19Understanding the extent to which humans perceive the emotional state of animals has both 20 theoretical and practical implications. While recent studies indicate that natural selection has 21 led to some convergence of emotion coding among vertebrate species (including humans), 22highlighting the interspecific value of emotional signals, it has also been argued that 23 interspecific communication of emotions can fail due to species-specific signaling traits 24 impairing information decoding, and/or absence of familiarity with heterospecific 25 communication systems. Here we show that human listeners pay attention to the mean pitch 26 of vocalizations when asked to rate the distress level expressed by human baby cries, and that 27 they use a similar pitch scale to rate the emotional level of baby non-human ape (bonobo and 28 chimpanzee) distress calls. As a consequence the very high-pitched bonobo infant calls were 29 systematically rated as expressing overall high distress levels despite being recorded in 30 contexts eliciting various stress intensity. Conversely, chimpanzee infant calls -which are 31 characterized by a relatively lower-pitch-were systematically rated as expressing relatively 32 lower distress levels. These results indicate that, in the absence of exposure/familiarity, our 33 spontaneous ability to range the emotional content of vocalizations in closely related ape 34 species remains biased by basic frequency differences, suggesting that the absolute 35 interspecific value of emotional signals should not be over-estimated. 36 37 KEYWORDS: acoustic communication -evolutive convergence -ape -bonobo -38 chimpanzee -cry -distress call -emotion -human baby -signal. 39 3
Previous investigations of parents' abilities to recognize the cries of their own babies have identified substantial and significant sex differences, with mothers showing greater correct recognition rates than fathers. Such sex differences in parenting abilities are common in non-human mammals and usually attributed to differential evolutionary pressures on male and female parental investment. However, in humans the traditional concept of 'maternal instinct' has received little empirical support and is incongruous given our evolutionary past as cooperative breeders. Here we use a controlled experimental design to show that both fathers and mothers can reliably and equally recognize their own baby from their cries, and that the only crucial factor affecting this ability is the amount of time spent by the parent with their own baby. These results highlight the importance of exposure and learning in the development of this ability, which may rely on shared auditory and cognitive abilities rather than sex-specific innate predispositions.
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