Why Do Giraffes Have Long Necks?

The long neck of a giraffe (genus Giraffa) is a classic example of adaptation, which is the process by which a species becomes better suited to its environment. Giraffes use their long necks to browse foliage that is as high as six meters (20 feet) off the ground, primarily from thorny acacia trees. This ability to reach tall branches gives them access to food sources that are unavailable to other herbivores, reducing competition for food.

One older theory of why giraffes have long necks was proposed by Jean-Baptise Lamarck, who suggested that individual giraffes stretched their necks to reach higher leaves, and this trait—acquired during individual animals’ lifespans—was then passed on to their offspring. However, modern evolutionary biology attributes the origin of this trait to natural selection, whereby individuals with relatively longer necks in ancestral giraffe populations had a survival advantage and were more likely to reproduce, passing on the trait to future generations.

Giraffes’ long necks are not used only to reach food. They also play a role in giraffes’ social behavior, particularly in “necking” contests between males, which establish dominance and mating rights. In fact, some scientists have proposed that giraffes’ long necks arose because of sexual selection relating to these competitions and not because of advantages they may confer in food competition with fellow herbivores.