@article{ross_hooper_smith_jaeggi_smith_gavrilets_zohora_ziker_xygalatas_wroblewski_et al._2023, title={Reproductive inequality in humans and other mammals}, volume={120}, ISSN={["1091-6490"]}, DOI={10.1073/pnas.2220124120}, abstractNote={To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women’s fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species—including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.}, number={22}, journal={PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA}, author={Ross, Cody T. and Hooper, Paul L. and Smith, Jennifer E. and Jaeggi, Adrian V. and Smith, Eric Alden and Gavrilets, Sergey and Zohora, Fatema tuz and Ziker, John and Xygalatas, Dimitris and Wroblewski, Emily E. and et al.}, year={2023}, month={May} }
 @article{feldblum_boehm_walker_pusey_2022, title={Predictors and consequences of gestation length in wild chimpanzees}, ISSN={["2692-7691"]}, DOI={10.1002/ajpa.24601}, abstractNote={Abstract}, journal={AMERICAN JOURNAL OF BIOLOGICAL ANTHROPOLOGY}, author={Feldblum, Joseph T. and Boehm, Emily E. and Walker, Kara K. and Pusey, Anne E.}, year={2022}, month={Aug} }
 @article{bowie_walker_bunnell_morel_minesi_belais_hare_2021, title={Assessing conservation attitudes and behaviors of Congolese children neighboring the world's first bonobo (Pan paniscus) release site}, volume={83}, ISSN={["1098-2345"]}, DOI={10.1002/ajp.23217}, abstractNote={Abstract}, number={1}, journal={AMERICAN JOURNAL OF PRIMATOLOGY}, author={Bowie, Aleah and Walker, Kara and Bunnell, Gabrielle and Morel, Dominique and Minesi, Fanny and Belais, Raphael and Hare, Brian}, year={2021}, month={Jan} }
 @article{walker_foerster_murray_mjungu_pusey_2021, title={Evaluating adaptive hypotheses for female-led infanticide in wild chimpanzees}, volume={180}, ISSN={["1095-8282"]}, DOI={10.1016/j.anbehav.2021.07.025}, abstractNote={Although rare among group-living primates, infanticide by females has been reported in several chimpanzee, Pan troglodytes, populations. We examined 13 infanticidal attacks over 47 years at Gombe National Park, Tanzania to evaluate three adaptive hypotheses. (1) Exploitation of the infant as a food resource – by eating a vulnerable neonate, attackers gain calories that may be important during periods of food scarcity or energetic stress. (2) Resource competition – Gombe females concentrate their foraging in overlapping core areas and dominance rank influences foraging success. By killing the infant of a female with high core area overlap, the perpetrator removes a current and future competitor, improving her access to food. (3) Low cost – female chimpanzees mature and reproduce slowly, and longevity increases reproductive success. Physical aggression causes risk of severe injury or death, so females will only mount attacks when risks to the perpetrator are low. In support of hypothesis 1, females usually consumed the carcass. However, attacks were not more likely in times of resource or energy scarcity. In support of hypothesis 2, females attacked others with whom they shared core areas, but attacks did not cause shifts in ranging patterns. In support of hypothesis 3, one or more attackers always outranked the victim, the attacks often involved coalitions and victims usually lacked kin support. Attacks were more likely to be successful when attackers were not hindered by clinging infants and victims could not retreat. Our results provide further evidence for female competition and the adaptive value of female-led infanticide in this species.}, journal={ANIMAL BEHAVIOUR}, author={Walker, Kara K. and Foerster, Steffen and Murray, Carson M. and Mjungu, Deus and Pusey, Anne E.}, year={2021}, month={Oct}, pages={23–36} }
