activation was greater in females compared to males. Female/female dyad’s exhibited significant inter-brain coherence within the right temporal cortex, while significant coherence in male/male dyads occurred in the right inferior prefrontal cortex. Significant coherence was not observed in mixed-sex dyads. Finally, for same-sex dyads only, task-related inter-brain coherence was positively correlated with cooperation task performance. Our results highlight multiple important and previously undetected influences of sex on concurrent neural and behavioral signatures of cooperation.
Humans regularly cooperate with non-kin, which has been theorized to require reciprocity between repeatedly interacting and trusting individuals. However, the role of repeated interactions has not previously been demonstrated in explaining real-world patterns of hunter–gatherer cooperation. Here we explore cooperation among the Agta, a population of Filipino hunter–gatherers, using data from both actual resource transfers and two experimental games across multiple camps. Patterns of cooperation vary greatly between camps and depend on socio-ecological context. Stable camps (with fewer changes in membership over time) were associated with greater reciprocal sharing, indicating that an increased likelihood of future interactions facilitates reciprocity. This is the first study reporting an association between reciprocal cooperation and hunter–gatherer band stability. Under conditions of low camp stability individuals still acquire resources from others, but do so via demand sharing (taking from others), rather than based on reciprocal considerations. Hunter–gatherer cooperation may either be characterized as reciprocity or demand sharing depending on socio-ecological conditions.
Grief can be an awful thing. The loss of someone or something can dominate our lives for months, if not years, after the event. Surely – from an evolutionary perspective – such behaviour can’t be beneficial. All the “wasted” time, effort and resources is hardly likely to improve our survival odds; and that’s not even counting the physical and mental harm that can stem from it. It must just be an unfortunate side effect of our emotional investment in people, pets and things (an emotional investment which is likely beneficial). However, a team of psychologists from Florida disagrees1. They’ve published research revealing that grief may have given our species an evolutionary advantage after all.
Their idea stems from the evolutionary phenomena of “costly signalling”. This is when an animal deliberately screws itself over; showing how great it must be to survive despite that disadvantage. The classic example of this is male peacocks, whose huge tails can hinder their movement and flight. If they can survive despite this (in fact, flourish despite this. The energy needed to sustain that tail isn’t insignificant) surely they have great genes and all the peahens should totally mate with them1.
Chimpanzee grief? An adult stands over a recently deceased child
Nature is full of examples of animals that have evolved a disadvantage to “show off”; increasing their evolutionary success in the long run. In this new study, the psychologists argue that grief may be a similar sort of emotional costly signal. If someone gets really upset when a relationship ends then clearly they invest a lot in their relationships; making them an excellent choice for a mate. Effectively, grief evolved as a sort of emotional peacocks tail; showing off just how much we care1.
Which is a nice idea, but is it right? If it was, one might expect people to have a higher opinion of those who exhibited more grief (as their peacock tail was more impressive). So the psychologists conducted a series of experiments to test this prediction; getting participants to read stories about people who had lost loved ones1.
They varied the severity of grief they expressed to see if it resulted in variation of how much people liked them. This ranged from simply describing “John’s wife died” to “John’s wife died and he grieved for 3 years” (with variation in between). They also varied it between third and first person (e.g. “my wife died”) to see if that had an effect. Finally, they got the participants to pick one of these people to be a partner in a trust game; seeing if the varying levels of grief influenced their decision1.
In every case the person who grieved more was viewed as a better person. They were ranked as more trustworthy, a more desirable friend, a nicer person, more loyal and having a greater capacity for forming emotional bonds. In short, grief did seem to act as a signal that the griever forms stronger relationships; making them a more desirable person to form said relationships with1.
Cuteness in offspring is a potent protective mechanism that ensures survival for otherwise completely dependent infants. Previous research has linked cuteness to early ethological ideas of a ‘Kindchenschema’ (infant schema) where infant facial features serve as ‘innate releasing mechanisms’ for instinctual caregiving behaviours. We propose extending the concept of cuteness beyond visual features to include positive infant sounds and smells. Evidence from behavioural and neuroimaging studies links this extended concept of cuteness to simple ‘instinctual’ behaviours and to caregiving, protection, and complex emotions. We review how cuteness supports key parental capacities by igniting fast privileged neural activity followed by slower processing in large brain networks also involved in play, empathy, and perhaps even higher-order moral emotions.
The parent–infant relation is fundamental to infant survival and development.
Cuteness has emerged as an important factor for attracting caregiver attention and affection.
Cuteness is not limited to visual infant features, but is also found in positive sounds and smells.
Neuroimaging has started to identify how survival-related infant-positive and negative stimuli elicit core affective brain activity through fast attentional biasing and slow appraisal processes.
Beyond caregiving, cuteness has a key role in facilitating social relations, pleasure, and well-being, as well as increasing empathy and compassion.