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Objective: In a UK national census sample, women from the upper and lower socioeconomic (SES) classes achieve parity in completed family size, despite marked differences in both birth rates and offspring survival rates. We test the hypothesis that women adopt reproductive strategies that manipulate age at first reproduction to achieve this., Methods: We use a Monte-Carlo modeling approach parameterized with current UK lifehistory data to simulate the reproductive lifehistories of 64,000 individuals from different SES classes, with parameter values at each successive time step drawn from a statistical distribution defined by the census data., Results: We show that, if they are to achieve parity with women in the higher socioeconomic classes, women in lower socioeconomic classes must begin reproducing 5.65 years earlier on average than women in the higher SES classes in order to offset the higher class-specific mortality and infertility rates that they experience. The model predicts very closely the observed differences in age at first reproduction in the census data., Conclusions: Opting to delay reproduction in order to purse an education-based professional career may be a high risk strategy that many lower SES women are unwilling and unable to pursue. As a result, reproducing as early as possible may be the best strategy available to them., Competing Interests: Conflict of InterestThe authors declare that they have no conflict of interest., (© The Author(s) 2024.)

Host-associated microbiomes play an increasingly appreciated role in animal metabolism, immunity and health. The microbes in turn depend on their host for resources and can be transmitted across the host's social network. In this Perspective, we describe how animal social interactions and networks may provide channels for microbial transmission. We propose the 'social microbiome' as the microbial metacommunity of an animal social group. We then consider the various social and environmental forces that are likely to influence the social microbiome at multiple scales, including at the individual level, within social groups, between groups, within populations and species, and finally between species. Through our comprehensive discussion of the ways in which sociobiological and ecological factors may affect microbial transmission, we outline new research directions for the field.

Objective: This article addresses the connection between loneliness and physical contact. Evolutionary and psychological research has shown that touch is an important part of bond-building and emotion communication; loneliness is intimately related to these elements as well. In this paper, we ask whether physical contact reduces feelings of loneliness -which might derive from evolutionary ancient bonding mechanisms-despite a cultural context that is relatively non-tactile., Method: An experimental study (40 participants, 13 males) tested for observable effects of touch on loneliness scores in a low-contact culture to analyse whether they respond positively to that stimulus despite cultural training against it., Results: Participants exposed to physical contact reported significantly lower neglect scores from their close relationships in a short loneliness scale, thus suggesting that there is an underlying mechanism that persists despite enculturation. The effects were particularly strong among single people, which could mean that lower loneliness among married people might be partly explained by the regular availability of physical contact. Participants in the experimental condition also showed a faster reduction in heart rate, interpreted as a sign of physiological wellbeing., Conclusions: These findings help to specify mechanisms within the evolutionary theoretical framework of loneliness that link internal feelings to environmental cues. This article aims at contributing to a more complex discussion on the interactions between emotions, cultural practices and psychological well-being., Competing Interests: Conflict of InterestOn behalf of all authors, the corresponding author states that there is no conflict of interest., (© Springer Nature Switzerland AG 2020.)

Objectives: Sociality is underpinned by a variety of neurochemicals. We previously showed, in a large healthy Caucasian sample, that genes for different neurochemicals are typically associated with differing social domains (disposition, romantic relationships and networks). Here we seek to confirm the validity of these findings by asking whether they replicate in other population samples., Methods: We test for associations between the same 24 Single Nucleotide Polymorphisms (SNPs) and measures of sociality as previously, in two smaller independent samples: Caucasian individuals with histories of mental illness (subclinical sample) ( N  = 140), and non-Caucasian individuals ( N  = 66). We also combined the relevant SNPs and social measures into 18 distinct neurochemical/social domain categories to examine the distribution of significant associations across these., Results: In the subclinical Caucasian sample, we confirm previous associations between (i) specific oxytocin and dopamine receptor gene SNPs and sexual attitudes and behavior, and (ii) two SNPs associated with dopamine receptor 2 and feelings of inclusion in the local community. In the non-Caucasian sample, we replicate the previous association between an oxytocin receptor SNP and anxious attachment. More generally, chi-squared tests indicated that the distribution of significant associations for each neurochemical across the three social domains did not differ significantly between the original sample and either of the new samples, except for oxytocin in the non-Caucasian sample., Conclusions: These results corroborate both the SNP-specific and broader neurochemical associations with particular facets of sociality in two new populations, thereby confirming the validity of the previous findings., Competing Interests: Compliance with Ethical StandardsThe authors declare no conflict of interest.

Communal eating, whether in feasts or everyday meals with family or friends, is a human universal, yet it has attracted surprisingly little evolutionary attention. I use data from a UK national stratified survey to test the hypothesis that eating with others provides both social and individual benefits. I show that those who eat socially more often feel happier and are more satisfied with life, are more trusting of others, are more engaged with their local communities, and have more friends they can depend on for support. Evening meals that result in respondents feeling closer to those with whom they eat involve more people, more laughter and reminiscing, as well as alcohol. A path analysis suggests that the causal direction runs from eating together to bondedness rather than the other way around. I suggest that social eating may have evolved as a mechanism for facilitating social bonding., (© The Author(s) 2017.)

Alcohol use has a long and ubiquitous history. Despite considerable research on the misuse of alcohol, no one has ever asked why it might have become universally adopted, although the conventional view assumes that its only benefit is hedonic. In contrast, we suggest that alcohol consumption was adopted because it has social benefits that relate both to health and social bonding. We combine data from a national survey with data from more detailed behavioural and observational studies to show that social drinkers have more friends on whom they can depend for emotional and other support, and feel more engaged with, and trusting of, their local community. Alcohol is known to trigger the endorphin system, and the social consumption of alcohol may thus have the same effect as the many other social activities such as laughter, singing and dancing that we use as a means of servicing and reinforcing social bonds., (© The Author(s) 2016.)