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Sleep is an essential function of human life, underlying both biological and cultural processes. Dramatic changes in sleep occur during infancy, in terms of night awakenings, which tend to diminish over time, and day/night sleep duration, with newborns sleeping up to 16-17 hours per day and gradually decreasing to 9-13 hours between 6-11 months of age. Remarkably, research indicates that changes in infant sleep are in interaction with important acquisitions in other domains of child development. In the present study, we aimed at investigating concurrent and longitudinal relations between sleep and cognitive maturation during infancy, by collecting data on 156 infants at 4 months of age and on a subsample of 103 infants at 8 months of age. Infants’ sleep was assessed through the Brief Infant Sleep Questionnaire (BISQ; Sadeh, 2004), whereas cognitive maturation was evaluated using the Developmental ProfileTM 3 (Alpern 2007). We also examined infants’ language understanding through the Italian version of the MacArthur–Bates Communicative Development Inventory (MCDI): Words and Gestures (Caselli & Casadio, 1995; Fenson et al., 1994). Finally, information about infants’ temperament and maternal practices potentially relevant for sleep quality, such as the use of a pacifier at nighttime, co-sleeping and exclusive breastfeeding, was detected. Results showed that night and day sleep were differently related to infants’ development at 4 and 8 months of age, but there were no robust longitudinal relationships.

Money represents a cornerstone of human modern economies and how money emerged as a medium of exchange is a crucial question for social sciences. Although non-human primates have not developed monetary systems, they can estimate, combine and exchange tokens. Here, we evaluated quantity-quality trade-offs in token choices in tufted capuchin monkeys as a first step in the investigation of the generalizability of tokens as reinforcers, which is a potentially relevant factor underlying the emergence of money in humans. We measured capuchins' exchange preferences when they were repeatedly provided with 10 units of three token types yielding food combinations varying in quantity and quality. Overall, capuchins maximized their quantitative payoff, preferring tokens associated with a higher food amount, rather than showing violations of rationality. However, some individuals did not maximize their qualitative payoff, possibly because of conditional valuation effects or to the choice overload phenomenon, according to which too many options reduce the accuracy of choice. Our study supports the importance of comparative research to finely analyse the multiple components shaping the economic behaviours of other species, possibly to achieve a more comprehensive, evolutionary- and ecologically based understanding of human economic behaviour.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.

In this work, we focused on testing one of the proximal mechanisms that have been proposed to explain cooperative behaviours such as the mutual exchange of goods and services in non-human primates. Specifically, we tested 'calculated reciprocity', according to which animals exchange food with conspecifics driven by the expectation of a return of the favour. We tested pairs of tufted capuchin monkeys (Sapajus spp.), a species known to readily exchange food, in three different experimental conditions. In the first condition, the partner, after receiving food from the subject in a first test phase, could reciprocate during a second test phase (Reciprocity). In the second condition, the partner did not have the possibility to reciprocate (Control). In the third condition, the experimenter gave the subject a quantity of food proportional to what the subject had given to the partner (Pseudoreciprocity). There was no difference in the amount of food transferred from the subject to the partner among the three experimental conditions. However, in the Pseudoreciprocity condition, capuchin monkeys increased the amount of food shared along successive test sessions. These findings suggest that the expectation of reciprocation did not motivate capuchin monkeys to share their food, although they were able to learn that sharing can lead to a reward.

Money represents a cornerstone of human modern economies and how money emerged as a medium of exchange is a crucial question for social sciences. Although non-human primates have not developed monetary systems, they can estimate, combine and exchange tokens. Here, we evaluated quantity-quality trade-offs in token choices in tufted capuchin monkeys as a first step in the investigation of the generalizability of tokens as reinforcers, which is a potentially relevant factor underlying the emergence of money in humans. We measured capuchins' exchange preferences when they were repeatedly provided with 10 units of three token types yielding food combinations varying in quantity and quality. Overall, capuchins maximized their quantitative payoff, preferring tokens associated with a higher food amount, rather than showing violations of rationality. However, some individuals did not maximize their qualitative payoff, possibly because of conditional valuation effects or to the choice overload phenomenon, according to which too many options reduce the accuracy of choice. Our study supports the importance of comparative research to finely analyse the multiple components shaping the economic behaviours of other species, possibly to achieve a more comprehensive, evolutionary- and ecologically based understanding of human economic behaviour.This article is part of the theme issue ‘Existence and prevalence of economic behaviours among non-human primates’.

In questo Box vengono discusse le influenze sociali che favoriscono l'apprendimento individuale nel cebo dai cornetti e l'importanza di affiancare osservazioni sul campo ad esperimenti di laboratorio e in natura.

What cues support social influences on food preference in tufted capuchins? Although vision is important for food discrimination, we hypothesized that olfactory cues might also be involved. In Experiment 1, we assessed whether semolina flavored with a novel odor and eaten by a demonstrator, elicits more interest than semolina flavored with a familiar odor and eaten by a demonstrator, and to what extent the observer's interest towards the demonstrator was elicited by the food itself or by the odor impregnating the demonstrator's oral area. In Experiment 2, we investigated whether having encountered a novel odor in a social context increases the observer's subsequent consumption of semolina carrying this odor, versus semolina carrying another novel odor previously encountered in a non-social context. We tested fifteen demonstrator-observer pairs. 8 observers were offspring of the demonstrator; 7 observers were not offspring of the demonstrator. Offspring (but not Non-offspring) expressed interest towards the demonstrator's food significantly more when the odor was novel than familiar. Offspring (but not Non-offspring) were more interested when the demonstrator's food was present than when only its odor was available. Finally, having encountered the novel odor in the social context did not lead to greater consumption. These findings demonstrate that in closely bonded pairs foods carrying novel odors do elicit interest, although this interest is prompted mainly by the food itself. In contrast with other macrosmatic mammal species, capuchins' consumption of a food whose odor was previously encountered in a social context was not greater than that of a food whose odor was previously encountered when alone.