Final answer:
Intrasexual competition leads to aggressive behaviours and displays that contribute to natural selection by ensuring that only the fittest individuals pass on their genes, which can result in significant evolutionary changes within a species.
Step-by-step explanation:
Intrasexual competition, such as male-male competition for access to mates, may lead to the development of dramatic traits and behaviours that increase an individual's chances of reproductive success. These can include aggressive behaviours or displays, such as rams butting heads, with the victor winning the opportunity to mate. This form of competition is crucial in natural selection and results in traits that signify the healthiest, strongest, or most dominant individual being chosen for mating, even though such displays can consume considerable energy and sometimes reduce the individual's survival prospects.
These competitive behaviors ensure that only those with favorable characteristics are able to pass on their genes. Therefore, intrasexual competition can lead to significant evolutionary changes within a species, including increased size, strength, or elaborate traits that are indicative of an individual's fitness.