Sunday, October 21, 2018

Our findings challenge the notion of pervasive biases towards female‐biased infection immunity and the role of testosterone in driving these differences

Sexual dimorphism in immunity across animals: a meta‐analysis. Clint D. Kelly et al. Ecology Letters.

Abstract: In animals, sex differences in immunity are proposed to shape variation in infection prevalence and intensity among individuals in a population, with females typically expected to exhibit superior immunity due to life‐history trade‐offs. We performed a systematic meta‐analysis to investigate the magnitude and direction of sex differences in immunity and to identify factors that shape sex‐biased immunocompetence. In addition to considering taxonomic and methodological effects as moderators, we assessed age‐related effects, which are predicted to occur if sex differences in immunity are due to sex‐specific resource allocation trade‐offs with reproduction. In a meta‐analysis of 584 effects from 124 studies, we found that females exhibit a significantly stronger immune response than do males, but the effect size is relatively small, and became non‐significant after controlling for phylogeny. Female‐biased immunity was more pronounced in adult than immature animals. More recently published studies did not report significantly smaller effect sizes. Among taxonomic and methodological subsets of the data, some of the largest effect sizes were in insects, further supporting previous suggestions that testosterone is not the only potential driver of sex differences in immunity. Our findings challenge the notion of pervasive biases towards female‐biased immunity and the role of testosterone in driving these differences.

Children -but not chimpanzees- exhibit ‘over-imitation’, i.e. they show a propensity for faithfully copying demonstrated actions, even when these actions are irrelevant for achieving a demonstrated outcome

The social side of imitation in human evolution and development: Shared intentionality and imitation games in chimpanzees and 6-month old infants. Gabriela-Alina Sauciuc, Tomas Persson, Elainie Alenkaer Madsen. Proceedings of the 13h SEWCOG Conference 2017, Uppsala.

Imitation is generally acknowledged as a key mechanism of social learning, foundational to the emergence of human culture. By enabling quick and high-fidelity copying of others’ actions, imitation mediates the cross-generational transfer of knowledge and skills (e.g. Nielsen, 2009). Besides this ‘learning’ (or ‘cognitive’) function, imitation accomplishes also important social-communicative functions, by facilitating social interaction and promoting prosociality (e.g. Duffy & Chartrand 2015; Eckerman, Davis, & Didow, 1989; Užgiris, Benson et al., 1989). The social function of imitation is understudied in the field of comparative psychology, or even claimed to be absent in nonhuman primates. This claim, however, is grounded on how nonhuman apes (henceforth ‘apes’) perform in imitation learning experiments compared to human children. More specifically, chimpanzees exhibit lower levels of joint attention and gaze at the experimenter’s face (Carpenter & Tomasello, 1995). Moreover, children -but not chimpanzees- exhibit ‘over-imitation’, i.e. they show a propensity for faithfully copying demonstrated actions, even when these actions are irrelevant for achieving a demonstrated outcome. Such differences, it has been argued, derive from the fact that, in imitation contexts, children are motivated by a need to belong, to engage socially and to promote shared experiences (Carpenter & Call 2009; Nielsen 2009). In turn, these differences in social motivation are taken to account for the profound differences that exist between human and nonhuman primate cultures (Over & Carpenter 2012).Based on evidence from social, developmental and comparative psychology, we have recently proposed a broader definition of the social-communicative function of imitation (Persson, Sauciuc, & Madsen, 2017), that encompasses reactive and non-intentional phenomena (e.g. nonconscious mimicry, imitation-induced prosociality), as well as proactive and arguably intentional phenomena, such as social conformism or the communicative imitation documented in preverbal toddlers (e.g. Eckerman, Davis, & Didow, 1989; Eckerman & Stein, 1990). All these phenomena have been documented in nonhuman primates: nonconscious mimicry in the form of postural congruence (Jazrawi, 2000), facial mimicry (Scopa & Palagi, 2016), interactional synchrony (Yu and Tomonaga, 2016) and contagious yawning (Madsen, Persson, et al., 2013), imitation-induced prosociality expressed by increased levels of attention, proximity and object exchange after exposure to being imitated (e.g. Paukner, Suomi et al., 2009), social conformism in the form of a preference for a group-adopted procedure even when it went against a prefered or more efficient one (Hopper, Schapiro, et al., 2011), and communicative imitation in the form of familiar-action imitation used to engage or maintain interaction (Persson, Sauciuc, & Madsen, 2017).

