You can hardly attend high school or college now days with out hearing or reading this "whopper". In fact[sic], neither gills nor their slits are found at any stage in the embryological development of any mammal including man. The folds in the neck[sic] region of the mammalian embryo, that are erroneously called "gills", are not gills in any sense of the word and never have anything to do with breathing. They are merely flexion folds, or wrinkles, in the neck[sic] region resulting from the sharply down turned head and protruding heart of the developing embryo. These folds eventually develop into a portion of the face, inner ear, tonsils, parathyroid and thymus. No reputable medical embryology text claims that there are "gill slits" in mammals.
Still, the gill slit myth[sic] is perpetuated in many high school and college biology text books as "scientific evidence" for evolution. Even Dr. Spock in his book 'Baby and Child Care' claims that "as the baby lies in the amniotic fluid of the womb, he has gills like a fish." Perhaps the "gill slit" myth[sic] continues to be taught because there is no better "evidence" for evolution. How many of you were taught the gill slit myth[sic] in school??
From: Stan Friesen
To: All Msg #111, Feb-17-93 02:46PM
Subject: Re: Gill Slits
Organization: NCR Teradata Database Business Unit
From: email@example.com (Stan Friesen)
In article <1993Feb12.firstname.lastname@example.org>, email@example.com (Robert Derrick) writes:
|> And that is, they are not gill
|> slits at all, and they share nothing in common with gill slits other
|> than a vague similarity of appearance, and in fact, they are nothing
|> more than folds of skin. ...
|> Are they really gill slits? Is there enough morphological/genetic/
|> etc. information to say what they are with certainty?
Well, they are identical in form in embryonic fish and embryonic tetrapods (land vertebrates) - they form at the same stage, they occur in the same *numbers*, they are associated with the same internal anatomical features, and with the same relationships to other organ primordia. And in fish they develope *directly* into the adult gills, with very little change other than elaboration of structure.
They are *certainly* more than just 'folds of skin'. Let us take just one of those associated features I mentioned - the blood vessels. In embryonic tetrapods the earliest form of the circulatory system includes a series of arched vessels leaving the heart and passing through the bars between the gill slits (called, naturally, the gill bars). Since there are always six gill slits (except in agnathans and some sharks), there are six aortic arches (as they are called) on *each* *side*. In mammals all but two of these arches subsequently disappear. One becomes the aorta, and the other becomes part of the one brachial artery. In birds a similar thing happens, except that the aorta is on the *other* *side*! So, not only do we have the formation of twelve holes that all eventually disappear, we have the formation of 10 arteries which also disappear. [In fish the aortic arches *all* remain, and provide blood to the gills for oxygenation].
Similar statements could be made about the innervation of the embryonic gill slits, their incipient musculature, and so on.
Now, you tell me, are thse gill slits or not?
I say, if it walks like a duck ...
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