A new foundation Evolutionary psychology aims to understand and describe human behaviour in the light of past and continuing selection and adaptation. For a relatively young discipline, considerable progress has been made over the past few decades. Onto the conceptual framework provided by evolutionary theory, evolutionary psychologists hang observations of human behaviour and, on the whole, there they hang very well. Whether we want to understand the nature of sex differences in psychological

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... ttributes, of dynamics within and between groups, or of variability and commonalities in how individuals choose mates, evolutionary theory imparts a rigorous, informative, and cohesive structure. It is not surprising that many notable scholars in the field originally come from biological rather than psychological disciplines, since the approaches used in the study of animal behaviour and behavioural ecology are readily transferred to investigations of our own species. What is perhaps more remarkable is the extent to which many with a psychology background have come to recognize the explanatory power of evolution in their own research, and embrace it, even though they often lack formal exposure to evolutionary reasoning because many psychology departments have, at least until recently, failed to offer it. It is true that there remain numerous critics and sceptics, or worse, those that simply do not see how evolution is relevant to psychology. Increasingly, however, and as misconceptions about what evolutionary psychologists do and think are rebutted and clarified (for recent examples, see Dunbar 2008; Confer et al. 2010 ), ideas about selection and adaptation are taking root in all of the various psychological subdisciplines (Fitzgerald and Whitaker 2010 ). As Dunbar ( 2008 ) has argued, this is because evolutionary theory is a 'single seamless framework' capable of spanning disciplinary divides, and it is the only such framework we have. To many, then, Darwin's (1859, p. 449) prediction that 'Psychology will be built on a new foundation' appears to have been realized; at the very least, the foundation stone is laid and the builders have been booked. Evolutionary psychologists argue that a comprehensive understanding of any aspect of human behaviour cannot be achieved without due consideration of the selective forces that have shaped that behaviour in our evolutionary past, and which may continue to do so in the present. One way to characterize their approach is to say that they are particularly interested in the ultimate explanations for behaviour, according to the scheme set out by the renowned ethologist Niko Tinbergen ( 1963 ). Mechanistic, or proximate , explanations for the problem of why we need to eat food (e.g. 'I eat because low blood sugar levels activate neurons in the lateral hypothalamus, producing the perception of hunger') provide part of the answer, but are incomplete without information about the evolutionarily functional significance of eating (e.g. 'I eat because food provides the energy I need to survive and reproduce'). To take another example, recently expounded by Nettle ( 2011 ) , we can attempt to understand why women tend to vary in timing of the onset of their reproductive career depending upon the harshness of the environment in which they live. A functional 01-Roberts-Ch01.indd 1 01-Roberts-Ch01.indd 1