Evolutionary psychology and sociobiology are concerned with how natural selection has shaped the behaviour and psychology of humans and other animals. Basic concepts in genetics and evolutionary theory, necessary for applying this approach, are covered including heritability, inclusive fitness, kin selection, parental investment, parent-offspring conflict and male and female reproductive strategies. These concepts will be employed in order to understand diverse phenomena such as eusociality in bees, size and behavioural differences in males and females, the evolution of altruism and cooperation, why many species engage in sexual reproduction rather than asexual reproduction and why men and women focus on particular characteristics, such as the waist-to-hip ratio, when choosing a mate. Although many examples will be drawn from the non-human literature, the focus will be on understanding human behaviour and psychological processes.