Research Jeroen Stevens

Abstract

Similar to humans, emotions in animals affect their daily lives in many ways. While human studies rely on verbal reports for measuring subjective emotions, we need to apply a different approach for measuring animal emotions. The intensity of emotions has long been studied using behavioural and physiological measures, but these measures fail to identify the emotional valence. Positive emotions appear especially challenging to identify. Recent findings suggest that emotions also affect cognitive processes like attention, judgement and memory and that biases in these performances may give insight in the valence of experienced emotions. This project focuses on studying emotions in man's closest living relative: the bonobo. The bonobo is considered the most suitable model for reconstructing our last common ancestor and hence is a keystone species in studying our evolution and identifying unique human traits. Bonobos have rich emotional lives and respond to the emotions of others in strikingly similar ways as humans. However, the degree to which emotions of bonobos affect their own behaviour, physiology and cognition is currently unknown. To this extent, this project aims to apply a multi-componential approach to study emotions, specifically positive ones, in the bonobo using behavioural, physiological and cognitive measures. Results will be integrated to better understand emotions in bonobos and how positive emotions affect their daily lives.

Researcher(s)

• Promoter: Eens Marcel
• Co-promoter: Stevens Jeroen
• Fellow: Laméris Daan

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

The difference in cognition between humans and apes is not simply a greater degree of general intelligence, but rather a quantitative difference in social cognition. Social cognition comprises the ability to understand and respond to social responses of others. This concept includes social skills related to self-knowledge and theory of mind, which indicates the ability to understand the emotions and behavior of a person from their perspective. This project focuses on our closest living evolutionary relatives: bonobos and chimpanzees. These two species diverged from the human lineage only 5-8 mya. This makes them keystone species for investigating our own evolutionary past and identifying unique human traits. Bonobos and chimpanzees diverged from each other between 1-2 mya, but show considerable differences in social cognition. Studies in bonobos have shown that they have higher social sensitivity and are better at tasks that require social tolerance and cooperation. To date, very little is known about the mechanisms behind these behavioral differences. Therefore, this study aims to contribute to our understanding of the evolutionary origins of human sociality by studying the genetic mechanism underlying these differences in these two closely related ape species. More specifically, I aim to investigate variation in candidate genes that play an important role in the regulation of the social brain, and how they impact sociability, cooperation and social tolerance.

Researcher(s)

• Promoter: Eens Marcel
• Co-promoter: Stevens Jeroen
• Fellow: Staes Nicky

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

Just like humans, animals can experience emotions like joy, excitement, sadness and depression. However, unlike we do in human studies, we cannot simply ask animals how they feel. Scientists have used behavioural and physiological measures to identify animal emotions. Yet, these measures are difficult to interpret and often only measure the level of arousal of the emotions, and not if it is a positive or negative emotion. New insights from scientific studies suggest that the animal emotions influence cognitive performances like: attention, memory and judgement. Studying changes in an animal's cognition can thus give information about their emotional state. The proposed research project aims to study the cognitive performance of bonobos, one of our closest living evolutionary relatives, as index for their emotional state. Furthermore, we aim to complement and validate the results from the cognitive tasks with physiological and behavioural measures. Additionally, we want to study what individual characteristics determine these emotional states by asking questions like: are female bonobos happier than males? or, are bonobos that are less sociable moodier than social bonobos? Results from this project provide the opportunity to get a view into the mind bonobos and get a better understanding of their emotions. Because the bonobo is our evolutionary cousin, this will enable us to understand the evolutionary past of human emotions.

Researcher(s)

• Promoter: Stevens Jeroen
• Fellow: Laméris Daan

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

Culture is a central theme in understanding variation between human societies and a hallmark of the human species. In recent years, culture has been identified in non-human animals as well. These accounts, however, merely evidence cultural traditions (i.e. delineated behaviours like cracking nuts with wooden instead of stone tools), while human cultures also differ from one another in terms of group-level sociality, i.e. the very proclivity to be near and interact with others. Importantly, in humans, it is not any cultural tradition, but this group-level sociality (henceforth "social culture") that results in marked variation in the expression of adaptive behaviour, e.g. cooperation. My project investigates whether differences in sociality across great ape populations can be understood in terms of "social culture" (e.g. by focusing on genetics), and whether these differences explain variation in cooperation. I will study both sanctuary- and zoo-housed populations of bonobos and chimpanzees. I will test the hypotheses that great ape groups differ in their sociality, that this variation can be ascribed to "culture", and that social groups are better poised to cooperate. Chimpanzees and bonobos are our closest living relatives, having diverged from the human lineage only 5–8 mya. As such, both species form a unique window into our evolutionary past, i.e. into gaining an understanding of the behavioural phenotype of our last common ancestor and identifying uniquely human traits.

