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



The article is open access and can be found here:

 http://www3.interscience.wiley.com/cgi-bin/fulltext/122328715/PDFSTART

-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of
Richard W. Travsky
Sent: Monday, May 18, 2009 11:50 PM
To: dinosaur@usc.edu
Subject: How The Giraffe Got (or didn't get) Its Long Neck


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.