 @article{pontzer_brown_wood_raichlen_mabulla_harris_dunsworth_hare_walker_luke_et al._2021, title={Evolution of water conservation in humans}, volume={31}, ISSN={["1879-0445"]}, DOI={10.1016/j.cub.2021.02.045}, abstractNote={To sustain life, humans and other terrestrial animals must maintain a tight balance of water gain and water loss each day.1Cheuvront S.N. Kenefick R.W. Montain S.J. Sawka M.N. Mechanisms of aerobic performance impairment with heat stress and dehydration.J Appl Physiol. 2010; 109: 1989-1995Crossref PubMed Scopus (302) Google Scholar, 2Armstrong L.E. Johnson E.C. Water Intake, Water Balance, and the Elusive Daily Water Requirement.Nutrients. 2018; 10: 1928Crossref Scopus (77) Google Scholar, 3Popkin B.M. D’Anci K.E. Rosenberg I.H. Water, hydration, and health.Nutr. Rev. 2010; 68: 439-458Crossref PubMed Scopus (499) Google Scholar However, the evolution of human water balance physiology is poorly understood due to the absence of comparative measures from other hominoids. While humans drink daily to maintain water balance, rainforest-living great apes typically obtain adequate water from their food and can go days or weeks without drinking4Wrangham R.W. Feeding behavior of chimpanzees in Gombe National Park, Tanzania.in: Clutton-Brock T.H. Primate Ecology: Studies of Feeding and Ranging Behavior in Lemurs, Monkeys, and Apes. Academic Press, 1977: 503-538Google Scholar, 5Ashbury A.M. Posa M.R. Dunkel L.P. Spillmann B. Atmoko S.S. van Schaik C.P. et al.Why do orangutans leave the trees? Terrestrial behavior among wild Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan, Central Kalimantan.Am. J. Primatol. 2015; 77: 1216-1229Crossref PubMed Scopus (23) Google Scholar, 6Rothman J.M. Dierenfeld E.S. Hintz H.F. Pell A.N. Nutritional quality of gorilla diets: consequences of age, sex, and season.Oecologia. 2008; 155: 111-122Crossref PubMed Scopus (101) Google Scholar. Here, we compare isotope-depletion measures of water turnover (L/d) in zoo- and rainforest-sanctuary-housed apes (chimpanzees, bonobos, gorillas, and orangutans) with 5 diverse human populations, including a hunter-gatherer community in a semi-arid savannah. Across the entire sample, water turnover was strongly related to total energy expenditure (TEE, kcal/d), physical activity, climate (ambient temperature and humidity), and fat free mass. In analyses controlling for those factors, water turnover was 30% to 50% lower in humans than in other apes despite humans’ greater sweating capacity. Water turnover in zoo and sanctuary apes was similar to estimated turnover in wild populations, as was the ratio of water intake to dietary energy intake (∼2.8 mL/kcal). However, zoo and sanctuary apes ingested a greater ratio of water to dry matter of food, which might contribute to digestive problems in captivity. Compared to apes, humans appear to target a lower ratio of water/energy intake (∼1.5 mL/kcal). Water stress due to changes in climate, diet, and behavior apparently led to previously unknown water conservation adaptations in hominin physiology.}, number={8}, journal={CURRENT BIOLOGY}, author={Pontzer, Herman and Brown, Mary H. and Wood, Brian M. and Raichlen, David A. and Mabulla, Audax Z. P. and Harris, Jacob A. and Dunsworth, Holly and Hare, Brian and Walker, Kara and Luke, Amy and et al.}, year={2021}, month={Apr}, pages={1804-+} }
 @misc{walker_pusey_2020, title={Inbreeding risk and maternal support have opposite effects on female chimpanzee dispersal}, volume={30}, ISSN={["1879-0445"]}, DOI={10.1016/j.cub.2019.11.081}, abstractNote={Sex-biased dispersal is usually driven by a combination of inbreeding avoidance and intrasexual competition. Walker and Pusey show that dispersal decisions in chimpanzees are most influenced by inbreeding avoidance and kin cooperation, instead of competition.}, number={2}, journal={CURRENT BIOLOGY}, author={Walker, Kara K. and Pusey, Anne E.}, year={2020}, month={Jan}, pages={R62–R63} }
