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fetus with gill

Human Anatomy, Physiology, and Medicine. Anything human!

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Postby Jedi of Zen » Fri Apr 21, 2006 3:17 am

I agree with Melychath. To say that there's no need to search for a formative cause seems pretty flabbergasting to me. When someone from the conventional Darwinian camp is asked about the origin of life, their response typically amounts to something along the lines of a shrug and a "Meh...that's not really that important."

We live in a culture in which the word "God" tends to evoke a strictly fundamentalist Christian entity. It would be interesting if we could start thinking about "God" in terms of a formative cause, rather than a human-like deity.
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Postby AstusAleator » Fri Apr 21, 2006 9:04 am

Here's a pretty neat animation highlighting the neural chord of a human embryo that's about 32 days old. The rest of the site is pretty neat too. check it out.

About the CreationAnswers reference: This is a classic straw-man argument. They're taking a somewhat outdated hypothesis (vestigial organs) and treating it as the primary argument. If you can change the nature of your opponent, it becomes easier to defeat.
TOE simply hypothesizes that all chordates evolved from a common ancestor, because they share traits. In fact, these traits can be found in all chordates. In some, such as humans, some of the traits are only seen in embryologic stages.
This is a very basic step in cladistics, further proof is in more detailed analyses of other more intricate details.

Urochordates Image
and Cephalochordates Image
Are thought to represent what those common ancestors may have been like. Notice that the urochordates undergo a morphological shift during their development. A similar evolutionary shift is thought to have occured in chordate-ancestors.

Now focus on the main things that classify chordates (lets see if I can remember them all).
1. notochord or spinal column (ie vertebra)
2. pharyngeal (gill) slits
3. Postanal tail


Humans obviously have vertebrae. Do you see a neural extension beyond what will be the anus in the picture above (note: the neural channel is highlighted in the first link I gave)? Admittedly, the pharyngeal structures are much harder to see. Here's a picture in which you can see them a little more clearly.
Evolutionists hypothesize that pharyngeal gill arches may have been the precursers to such structures as the jaw bone and ear. It is, however, no surprise that out of the 3 traits, the pharyngeal slits are the least observable in most modern land-mammals. This could be due to the amount of time land-mammals have been evolving with no need for gills.

Does any of this prove evolution? No. Nor does debunking or attacking it disprove evolution. The above are just simple biological traits used to classify organisms and arrange them sensibly.

To address the original question: No, they're not gills. Gills are used for respiration. Their evolutionary lineage can likely be traced back to gills, more specifically pharyngeal arches. Read up a little on the origins of chordates and early fish; I promise you'll be fascinated.

All pictures above are from embryo.soad.umich.edu .
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Postby kiekyon » Fri Apr 21, 2006 9:36 am


i'll have to reread this :?
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