How the giraffe got its long neck

by Greg Mayer

Matthew Cobb has kindly called my attention to this piece from the BBC about this soon to be published paper (pdf) in the Journal of Zoology by Graham Mitchell, S.J. van Sittert, and John Skinner on the neck of the giraffe. How giraffes got their long necks is a venerable question in biology, having been discussed by, among others, Lamarck , Wallace, and Darwin. The paper by Mitchell and colleagues deals with an hypothesis proposed in 1996 by Robert E. Simmons and Lue Scheepers: that the long neck of giraffes results from sexual selection by male-male competition (see chap. 6 of WEIT for a general discussion of sexual selection).  At first it may seem obvious that long necks are for reaching leaves and shoots way up in the trees, and, indeed, this is the most popular idea.  But before dismissing sexual selection, consider the behavior called ‘necking’, displayed by two male giraffes in the following clip.

It is evident that serious, and violent, combat occurs between males, and Simmons and Scheepers record several accounts of serious injury and death resulting from necking. Mitchell and colleagues, nonetheless, conclude that sexual selection is not the cause of long necks:

Support for this theory [the sexual selection hypothesis] would be that males invest more in neck and head growth than do females. We have investigated this hypothesis in 17 male and 21 female giraffes with body masses ranging from juvenile to mature animals, by measuring head mass, neck mass, neck and leg length and the neck length to leg length ratio. We found no significant differences in any of these dimensions between males and females of the same mass, although mature males, whose body mass is significantly (50%) greater than that of mature females, do have significantly heavier (but not longer) necks and heavier heads than mature females. We conclude that morphological differences between males and females are minimal, that differences that do exist can be accounted for by the larger final mass of males and that sexual selection is not the origin of a long neck in giraffes.

Mitchell et al. also dispute the importance of predation on giraffes, which Simmons and Scheepers thought was higher on males as a consequence of the physiological and anatomical costs of such an outsized structure.  Many people might think, What could catch and kill a giraffe? The answer: lions. In the following clip, an adult giraffe is killed by a group of lions.

4 Comments

  1. Reginald Selkirk
    Posted May 18, 2009 at 6:54 am | Permalink

    “First Ever: Lion KILLS Giraffe”

    Meh. Now, when a giraffe kills a lion, let me know.

  2. Jeremy
    Posted May 18, 2009 at 10:41 am | Permalink

    I presume you’ve all seen the famous Battle at Kruger (National Park) – http://www.youtube.com/watch?v=LU8DDYz68kM

    It’s amateur footage, but it’s won all sorts of awards, and was recently bought by National Geographic.

  3. araujo
    Posted May 18, 2009 at 5:52 pm | Permalink

    I think the best explanation is still the one at:
    CAMERON, E. & TOIT, J. T. du. Winning by a neck: tall giraffes avoid competing with shorter browsers. American Naturalist, 169: 130-5, jan. 2007.

  4. David
    Posted May 19, 2009 at 5:13 pm | Permalink

    That take down of the giraffe seemed awfully easy, even for lions, so I wondered what the deal was a did a little digging. It turns out the giraffes have a disadvantage walking on the roads so the lions have learned to force them out there.

    Looking at that road and woods, without the big game you could have convinced me that lions video was somewhere up at Kettle Moraine (and they’ve been starting to see wolves up there, so who knows…)


2 Trackbacks/Pingbacks

  1. […] found this clip from a post on the Why Evolution is True blog. Two male giraffes fight by doing what’s called “necking” (it isn’t sweet). […]

  2. […] a previous post, on how giraffes got their long necks, I noted that this was a venerable question in biology. The […]

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