Researcher(s)

• Promoter: Eens Marcel
• Co-promoter: Stevens Jeroen
• Fellow: van Leeuwen Edwin

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

Cooperation is a key component of social life but seems an evolutionary puzzle as it involves behaviours that benefit others. Because it often involves a cost to the actor, natural selection must have produced mechanisms to regulate cooperation to overcome any adverse effects of these costs. The main proximate mechanisms that regulate cooperation are prosociality and inequity aversion, respectively the promotor and stabiliser of cooperation. In this thesis, I study a group of bonobos (Pan paniscus) in Zoo Planckendael, combining behavioural and physiological measures in different experimental paradigms to explain the variability in these proximate mechanisms of cooperation in bonobos. Bonobos are an ideal species to study prosociality and IA. First, because they are one of our closest living relatives and studying prosociality and IA in bonobos increases our knowledge on how unique the level of prosociality and IA in humans is. Second, because bonobos have been described as 'hippies of the primate world', who are highly tolerant, prosocial, empathic and cooperative, but prosociality and inequity aversion as drivers of cooperation have not been extensively studied in this species. To study prosociality, I conducted three group experiments that differed in the payoff distribution between the actor and receiver. I used a juice provisioning experiment that had previously been used to measure prosociality in chimpanzees and I implemented two food provisioning paradigms, the prosocial choice task (PCT) and the group service paradigm (GSP). To study inequity aversion, I used the standard token exchange task. To complement the standard behavioural measures with the emotional component of inequity aversion, I also investigated a behavioural and a physiological measure of arousal. The results of all prosociality experiments showed that the Zoo Planckendael bonobos mainly behaved out of self-interest: in more than half of the juice-provisioning acts, the subject also benefitted; bonobos did not prefer the prosocial above the selfish option in the PCT and adult bonobos did not provision group members in the GSP. Thus, bonobos, like chimpanzees, behaved indifferently to the welfare of others, which contrasts with the popular image of the prosocial and food sharing bonobo, who is often portrayed as a "hippie of the primate world". I concluded that this popular image is mainly the result of an age bias in previous experimental studies. I also demonstrated that bonobos reacted to receiving less than a partner by refusing trials and moving away from the experimenter while they never refused trials when receiving more than a partner. The level of inequity aversion was influenced by the relationship quality between individuals. I showed that stronger bonded individuals were more tolerant towards inequity. Further, subjects were more aroused when receiving a better reward than a partner, suggesting that bonobos do notice when being favoured but do not respond to it behaviourally. This thesis highlights the importance of validated methodologies and provides supporting evidence for the nuanced view of the prosocial, food-sharing and tolerant hippie ape. I show that adult bonobos do not behave prosocially in food-related paradigms, which can be explained by the competitive nature around the preferred food items, and which corresponds to the food-related behaviour of bonobos in the wild. I also showed that in bonobos, like chimpanzees, the tolerance to inequity is limited to a certain level and linked to specific partners.

Researcher(s)

• Promoter: Stevens Jeroen

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

This project represents a formal research agreement between UA and on the other hand KMDA. UA provides KMDA research results mentioned in the title of the project under the conditions as stipulated in this contract.

Researcher(s)

• Promoter: Eens Marcel
• Co-promoter: Stevens Jeroen
• Co-promoter: Stevens Jeroen
• Fellow: Staes Nicky

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

In thus study intrasexual and intersexual behavioural reproductive strategies of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) will be studied in captivity and compared. On the other hand, the physiology of sperm production will be studied in both species. This will be useful to understand the differences in social organization of the of the two species.

Researcher(s)

• Promoter: Eens Marcel
• Promoter: Verheyen Rudi
• Fellow: Stevens Jeroen

Research team(s)

• Behavioural Ecology & Ecophysiology

Project type(s)

• Research Project

Abstract

In thus study intrasexual and intersexual behavioural reproductive strategies of chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) will be studied in captivity and compared. On the other hand, the physiology of sperm production will be studied in both species. This will be useful to understand the differences in social organization of the two species

Researcher(s)

• Promoter: Verheyen Rudi
• Fellow: Stevens Jeroen

Research team(s)

Project type(s)

• Research Project