Troy Britain got blocked from the Institute for Creation Research facebook page because he criticized this comment:

Shouldn’t students be skeptical when they’re told that evolutionists can simply look at folds in embryos and see gill slits? The truth is that these are only folds of tissue in the pharynx region of vertebrates during the pharyngula stage of development. For mammals, birds, and reptiles, they never develop into a structure that is in any way like fish gills.

Britain has a good rebuttal in his article about “gill slits”, but I just have to point out something.

I’m an “evolutionist”. I don’t think any creationist would argue with that.

I teach students. Again, that’s indisputable — that’s my day job.

Furthermore, I teach relevant subjects: developmental biology and evolution.

But despite the fact that I ought to be example #1 for this terrible crime the creationist is condemning, I have never taught that all vertebrates have “gill slits”. I don’t know anyone who has. I took comparative anatomy and physiology in the 1970s, ages ago, and my instructors were all very explicit about the function, development, and evolution of pharyngeal structures. I would have been dinged badly if I’d made the mistake of suggesting that the pharynx was primitively a respiratory structure, rather than a feeding specialization.

It is quite correct that in most tetrapods, pharynx structures don’t form gills — gills are specialized derivatives of pharyngeal pouches, just as are hyoid arches and jaws. No one knowledgeable claims that humans develop fish-like gills. “Gill slits” is a colloquialism, not a technical term.

I am amused by the dismissal that they are “only folds of tissue”. Yeah, right. Your brain was only a fold of tissue in the pharyngula, too. Your major organs were mere diverticula. Your eyes were just outpocketings of the neural tube. Mere, just, only. Let’s all dismiss fundamental developmental structures as silly piles of cells, since, as we all know, mere cells do nothing, unless we’re trying to argue that they’re so darned complex that only a god could have created them.