 @article{muller_jones_colchero_thompson_enigk_feldblum_hahn_langergraber_scully_vigilant_et al._2020, title={Sexual dimorphism in chimpanzee (Pan troglodytes schweinfurthii) and human age-specific fertility}, volume={144}, ISSN={["0047-2484"]}, DOI={10.1016/j.jhevol.2020.102795}, abstractNote={Across vertebrates, species with intense male mating competition and high levels of sexual dimorphism in body size generally exhibit dimorphism in age-specific fertility. Compared with females, males show later ages at first reproduction and earlier reproductive senescence because they take longer to attain adult body size and musculature, and maintain peak condition for a limited time. This normally yields a shorter male duration of effective breeding, but this reduction might be attenuated in species that frequently use coalitionary aggression. Here, we present comparative genetic and demographic data on chimpanzees from three long-term study communities (Kanyawara: Kibale National Park, Uganda; Mitumba and Kasekela: Gombe National Park, Tanzania), comprising 581 male risk years and 112 infants, to characterize male age-specific fertility. For comparison, we update estimates from female chimpanzees in the same sites and append a sample of human foragers (the Tanzanian Hadza). Consistent with the idea that aggressive mating competition favors youth, chimpanzee males attained a higher maximum fertility than females, followed by a steeper decline with age. Males did not show a delay in reproduction compared with females, however, as adolescents in both sites successfully reproduced by targeting young, subfecund females, who were less attractive to adults. Gombe males showed earlier reproductive senescence and a shorter duration of effective breeding than Gombe females. By contrast, older males in Kanyawara generally continued to reproduce, apparently by forming coalitions with the alpha. Hadza foragers showed a distinct pattern of sexual dimorphism in age-specific fertility as, compared with women, men gained conceptions later but continued reproducing longer. In sum, both humans and chimpanzees showed sexual dimorphism in age-specific fertility that deviated from predictions drawn from primates with more extreme body size dimorphism, suggesting altered dynamics of male-male competition in the two lineages. In both species, coalitions appear important for extending male reproductive careers.}, journal={JOURNAL OF HUMAN EVOLUTION}, author={Muller, Martin N. and Jones, Nicholas G. Blurton and Colchero, Fernando and Thompson, Melissa Emery and Enigk, Drew K. and Feldblum, Joseph T. and Hahn, Beatrice H. and Langergraber, Kevin E. and Scully, Erik J. and Vigilant, Linda and et al.}, year={2020}, month={Jul} }
 @article{walker_walker_goodall_pusey_2018, title={Maturation is prolonged and variable in female chimpanzees}, volume={114}, ISSN={["0047-2484"]}, DOI={10.1016/j.jhevol.2017.10.010}, abstractNote={Chimpanzees are important referential models for the study of life history in hominin evolution. Age at sexual maturity and first reproduction are key life history milestones that mark the diversion of energy from growth to reproduction and are essential in comparing life history trajectories between chimpanzees and humans. Yet, accurate information on ages at these milestones in wild chimpanzees is difficult to obtain because most females transfer before breeding. Precise age at first birth is only known from a relatively small number of non-dispersing individuals. Moreover, due to small sample sizes, the degree to which age at maturation milestones varies is unknown. Here we report maturation milestones and explore sources of variance for 36 wild female chimpanzees of known age, including eight dispersing females born in Gombe National Park, Tanzania. Using Kaplan-Meier survival analysis, including censored intervals, we find an average age of 11.5 years (range 8.5–13.9) at sexual maturity and 14.9 years (range 11.1–22.1) at first birth. These values exceed previously published averages for wild chimpanzees by one or more years. Even in this larger sample, age at first birth is likely underestimated due to the disproportionate number of non-dispersing females, which, on average, give birth two years earlier than dispersing females. Model selection using Cox Proportional Hazards models shows that age at sexual maturity is delayed in females orphaned before age eight years and those born to low-ranking mothers. Age at first birth is most delayed in dispersing females and those orphaned before age eight years. These data provide improved estimates of maturation milestones in a population of wild female chimpanzees and indicate the importance of maternal factors in development.}, journal={JOURNAL OF HUMAN EVOLUTION}, author={Walker, Kara K. and Walker, Christopher S. and Goodall, Jane and Pusey, Anne E.}, year={2018}, month={Jan}, pages={131–140} }
