The study of animal behaviour begins with understanding how an animal's physiology and anatomy are integrated with its behavioural patterns. Both external and internal stimuli prompt behaviours e.g., threats from other animals, sounds, smells or weather and internal information e.g., hunger, fear etc. Understanding how genes and the environment come together to shape animal behaviour is also an important underpinning of the field. Genes capture the evolutionary responses of prior populations to selection on behaviour. Environmental flexibility gives animals the opportunity to adjust to changes during their own lifetime. Scientists are drawn to the study of animal behaviour for varied reasons and the field is extremely broad, ranging from research on feeding behaviour and habitat selection to mating behaviour and social organizations. Many scientists study animal behaviour because it sheds light on human beings. Research on non-human primates, for instance, continues to offer valuable perspectives into the causes and evolution of individual, social, and reproductive human actions. Understanding why some animals help others at the potential cost of their own survival and reproduction, for example, not only gives us insight into their behaviour but could also help us to understand the underpinnings of our ideas of altruism and sacrifice.