Are the “gill slits” of vertebrate embryos a hoax?

June 14, 2012 • 8:59 am

As most of us know (and all of us who have read WEIT), all vertebrate embryos develop “branchial clefts” (also called “pharyngeal arches” or “branchial arches”) at an early stage, and these are almost certainly the vestigial remnants of the clefts of our fishy ancestors, which develop into gills. Those branchial clefts are sometimes called “gill arches,” even in species, like reptiles, bird, and mammals, that never have gills.  In humans, for example, the clefts disappear and transform into other parts of the body, including the jaw, the middle ear, and the larynx.  Here’s a photo from Wikipedia showing them in humans:

And here they are in a cartilaginous “fish,” a skate (yes, some will take issue with that name, but it’s irrelevant for our purposes):

The second photo is taken from a wonderful new post on the weirdly-named website Playing Chess with Pigeons, written by Troy Britain. The post is called “Gill slits by any other name,” and it’s not only an explanation of where these things come from and what they become in vertebrates, but also an eloquent attack on creationist (and intelligent-design) claims that these “gill slits” in non-fishy vertebrates have nothing at all to do with evolution (here’s an example of one such attack on my book).

The creationist/ID attack on “gill slits” in amniotes (basically, mammals, birds, and reptiles) goes as follows (this is from Britain’s post).

  1. Pharyngeal structures of amniote embryos never function as gills and therefore should not be referred to as “gill slits”.
  2.  Whatever resemblance to the gills of aquatic vertebrates the pharyngeal structures of amniotes has, it is superficial.
  3. Seeing the pharyngeal structures of amniote embryos as being gill-like and calling them gill-slits despite their not functioning as gills is “reading evolution into development”.

Britain takes these claims completely apart.  Go read his post: it’s long but really educational and accessible to everyone.  If you want to spend half an hour learning some great evolutionary biology, by all means invest it in reading Britain’s discussion.

32 thoughts on “Are the “gill slits” of vertebrate embryos a hoax?

  1. Whew! For a moment there I was afraid we’d have to change the song lyrics.

    Actually, I’d already read Troy Britain’s post on gill slits and his outstanding takedown of creationist idiocies. It made me a regular at his website.

  2. Have to recommend Your Inner Fish by Neil Shubin … seem to remember there is a lot on this topic and it was really well written and interesting!

    1. I’ll second that. The book managed to be relatively brief and to the point, interesting, engaging and just a damn good story.

  3. Thanks for this post. BTW, a look at what JAC calls Britain’s “weirdly named website” (Playing Chess With Pigeons) reveals that he took the name from a remark by one Scott Weitzenhoffer’s: “Debating creationists on thetopic of evolutiton is rather like trying to play cheess with a pigeon; it knowck s the pieces over, craps on the board, and flies back to its flock to claim victory.”

      1. Dangit, you beat me to the punch on the Chess with Pigeons moniker. I just LOVE that visual analogy!!

        1. But my first place medal 😉 should be confiscated and the honor 😉 passed to you, since if I’d stopped to notice and correct my typos like a good commenter should, you would have probably gotten in there first.

    1. Hadn’t heard that chess/pigeon comparison before. Absolutely wonderful! It’s so apt and such a great visual. LOL

  4. Thanks for making my day!

    Troy Britain’s exposition is delightful.
    I hated the dreadful embryology course in my student days, thirty-odd years ago, (all in German, with the quaint terminology of Kiemenbogen/Kiemenfalten, Schlundbogen/Schlundfalten etc. and all the references to Haeckel, Rathke, Wagner & tutti quanti, but I see now it was not entirely lost. The puzzle pieces are falling into place. At last.

  5. Look, a LOLcreationist!

    Pharyngeal structures of amniote embryos never function as gills and therefore should not be referred to as “gill slits”.

    Brain structures of creationist embryos will never function as independently thinking and therefore should not be referred to as “brains”.

    1. I don’t usually go for the controversial, but could one suggest as well that embryos which never function as people shouldn’t be called “a person”?

    2. While reading, I was thinking something similar; Structured gods of christian mythology never function as God and therefore should not be referred to as God.

      Zombie Jesus, what do you want for christ’s birthday?

      Brains! Brains! Always Brains!

  6. Aw, y’all, you’re being too hard on these creationaries. For whatever reason, they’re not able to go to college and so they spread lies so some biologist will take the time to give them a free lecture.

    That of course doesn’t apply to the loathsome Jonathan Wells (as quoted at Playing Chess), who knows full well what a superficial argument he spins (you don’t get into Berkeley by being that fucking stupid).

    1. Unfortunately, far too many of them go to college. The worst end up with degrees in education. Their science background consists of a year spent flinging bible quotes in geology class.

  7. Oh, small world syndrome! I used to batter Creationists on Compuserve with Troy. Well, with someone answering to “Troy Britain”. It’s unlikely, but not impossible that we’ve got an example of convergent taxonomy, but I’ll pop over and see how he’s doing. Evidently still fighting the Good Fight.

    1. Must be the same guy. And a masterful demolition of the Creationist objections to this datum of common descent. I often wished that I could devote the time and attention to detail that Troy does, but I can’t, so I don’t.

  8. here they are in a cartilaginous “fish,” a skate (yes, some will take issue with that name, but it’s irrelevant for our purposes):

    I see nothing wrong with calling a skate a skate.

    There’s nothing wrong with calling it a “fish” either, even without the Quotation Marks of Paraphyly, as long as we’re talking English and not Bioscientificalese.

  9. What’s the story behind the skates? Skates and rays look like fish to me – they’re just flattened the other way.

    I wonder why it was called a ‘pharyngula’ stage; with the nose being so prominent I would have expected it to be called the ‘Tongilianus’ stage.

  10. Just a thought, and I have no scientific background so please be gentle with me! Would it be possible to manipulate a mammal embryo so that the gills actually formed? The mouse from Atlantis would take some explaining away.

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