 @article{walker_walker_paulo_pusey_2018, title={Morphological Identification of Hair Recovered from Feces for Detection of Cannibalism in Eastern Chimpanzees}, volume={89}, ISSN={["1421-9980"]}, DOI={10.1159/000488509}, abstractNote={Chimpanzees (Pan troglodytes) are primarily frugivorous but consume a variable amount of meat from a variety of organisms, including other chimpanzees. Cannibalism is rare, usually follows lethal aggression, and does not occur following natural deaths. While chimpanzee cannibalism has been documented at multiple sites, many instances of this behavior go unrecorded. Identification of chimpanzee remains in feces, however, can provide indirect evidence of cannibalism. Hair, in particular, typically passes through the gastrointestinal tract undamaged and is commonly used for purposes of identification in wildlife forensics. Here we test the hypothesis that eastern chimpanzee (Pan troglodytes schweinfurthii) guard hair morphology can be reliably distinguished from the hairs of their most common prey species. Methods and results are presented in the context of a case study involving a suspected chimpanzee infanticide from Gombe, Tanzania. We find that chimpanzee guard hair morphology is unique among tested mammals and that the presence of abundant chimpanzee hair in feces is likely the result of cannibalism and not incidental ingestion from grooming or other means. Accordingly, morphological analysis of guard hairs from feces is a promising, cost-effective tool for the determination of cannibalistic acts in chimpanzees.}, number={3-4}, journal={FOLIA PRIMATOLOGICA}, author={Walker, Christopher S. and Walker, Kara K. and Paulo, Gabo and Pusey, Anne E.}, year={2018}, pages={240–250} }
 @article{tan_walker_hoff_hare_2018, title={What influences a pet dog's first impression of a stranger?}, volume={46}, ISSN={["1543-4508"]}, DOI={10.3758/s13420-018-0353-y}, abstractNote={Dogs live in the dynamic human social networks full of strangers, yet they form strong and selective bonds with familiar caretakers. Little is known about how a bond is initially formed between a dog and a complete stranger. The first-impression hypothesis suggests that interacting with strangers can present an opportunity to form a mutualistic partnership. It predicts that dogs should respond positively toward a complete stranger to facilitate bonding (Prediction 1) and adjust their preferences in response to the perceived risk and benefit of interacting with strangers (Prediction 2). We examine the social preferences of pet dogs toward a complete stranger whom they have never met before and several other potential partners – the owner with whom subjects have had a positive, long-term bond (Experiment 1), and an exposed stranger with whom they have had a positive short-term interaction (Experiment 2) or a negative one (Experiment 3). In support of Prediction 1, subjects were exceptionally trusting across contexts. Mixed results were found with regard to Prediction 2. Subjects preferred their owner over a stranger when following social cues and (to a lesser degree) when approaching and feeding in close proximity. However, relative to a complete stranger, subjects did not consistently prefer the positively exposed stranger or avoid the negatively exposed one. The lack of clear selectivity might be due to pet dogs’ high baseline level of trust of complete strangers or reflect the strength of their existing bonds that negated the need for another positive bond with a new human partner.}, number={4}, journal={LEARNING & BEHAVIOR}, author={Tan, Jingzhi and Walker, Kara K. and Hoff, Katherine and Hare, Brian}, year={2018}, month={Dec}, pages={414–429} }