In this article, I review the literature to determine how successful the latent trait theory model of personality from differential psychology has been for studying personality in non-human primates. The evidence for the success of this model is quite good, and offers insights and directions for personality research in primates and other animals. This, I conclude, stems from (i) the human trait model's simplicity, and (ii) the fact that the human differential model of personality developed in the face of harsh criticism, which led researchers to test and refine their models.
Animal models of human behaviour and vice versaThe question of whether studies of human behaviour can contribute to the understanding of behavioural evolution is an old one, and the debate that it has engendered is ongoing. In this paper, I will show that using a 'human model' of personality, developed within differential psychology, to study the evolutionary origins of individual differences in behaviour, affect and cognition (i.e. personality) in non-human primates (from now on, primates) has been a successful enterprise. Moreover, in a move that I hope does not distress the editors, I will sidestep answering directly the question posed by this special issue. Instead, I will describe why the human model is useful for studying primate personality and how it came to be that way.Before discussing human models, I will present an overview of animal models. Animal models have been an important and powerful tool for learning about the evolutionary origins of humans behaviour [1]. One would think then that critics of this model would be limited to the likes of creationists [2]. Unfortunately, displeasure and discomfort with the notion that we can learn about our behaviour and its evolution by studying animals has not been limited to people outside the purview of evolutionary biology. For example, because he viewed them as excusing human vices, such as sexism, Stephen J. Gould wrote essays for scientific and lay audiences that criticized adaptationist explanations for human behaviour that were based on studies of animals [3].To some, the use of human models to understand animal behaviour is also controversial. Using humans as models to understand the evolutionary bases of behaviour has a history that dates back at least as far as the use of animal models. The use of human models is rooted in the notion that evolution is gradual, and so related species will tend to be similar [4]. Prominent examples of the use of human models in the history of comparative psychology include Wolfgang Kö hler's investigations into the intelligence of chimpanzees [5], and work by Robert Yerkes [6] and his colleagues, Donald Hebb [7] and Meredith Crawford [8], on chimpanzee personality. These and similar pursuits continue into the present day, and have been enjoined by others (see articles in this special issue).The view that human behaviour can inform us about animal behaviour has been criticized by biologists and psychologists. One criticism is that the use of human m...