Rachna B. Reddy's research while affiliated with Harvard University and other places

Publications (17)

Article
Viral infection is a major cause of ill health in wild chimpanzees (Pan troglodytes), but most evidence to date has come from conspicuous disease outbreaks with high morbidity and mortality. To examine the relationship between viral infection and ill health during periods not associated with disease outbreaks, we conducted a longitudinal study of w...
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Caring for others is a key feature of human behavior. Mothers, fathers, siblings, grandparents, and other group members provide care in the form of provisioning, protection, and first aid. To what extent is other-regarding behavior present in our primate relatives? Here we describe an unusual incident of other-regarding behavior toward an injured j...
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Many animals engage in sociosexual behaviour, including that between same-sex pairs. Bonobos ( Pan paniscus ) are famous for their sociosexual behaviour, but chimpanzees ( Pan troglodytes ) apparently do not engage in sociosexual behaviour frequently. However, sociosexual behaviour in chimpanzees may have been overlooked. We observed 584 instances...
Article
Like many animals, adult male chimpanzees often compete for a limited number of mates. They fight other males as they strive for status that confers reproductive benefits and use aggression to coerce females to mate with them. Nevertheless, small-bodied, socially immature adolescent male chimpanzees, who cannot compete with older males for status n...
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Mothers provide indispensable care for infants in many mammalian species. In some long-lived species, the maternal-offspring bond persists after infancy with mothers continuing to provide resources and social support to their adult progeny. Maternal presence is associated with fitness benefits through adolescence for male chimpanzees despite the fa...
Article
Primates frequently form affiliative relationships that have important fitness consequences. Affiliative relationships between unrelated males and females are ubiquitous in humans but are not widely reported in humans' closest living relatives, chimpanzees (Pan troglodytes). Instead, adult male chimpanzees are extremely aggressive to females, using...
Article
Obligation as defined by Tomasello requires mutually capable parties, but one-sided caregiver relationships reveal its developmental and evolutionary precursors. Specifically, “coercive” emotions may prompt protective action by caregivers toward infant primates, and infants show distress toward caregivers when they appear to violate expectations in...
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When their mothers die, chimpanzees often adopt younger vulnerable siblings who survive with their care. This phenomenon has been widely reported, but few studies provide details regarding how sibling relationships change immediately following the deaths of their mothers. A disease outbreak that killed several females at Ngogo in Kibale National Pa...
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Respiratory viruses of human origin infect wild apes across Africa, sometimes lethally. Here we report simultaneous outbreaks of two distinct human respiratory viruses, human metapneumovirus (MPV; Pneumoviridae: Metapneumovirus) and human respirovirus 3 (HRV3; Paramyxoviridae; Respirovirus, formerly known as parainfluenza virus 3), in two chimpanze...
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Among some haplorhine primates, including humans, relaxed yawns spread contagiously. Such contagious yawning has been linked to social bonds and empathy in some species. However, no studies have investigated contagious yawning in strepsirhines. We conducted an experimental study of contagious yawning in strepsirhines, testing ring-tailed and ruffed...
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Dominance hierarchies are a prominent feature of the lives of many primate species. These hierarchies have important fitness consequences, as high rank is often positively correlated with reproduction. Although adult male chimpanzees strive for status to gain fitness benefits, the development of dominance relationships is not well understood. While...
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We tested five lemur species-ring-tailed lemurs, ruffed lemurs, mongoose lemurs, black lemurs, and Coquerel's sifakas-(N = 52) in an experiment that evaluated skills for inhibitory control in a social context. First, two human experimenters presented identical food rewards; the "generous" experimenter allowed the subject to eat from her hand, where...
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Cognition presents evolutionary research with one of its greatest challenges. Cognitive evolution has been explained at the proximate level by shifts in absolute and relative brain volume and at the ultimate level by differences in social and dietary complexity. However, no study has integrated the experimental and phylogenetic approach at the scal...
Data
The procedure for Experiment 1. (MOV)
Article
Full-text available
The social intelligence hypothesis suggests that living in large social networks was the primary selective pressure for the evolution of complex cognition in primates. This hypothesis is supported by comparative studies demonstrating a positive relationship between social group size and relative brain size across primates. However, the relationship...
Data
Supplemental analyses, Table S1, and Figure S1. (DOCX)
Data
The procedure for Experiment 2. (M4V)

