Final answer:
The long necks of giraffes can be explained by both the food competition hypothesis and the sexual competition hypothesis, as traits can evolve for multiple reasons through natural selection and sexual selection.
Step-by-step explanation:
The debate over the reason for the long necks of giraffes involves evaluating multiple hypotheses, including the food competition hypothesis and the sexual competition hypothesis. The idea here is that these hypotheses are not necessarily mutually exclusive and can both contribute to the observed trait of long necks in giraffes. The food competition hypothesis suggests that giraffes with longer necks could access food resources that others could not, making them more likely to survive and reproduce. In contrast, the sexual competition hypothesis posits that the long neck might also play a role in male giraffes' fighting over mates, with longer necks providing an advantage in such contests.
Scientific evidence supports the conclusion that multiple factors can contribute to the evolution of a trait. Therefore, the correct answer is C, which acknowledges that long necks could be evolutionary advantageous for more than one reason. This is supported by the concepts of natural selection and sexual selection, both of which may act on different aspects of an organism's traits to shape evolutionary outcomes. In the case of giraffes, both access to food and success in mating could have driven the evolution of the long neck trait over time.