The evolution of the extremely elongated neck of giraffes, which can be up to 2–2.4m in length, has been the subject of intense debate since the time of Darwin.
“The 'competing browsers hypothesis' was originally suggested by Charles Darwin and challenged only recently. It suggests that competitive pressure from smaller browsers, such as kudu, steenbok and impala, encouraged the elongation of the neck, as it enabled giraffes to reach food that competitors could not.”
“A 2010 study found that adult giraffes with longer necks actually suffered higher mortality rates under drought conditions than their shorter-necked counterparts. This study suggests that maintaining a longer neck requires more nutrients, which puts longer-necked giraffes at risk during a food shortage.”
Another, more recent theory, suggests that the long necks evolved because of the 'necking' contests (where males use their heads as weapons) to establish dominance and obtain access to sexually receptive females.
A third hypothesis is that the neck serves to give the animal enhanced vigilance.