One standout feature of human language is our ability to reference external objects and events with socially learned symbols, or words. Exploring the phylogenetic origins of this capacity is therefore key to a comprehensive understanding of the evolution of language. While non-human primates can produce vocalizations that refer to external objects in the environment, it is generally accepted that their acoustic structure is fixed and a product of arousal states. Indeed, it has been argued that the apparent lack of flexible control over the structure of referential vocalizations represents a key discontinuity with language. Here, we demonstrate vocal learning in the acoustic structure of referential food grunts in captive chimpanzees. We found that, following the integration of two groups of adult chimpanzees, the acoustic structure of referential food grunts produced for a specific food converged over 3 years. Acoustic convergence arose independently of preference for the food, and social network analyses indicated this only occurred after strong affiliative relationships were established between the original subgroups. We argue that these data represent the first evidence of non-human animals actively modifying and socially learning the structure of a meaningful referential vocalization from conspecifics. Our findings indicate that primate referential call structure is not simply determined by arousal and that the socially learned nature of referential words in humans likely has ancient evolutionary origins.

We welcome the correspondence from Fischer and colleagues regarding our recent paper on vocal learning in chimpanzee food grunts [1]. Fischer et al. make two challenges to our paper's conclusions, which we address here.

a b s t r a c tWhether the opportunity to breed and rear young improves the welfare of captive animals is currently debated. However, there is very little empirical data available to evaluate this relationship and this study is a first attempt to contribute objective data to this debate. We utilized the existing variation in the reproductive experiences of sanctuary chimpanzees at Chimfunshi Wildlife Orphanage Trust in Zambia to investigate whether breeding and rearing young was associated with improved welfare for adult females (N = 43). We considered several behavioural welfare indicators, including rates of luxury behaviours and abnormal or stress-related behaviours under normal conditions and conditions inducing social stress. Furthermore, we investigated whether spending time with young was associated with good or poor welfare for adult females, regardless of their kin relationship. We used generalized linear mixed models and found no difference between adult females with and without dependent young on any welfare indices, nor did we find that time spent in proximity to unrelated young predicted welfare (all fullnull model comparisons likelihood ratio tests P > 0.05). However, we did find that coprophagy was more prevalent among mother-reared than non-mother-reared individuals, in line with recent work suggesting this behaviour may have a different etiology than other behaviours often considered to be abnormal. In sum, the findings from this initial study lend support to the hypothesis that the opportunity to breed and rear young does not provide a welfare benefit for chimpanzees in captivity. We hope this investigation provides a valuable starting point for empirical study into the welfare implications of managed breeding.

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A correlational study examined the relationship between hypnotic suggestibility and academic achievement. Fifty-eight undergraduate students were administered the HGSHS:A (Shor and Orne, 1962) and their assessment grades from a range of taught modules were collected. Significant negative correlations were found, showing that the higher the academic achievement, the lower the hypnotic suggestibility. Multiple regression found that academic grades were signif icant predictors of hypnotic suggestibility. The implications are discussed.