Since Darwin first dictated his theory of natural selection, only one plausible hypothesis for the evolution of the giraffe's towering height could be reasoned. The long neck of the giraffe evolved to allow access to plant material unavailable to its shorter competitors. Thus, over time, interspecific competition provided enough pressure to allow the giraffe to occupy an empty niche: the tops of trees. It seems the only reasonable evolutionary explanation of a giraffe's neck must have to do with feeding . . . or is it?.
The interspecific feeding competition hypothesis for the giraffe's neck was first proposed by Darwin (Freeman and Herron 2001). In simplified form it states that the neck of giraffes evolved due to interspecific competition for food. This selective pressure over time allowed giraffe decedents with longer necks (directly correlated to food gathering abilities) to survive over those with shorter necks. After millions of years, the giraffe decedents surviving have the massive height which we see today.
Although the interspecific feeding competition hypothesis seems obvious, it lacks data to support it. Recent research done by Truman Young and Lynne Isbell (1991) shows that giraffes do not utilize their necks for food foraging as previously thought. One would expect that during drought and dry seasons when food is scarce, that a giraffe would utilize its neck to reach into the trees to graze an untapped resource. However, Young and Isbell (1991) found that over 50% of feeding took place at or below shoulder height, and only a fraction of feeding (roughly 5%) occurred at the maximum height a giraffe could reach. If a giraffe is not using its long neck for feeding, then what is it using it for?.
A New Outlook.
Robert Simmons and Lue Scheepers (1996) developed an alternate hypothesis to that of the feeding hypothesis. In their research, they concluded that a giraffe's neck was primarily used during mating as a weapon.