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Posted - 03/12/2004 :  21:47:38  Show Profile Send moolmogo a Private Message
i heard something about natural selection. it was something about giraffes and other animals that live in the same environment. why did the giraffes have to grow long necks when there are animals with short necks surviving fine in the same environment? and also about horses and cows. something about the horses crown teeth.

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Posted - 03/12/2004 :  22:06:17   [Permalink]  Show Profile  Visit gezzam's Homepage Send gezzam a Private Message

Tree leaves that are high above the ground represent a food resource. Mammalian species have utilized a variety of adaptations to take advantage of this resource. Koalas and sloths climb the trees to get the leaves. Elephants may use their trunk to pull down tree limbs. Giraffes have an elongated neck and a specialized tongue.

The okapi is an extant relative of the giraffe. As a browser, it utilizes food resources both near the ground and on shrubs or trees. It also has a long tongue which is used to collect leaves from tree branches.

The giraffe is simply a specialist browser utilizing a food resource for which it need not compete with many other browsing or grazing species. The route to specialization is not discontinuous, as the example of the okapi shows.

Cut and pasted because I am a lazy bastard and can't be bothered typing...

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Dave W.
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Posted - 03/12/2004 :  23:10:48   [Permalink]  Show Profile  Visit Dave W.'s Homepage Send Dave W. a Private Message
moolmogo wrote:
why did the giraffes have to grow long necks when there are animals with short necks surviving fine in the same environment?
To add to what Gezzam cut-and-pasted, giraffes didn't have to grow long necks, their ancestor species happened to grow longer necks, and it seems to have given them some advantages.

I can't find anything on cows, horses, and a comparison of molars. And if I'm reading this diagram correctly, I'm not surprised at the lack of comparative dentistry. It appears to say that the last common ancestor (LCA) of horses and cows existed some 83 million years ago (compare with 5-6 million for the LCA of humans and chimps), and that horses are more closely related to cats (LCA at 74 million years ago) than they are to cows.

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SFN Regular

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Posted - 03/15/2004 :  13:33:25   [Permalink]  Show Profile Send furshur a Private Message
it was something about giraffes and other animals that live in the same environment. why did the giraffes have to grow long necks when there are animals with short necks surviving fine in the same environment?

First, the short necked animals are grazers, that is they eat grass. The taller and longer necked animals are browsers, that is they eat buds and leaves of trees and shrubs. These longer limbs and neck are even seen in browsing gazells. So browsers and grazers utilize different foods and therefore have different body types.
Second, any population of an animals species has a range of sizes. Such as humans, there are basketball players and there are jockeys. I can quite easily envision a periodic drought situation where the easy to reach browse is stripped away so that only the longer necked individuals survive. If this happens periodically the genes of the shorter necked animals are removed from the gene pool and replaced with only the longer necked genes. This will drive the population towards a long necked race. This has nothing to do with the giraffes 'wanting' a longer neck or stretching their necks. This also has nothing to do with an intellegint design it only has to do with the variability of the weather driving natural selection.

Evidence for evolution can be seen in a giraffe in particular for another reason. If I was going to design a giraffe I would certainly put more vertebra in it's neck than say a buffalo. I would have its neck have many vertebra like a dinosaur. The funny thing is a giraffe has the same number of vertebra as a gazelle or a buffalo. That indicates to me that it is just an adaptation that arose out of the existing gene pool of the proto-giraffe.

If I knew then what I know now then I would know more now than I know.
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