Final answer:
Male deer on the Scottish island of Rum have larger antlers primarily for competition with other males to access females, an example of sexual selection. These antlers serve in sexual dimorphism and natural selection, demonstrating the evolutionary benefits outweighing their physical costs.
Step-by-step explanation:
On the Scottish island of Rum, male deer, or stags, have larger antlers which they primarily use to compete with other males for access to females. This is a form of sexual selection, where antlers serve as a means for a male to secure mating rights through displays of strength in contests with other males or by attracting females due to the impression of greater fitness. Large antlers may also play a role in defending territories that have enough resources to support the stags and their offspring.
The phenomenon where males develop prominent features to attract females is referred to as sexual dimorphism. In the animal kingdom, these features can influence a male's reproductive success because they may increase their chances to mate with more females. The antlers can also serve as a visual deterrent to other males, indicating that a stag is strong and capable of defending his territory and potential mating partners.
While the antlers are costly to grow and maintain, as they use a significant amount of energy and can get entangled in vegetation, this cost is outweighed by the reproductive advantages they provide. Therefore, antler growth is favoured by natural selection. Ultimately, these traits have evolved over generations through the process of natural selection—those stags with larger antlers typically have a higher mating success, thereby passing on their genetics to the next generation.