Evolutionary explanations of aggression suggest that aggression serves an important function in terms of both individual survival as well as reproductive potential. Competition arises when resources are limited and animals must compete in order to survive and reproduce. Some behaviours, such as aggression, would have made it more likely that our ancestors survived and passed on their genes. This means that aggression has an adaptive purpose because it facilitates survival and adaptation to the environment. Males who used aggression would have been successful in securing and retaining mates, as they could fight any rivals and prevent their mates from sexual infidelity; consequently, they would be more likely to pass on their genes.