Posted by: Ticktock | April 21, 2009

Investigating Giraffe Evolution!

I visited Cincinnati’s zoo with little Juliet a few days ago.  It’s one of the oldest zoos in America, but they continue to expand and improve the animal habitats.  One of the new features is a feeding deck for the giraffes.  As I was watching the exotic creatures snake out their tongues for some tasty straw, I overheard a man talking to his wife about evolution.

“I totally understand evolution for some animals, but giraffes have me perplexed.”

I thought about it and decided that the matter needed investigating.  I’ll never see this man again, but he left me with an itch that I had to scratch.  How did giraffes evolve?  Where did those long necks come from?  What is the deal?

It turns out that giraffe evolution is not an open and shut case.  Creationists have been trotting out arguments about how there are gaps in the fossil record.  They also claim that the long necks co-evolved elaborate biological functions, which, in their minds, must be impossible.

Darwin actually handled the latter argument quite well in his own published writings.

With animals such as the giraffe, of which the whole structure is admirably co-ordinated for certain purposes, it has been supposed that all the parts must have been simultaneously modified; and it has been argued that, on the principle of natural selection, this is scarcely possible. But in thus arguing, it has been tacitly assumed that the variations must have been abrupt and great…

Most of the “special” biological features that make a giraffe’s neck possible are just adaptations of traits shared by all mammals.  There’s no reason that these traits couldn’t have co-evolved slowly; as the neck lengthened, the valves and arteries were naturally selected as well.   See more about this at SkepticWiki!

Creationists exaggerate missing gaps in the fossil record to poke holes in Darwinian evolution, but the argument is a fallacy called “god of the gaps” .  Since there are unexplained gaps in the fossil record, creationists believe that god must be the default answer.  The chance that such a transitional fossil may yet be found does not seem to be an acceptable option to creationists.  It’s ironic that gaps in the fossil record are held up by creationists as proof against evolution because some of evolution’s greatest victories have come from the discovery of missing links.  Gaps in the fossil record have allowed scientists to make predictions on the types of fossils they expect to find (such as a transition between fish and amphibian – tiktaalik).  The sign of a good theory is one that scientists can use to make verifiable predictions.

Intelligent design advocates have tried the “god of the gaps” tactic with whale fossils, but they’ve been repeatedly beaten down by the discovery of numerous transitional whale fossils that fill the gaps between ambulocetus and the modern whales.

It’s true that the known fossil record has always lacked an extensive library of transitional giraffe fossils, but just because there aren’t as many known giraffe ancestors as horse ancestors doesn’t mean that giraffes are exempt from evolution.  It shouldn’t be too much of a leap in logic for creationists to imagine the transitions between the deer-sized giraffe ancestor climacoceras and the modern giraffe. Indeed, if one looks at the current collection of transitional giraffe species, the gaps don’t seem too vast, actually:  climacoceras, Palaeotragus, samotherium, honanotherium, etc. Evolution’s proven track record allows me the safety of predicting that there will be even more giraffe transitional fossils discovered.

So, how and why did Giraffes get those long necks.  Why did the oft overlooked Giraffe sibling species, the okapi, not receive such exotic traits.

The initial default answer given by Darwin and Lamarck, and most zoo visitors like myself, seems to be the idea that long necks were an advantage for giraffes when they needed to eat leaves from tall trees during the summer drought.  This hypothesis has been criticized for various reason.

The prevailing theory is that the long necks are sexually selected by the females.  This sexual selection can be seen when the male giraffes start slapping each other around with their massive necks until the winner eventually mounts the damsel in heat [gross aside: male giraffes know a female is in heat by tasting her urine].

There are other theories too.  Some say that the long legs make it easier for giraffes to run away from most predators.  Others say that the long necks make it easier for giraffes to see approaching predators.  I don’t see why both of these observations can’t be additional valid explanations of natural selection, along with the sexual selection theory favored by biologists.

I don’t blame the guy at the zoo for being baffled by giraffe evolution.  The explorers who originally rediscovered giraffes called them camelopards (now Giraffa camelopardalis) because they resembled a cross between a camel and a leopard.  I may not have found Kirk Cameron’s fabled “crockaduck”, but I did learn a few neat things about the giraffe, and it’s ancestors.  Sometimes it’s fun to follow up on a random comment.  I always wind up learning something new.

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Responses

  1. I’m planning to take my kids to the Atlanta zoo this week. Now I will have something to interesting to tell them.

  2. You might find this article of interest: “Unintelligent Design,” by Jim Holt, in the NY Times Sunday Magazine, February 20, 2005. It includes this factoid:

    But if we can’t infer anything about the design from the designer, maybe we can go the other way. What can we tell about the designer from the design? While there is much that is marvelous in nature, there is also much that is flawed, sloppy and downright bizarre. Some nonfunctional oddities, like the peacock’s tail or the human male’s nipples, might be attributed to a sense of whimsy on the part of the designer. Others just seem grossly inefficient. In mammals, for instance, the recurrent laryngeal nerve does not go directly from the cranium to the larynx, the way any competent engineer would have arranged it. Instead, it extends down the neck to the chest, loops around a lung ligament and then runs back up the neck to the larynx. In a giraffe, that means a 20-foot length of nerve where 1 foot would have done. If this is evidence of design, it would seem to be of the unintelligent variety.

    • Holt’s paragraph in the NY Times, referenced above, is better stated, and has been stated countless times by countless folks as;
      There is no intelligent design, Creator, or God, because if there were, this designer would have done things just as I perceive they should be done. It is impossible for a Creator to disagree with my great intellect, therefor there is no Creator.

      • Nope. It’s this: The giraffe uses a 20-foot length of nerve because the nerve was in place when the long neck began to evolve, so that the nerve naturally lengthened.

        No need to involve a God or Creator or Intelligent Designer at all. Note Occam’s Razor: evolution (which we can actually observe happening) is sufficient to explain what we observe. Dragging in an invisible and all-powerful omniscient God is an unnecessary (and logically self-contradictory) proposition.

        For more on the logical self-contradiction, see Charles Hartshorne’s fascinating book Omnipotence and Other Theological Mistakes.

        BTW, the word “therefore” ends with an “e”.

        Have a nice day.

  3. Hmm very interesting, good find! That IS one of the few animals where you go what the hell made you this way?

  4. You missed the point of my post. The point wasn’t creation/evolution, or giraffes, but the fallacy of Holt’s premise.(my intelligence can’t comprehend the reasoning, therefore the reasoning can’t be from an intelligent source, it is impossible for there to be intelligence beyond my capability to understand). As far as the creation/evolution debate, I’m glad to leave that to another forum, but that argument, as all arguments, when engaged, should be done so with sound logic, not fallacy.

    BTW, thank you for the spelling corection!!

  5. I didn’t know the giraffe had this many known ancestors. Thanks for the information.


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