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Re: How The Giraffe Got (or didn't get) Its Long Neck



In that pace we will go back to "lamarckism".

What about okapi? No useful information from comparative anatomy and embryology?

And what about fossils? Are there more or less compleat fossil
skeletons from ancient Giraffidae?

[]s,

Roberto Takata

On Tue, May 19, 2009 at 1:49 AM, Richard W. Travsky <rtravsky@uwyo.edu> wrote:
>
> with maybe some relation to long necked dinosaurs...
>
> http://news.bbc.co.uk/earth/hi/earth_news/newsid_8050000/8050298.stm
>
> For centuries experts have argued over how the giraffe got its long neck.
>
> Some said it helped the giraffe feed on leaves other animals cannot, while
> some suggested it evolved as a consequence of giraffes evolving long legs.
>
> But evidence for such ideas remains flimsy. Now one of the more recent
> hypotheses has also bitten the dust.
>
> Giraffes did not grow elaborately long necks as a sexual signal, scientists
> have shown, leaving its origins a mystery.
>
> In the journal Zoology, Professor Graham Mitchell of the University of
> Wyoming, in Laramie, US, and colleagues Professor John Skinner and Dr S J
> van Sittert of the University of Pretoria in South Africa report that there
> is still no consensus on the origin of the giraffe's neck.
>
> The theory which most support, they say, is that the neck confers a feeding
> advantage, allowing the giraffe to reach leaves beyond more numerous smaller
> browsers such as gazelles or antelope.
> [...]
> More recently, another popular idea emerged: that sexual selection, rather
> than natural selection, drove the evolution of the giraffe's neck.
>
> The idea is that down the generations, males evolved ever longer necks to
> dominate rivals for the affections of female giraffes. The fact the male
> giraffes uniquely wrestle for dominance by "necking" and "head clubbing" one
> another, with males with the longest necks and heaviest heads tending to
> win, has been forwarded as evidence to support the hypothesis.
>
> So Professor Mitchell and his colleagues decided to put the sexual selection
> hypothesis to the test by examining 17 male and 21 female giraffes.
>
> If long necks were a sexually selected trait, they expected to find a number
> of things:
>
>    * Long necks should be more exaggerated in males than females
>    * They should evolve to be bigger in size more than other parts of a
> giraffe's body
>    * They should confer no immediate benefit to survival, and may come at a
> cost
>
> Their results didn't support any of these propositions.
>
> They could find no significant differences in the relative size of male or
> female necks. [...]
> But they can say that any advantages that were gained don't appear to have
> been sexual in nature. "Better explanations for neck elongation must be
> sought elsewhere," they write.
>