Final answer:
Giraffes with longer necks are an example of natural selection, where they gained an evolutionary advantage by reaching higher leaves for food, increasing their chances of survival and reproduction.
Step-by-step explanation:
Male giraffes with a longer neck are able to reach more food and thus survive longer and reproduce more. This results in the evolution of long necks due to natural selection.
LibreTexts™ explains this evolutionary phenomenon, indicating that giraffes with longer necks had an advantage in that they could reach leaves other giraffes could not. This greater fitness allowed them to survive, reproduce, and pass the long-neck trait to their offspring. With each generation, more long-necked giraffes were present until eventually, all giraffes had long necks.
Sources such as the Galápagos Archipelago's tortoise population observations by Darwin support this concept. Tortoises with longer necks could reach more food, especially during droughts, leading them to have higher reproductive success and, over time, resulting in a population of only long-necked tortoises.
Genetic drift can also influence certain traits within a population, but the scenario described for the giraffes is more representative of the principles of natural selection, where traits beneficial for survival and reproduction become more common.