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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".<<<
Huh? You can derive elongate necks that aid in feeding with a
Darwinian selective regime. Just because people use the case of
giraffe necks to contrast Darwinian selection with Lamarckian change
(or rather a caricature thereof) doesn't imply that both can't be used
to explain it (note, I am not endorsing Lamarck's ideas, merely
agreeing with S.J. Gould that the textbook description of his idea is a
caricature of the position Lamarck actually held).
And what about fossils? Are there more or less compleat fossil
skeletons from ancient Giraffidae?<<<
Yes, there are several species of fossil giraffid, some with long necks
and they didn't all live in Africa. That's something that people seem
to overlook when trying to explain giraffe necks, as nearly every
discussion I've seen presumes the modern African setting is the one
that lead to the evolution of their long necks, but of course this may
not be true. It could be that in other environments with different
feeding regimes, or even in the current one but when competing against
now-extinct herbivores that the long neck conferred a greater advantage
than it does now. It's also worth noting that an adaptation can be
more or less neutral most of the time but play a key role during times
of stress (eating above other herbivores might be _very_ advantageous
during times of drought, for example) and if=2
0those periods of selective
pressure are common enough then they will still drive phenotypic
change, even if during the majority of the animals life that selective
pressure isn't acting. And while I think the current study is correct
that sexual selection wasn't the driving factor, it could well be a
maintaining selective pressure, as mate selection often favors (and
therefore serves to reinforce) characters that have traditionally
played an adaptive role.
I don't know enough about giraffid biogeography off hand, but
personally my first inclination would be to look for the likely origin
of long-necked species and see what THAT environment was like before
attempting to speculate on what factor(s) drove the evolution of neck
elongation. Most current discussions (even in technical papers) ignore
the phylogenetic and temporal context that giraffes evolved in when
trying to solve this mystery.
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333
From: Roberto Takata <firstname.lastname@example.org>
Sent: Tue, 19 May 2009 11:06 am
Subject: Re: How The Giraffe Got (or didn't get) Its Long Neck
What about okapi? No useful information from comparative anatomy and
On Tue, May 19, 2009 at 1:49 AM, Richard W. Travsky <email@example.com>
with maybe some relation to long necked dinosaurs...
For centuries experts have argued over how the giraffe got its long
Some said it helped the giraffe feed on leaves other animals cannot,
some suggested it evolved as a consequence of giraffes evolving long
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,
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
van Sittert of the University of Pretoria in South Africa report that
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
advantage, allowing the giraffe to reach leaves beyond more numerous
browsers such as gazelles or antelope.rather
More recently, another popular idea emerged: that sexual selection,
than natural selection, drove the evolution of the giraffe's neck.
The idea is that down the generations, males evolved ever longer
dominate rivals for the affections of female giraffes. The fact the
giraffes uniquely wrestle for dominance by "necking" and "head
another, with males with the longest necks and heaviest heads tending
win, has been forwarded as evidence to support the hypothesis.
So Professor Mitchell and his colleagues decided to put the sexual
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
Â Â* Long necks should be more exaggerated in males than females
Â Â* They should evolve to be bigger in size more than other parts of
giraffe's bodycome at a
Â Â* They should confer no immediate benefit to survival, and may
Their results didn't support any of these propositions.
They could find no significant differences in the relative size of
female necks. [...]have
But they can say that any advantages that were gained don't appear to
been sexual in nature. "Better explanations for neck elongation must
sought elsewhere," they write.