Why the long neck?

Why did giraffes evolve such long necks?
 Image credit: Bernard Dupont

The incredibly long neck of the giraffe is a well known characteristic. Hypotheses for the giraffes long neck started flying about in the 1800s, with scientists Lamarck and Darwin both producing competing hypotheses. Whilst Lamarck's ideas about neck stretching have been thrown out the window, Darwin's "competing browsers" hypothesis has continued to be a strong contender. 

The "competing browsers" hypothesis proposes that giraffes necks evolved through natural selection to reduce competition with other foliage consumers in the environment. Naturally occurring (but small) differences in giraffe neck lengths, allowed those with the longest necks to reach leaves that were out of reach to other species (and shorter necked giraffe ancestors). Growing taller may have helped both sexes increase their browsing (until a certain height ~2.5-3 m) but it is often found that individuals still feed at shoulder height. 

In 1996 a new hypothesis emerged, that of the "Necks for Sex". This hypothesis suggested that the ridiculously long giraffe neck may owe its origins or continued maintenance to sexual selection. It is very obvious that males today use their necks for fighting rival males, both over territories and access to females. 

In some cases a trait that has arose for one purpose, has since been 'hijacked' for another purpose. This may be the case for the giraffes long neck. Evidence is suggestive of a variety of factors for the origin and maintenance of the giraffes neck but further study is needed. It is unlikely that the selection pressure on the origin of the neck is the same as the maintenance pressures today.

Find Out More:
VIDEO: Giraffe Fight - Some amazing footage from the recent BBC series 'Africa' narrated by David Attenborough

Sources:

• SIMMONS, R. E & ALTWEGG, R. 2010. Necks-for-sex or competing browsers? A critique of ideas on the evolution of giraffe. Journal of Zoology, 282, 6-12