Citations

... Species differences in social bonds likely also shape species differences in gestural communication networks: who communicates with whom and about what. Depending on species, social bonds may be mediated through cooperative behaviours, such as hunting, food sharing (e.g., chimpanzees: Wittig et al. 2014;Samuni et al. 2018aand bonobos: Fruth & Hohmann et al. 2002Goldstone et al. 2016), and border patrols (West African chimpanzees, Samuni et al. 2019), or other forms of social interactions such as grooming and socio-sexual behaviour (chimpanzees: e.g., Crockford et al. 2013;Sandel & Reddy 2021; bonobos: e.g., Moscovice et al. 2019;gorillas: Yamagiwa 1992;Robbins 2010;. Chimpanzees tend to have strong male-male social bonds and weaker female-female social bonds; however, female social bond strength is variable across subspecies with a tendency for weaker bonds in East African compared to West African chimpanzees (Yamakoshi 2004;Lehmann & Boesch 2008). ...
... when mating with low-ranking males, chimpanzee females typically refrain from producing copulation calls, presumably to remain concealed and so avoid attracting attention and eventual aggression 17 . Second, the presence of a focal male's mother also appeared to have a negative effect, which is difficult to interpret but suggests that mother-son relationships have an impact on how males interact with other females 48 . Due to small sample size and large variation between subjects, we can only speculate regarding this effect. ...
... In such context, male-female aggressive rates are more likely to reflect the existence of such differentiated social bonds between males and females than a scenario where a male would attack females who randomly happen to stand in their proximity. In line with this, recent studies in chimpanzees indicate that males preferably coerce their affiliated female partners (Reddy and Mitani, 2020), mirroring observations in humans where intimate partner violence is extensive (Basile, 2002). ...
... Although caregiving and other-regarding preferences may be most extensive in humans, precursors of these behaviors can be found in other animals (Hart 2011;Preston 2013). Caregiving behaviors such as carrying, provisioning, grooming, and agonistic support have been observed in one of our closest relatives, chimpanzees (Pan troglodytes), including toward vulnerable young whose mothers are ill (Uehara and Nyundo 1983;Huffman and Seifu 1989), injured (Pruetz 2011), or deceased (Hobaiter et al. 2014;Nakamura and Hosaka 2015;Reddy and Mitani 2019;Samuni et al. 2019). Chimpanzees occasionally attend to the wounds of groupmates, including removing splinters in captivity (Köhler 1925;Yerkes 1943) and grooming or licking wounds in the wild (Goodall 1983(Goodall , 1986Boesch 1991). ...
... Respiratory diseases of viral or bacterial origin were the most extensively studied. This is not surprising, considering that respiratory infections are the main cause of morbidity and mortality in wild chimpanzees and gorillas in many settings [34]. Of note, viruses that are relatively benign in humans (e.g., human rhinovirus C) can cause lethal outbreaks in ape populations, indicating poor host adaptation and a lack of resistance in apes [34]. ...
... At the time of the study, the chimpanzee community consisted of approximately 195 individuals. We focused on a subset of 18 adolescent and adult male chimpanzees between 12 and 20 years old, as these were the subjects of a concurrent behavioral study (Sandel et al. 2017(Sandel et al. , 2020. Given that Ngogo chimpanzees at age 12 and 13 years appear considerably smaller than adult male chimpanzees, we expected to detect differences in size between the former and the latter. ...
... In particular, the reflexive tendency to yawn following the detection of yawns in others, i.e., contagious yawning, is a well-documented phenomenon that may serve to enhance vigilance and synchronization in groups [19]. Distinct from physiologically triggered yawns, which are ubiquitous in vertebrates, there is a great deal of variation across species when it comes to the tendency to yawn contagiously [20][21][22][23]. ...
... However, a recent study found no difference in spatial memory task performance on the Primate Cognition Test Battery between frugivorous Varecia, insectivorous-omnivorous Microcebus (mouse lemurs) and omnivorous Lemur (Fichtel et al., 2020). Further, Varecia, Lemur, Propithecus and Eulemur did not differ when tested on social inhibitory control abilities (Reddy et al., 2015). Partially due to dietary variation, lemur species have also been found to differ in locomotor modes and positional behavior, which impacts body control and the manual dexterity needed in some cognitive tasks (Peckre et al., 2016;Batist and Mayhew, 2020). ...
... Self-control is another cognitive ability to be enhanced when the degree of fission-fusion dynamics is high [88]. ...
... As more data become available and methods improve further, broad-scale comparative brain size studies will still offer novel and valuable insights into cognitive evolution [86]. However, we suggest that for a more nuanced understanding of the drivers of cognitive evolution we must also test how uncertainty in the social and ecological environment influences cognitive performance at the intra-specific level [84,[87][88][89], and between closely related species [90][91][92][93][94]. Conceptually, we also recommend a shift away from the treatment of the SIH and EIH as dichotomous and competing hypotheses. ...