In this presentation, we address the presence of shared intentionality in imitative contexts with evidence from four experimental studies that our team has conducted with 6-month old infants (Sauciuc, Madsen, et al., in prep), as well as with enculturated (Sauciuc, Persson, & Madsen, in prep) and non-enculturated (Madsen, Sauciuc, & Persson, in prep a, b) chimpanzees of various ages (infants, juveniles, adults). Common to all these studies is that the participants have been exposed to an imitation condition in which the experimenter imitated all their actions, as well as to a number of control conditions that varied in agreement with the specific aims of each study. In Sauciuc, Madsen et al. (in prep), to establish if 6-month old infants discriminate being imitated from contingent responding, and to examine likely mechanisms that mediate this process, infants interacted with an experimenter who (i) imitated all infant’s action ipsilaterally; (ii) imitated all infant’s actions contralaterally; (iii) imitated with a still-face, i.e. imitated bodily but not facial actions; or (iv) responded with the infant’s actions contingently but with different actions. In Madsen, Sauciuc, & Persson (in prep a), to track the ontogenetic course of imitation recognition in chimpanzees, we replicated Haun and Call’s (2008) study on imitation recognition in adult apes and exposed infant and juvenile chimpanzees to four types of interaction in which the experimenter either (i) imitated all chimpanzee’s actions; (ii) responded to the chimpanzee’s actions with temporally contingent but different actions; (iii) produced actions that were not related to the chimpanzee’s actions; (iv) sat still. In Sauciuc, Persson, & Madsen (in prep) four additional control conditions were administered in order to ascertain that behavioural indicators of shared intentionality (e.g. imitation games, laughter) could not be attributed to alternative factors known to increase playfulness in chimpanzees, including non-play species-specific behaviours, species-specific play forms (chase) or facial expressions that accompany play. Finally, in Madsen, Sauciuc, & Persson (in prep b), chimpanzees were exposed to bouts of (i) imitation, (ii) non-imitative play and (iii) no action in order to investigate the effects of imitation and non-imitative play on subsequent intentional imitation of non-instrumental actions and nonconscious mimicry (such as contagious yawning). To examine the presence of shared intentionality in the studied populations, we focused on the presence of testing behaviours and imitation games, as well as on the presence of smiling and laughter during such responses.

Users use flattering interaction information such as “Likes” for social comparison; downward comparison elicits positive & upward comparison negative emotional affect; likability of the other more strongly predicted decisions to give a “Like” than comparison outcome

“Likes” as social rewards: Their role in online social comparison and decisions to like other People's selfies. Astrid M. Rosenthal-von der Pütten et al. Computers in Human Behavior,

•    SNS users use flattering interaction information such as “Likes” for social comparison.
•    Downward comparison elicits positive and upward comparison negative emotional affect.
•    The likability of the other more strongly predicted decisions to give a “Like” than comparison outcome.

Abstract: It has been argued that reported negative effects of social networking site use on well-being and depression might be due to the vast opportunities for unflattering social comparison on Facebook. Social media websites offer Likes, a numeric representation of social acceptance, as a form of “online social currency,” which can be seen as a secondary reinforcer that drives people's tendency to compare with others. Against this background, we present an experimental study (n = 118) in which participants saw and evaluated their own selfies and selfies of other people with and without Likes. Moreover, they saw two selfies with the respective number of Likes in direct (favorable or unfavorable) comparison, and indicated their emotional state and whether they would like the other person's selfie. Results demonstrate that Likes are used for comparisons with the expected affective outcome. Like decisions, however, were rather based on judgments of likability, admiration and positive feelings after comparison rather than the comparison outcome.