The Clever Badger To add insult to injury, the platypus is leading.

Woodpeckers and Evolution – Part 1 (Edited)

A couple of weeks back, Miss Cellania wrote a Mental_Floss article describing the some of the weirdness to be found in birds.  One of the birds she mentioned was a particular species of woodpecker, that has a bizarre tongue.  She mentioned that this woodpecker has been used by both evolutionists¹ and creationists in support of their positions, and linked to an essay from each side.

I asked Miss C if she would mind if I used her article as a starting point for some analysis of the different perspectives on this bird, and she graciously agreed.  The reason I made a point of asking is that the evolution/creation issue is a hot-button topic, and I didn't want to drop Miss C into the middle of it, even by association. (Her article didn't take a strong position on the matter. Mine will.)

That preamble out of the way, let's look at woodpeckers.

Firstly, we're not worried about this guy:

Amusing, but not relevant

We'll be considering woodpeckers of the less slapstick variety, like this one:

Now we're talking

Specifically, we're going to be talking about the freakishly long tongue that certain woodpeckers have, and how it got to be what it is.  Miss C had a really good photo of our subject of discussion, which I've reproduced below:

Jenkies!

Now, before we proceed, we need to be familiar with a little piece of anatomy called the hyoid bone.  The hyoid bone serves as an anchor for the muscles of the tongue (among other things).  In people, it's small and U-shaped, and sits in your throat:

The human hyoid bone

It's an easily broken bone, and it's often fractured in strangulation victims.  (The next time you're watching NCIS, and Ducky turns to Gibbs and gravely intones "I can tell she was strangled, Jethro.  Her hyoid bone is fractured", this is what he's talking about.)

Birds have hyoid bones, too, but they're quite a bit different than those of humans.  A bird's hyoid is shaped like the letter Y, with the horns of the Y branching to either side of the throat and pointing toward the back of the skull  and the base of the Y actually extending into the bird's tongue.  (See Figure 2 in this article at talkorigins.org.)  Actually, a bird's hyoid looks somewhat like the threaders my kids' orthodontist gives them to floss their braces (the right end of the loop would be open, and at the back of the skull - we'll refer to that as the proximal end - and the single filament at the left would be interior to the bird's tongue - we'll refer to that as the distal end.):

Orthodontic floss threader

You may have noticed that I said (twice) that the bone goes into the bird's tongue.  Our tongues are basically all muscle.  A bird's tongue is more like a flesh covered bone spear.  The bone, by the way, is thin enough to be  flexible, which is important to keep in mind when we consider what actually happens when the bird extends its tongue.

Each one of the hyoid horns is surrounded by a sheath of tissue in which it can slide.  There are some muscles called the branchiomandibularis muscles which connect the proximal ends of the horns to the bird's jawbone.  When these muscles contract, they pull the ends of the horns forward, which moves the entire hyoid/tongue apparatus forward, tightening the hyoid horns against the skull, which in turn extends the tongue.  So, all other things being equal, longer hyoid horns paired up with correspondingly longer branchiomandibularis muscles enable the tongue to be extended farther m out of the beak.  It's worth noting here that juvenile woodpeckers have relatively modest hyoid horns, and the horns grow as the bird grows, and in species with the freakishly long tongues such as the one in Miss C's article, the process is no different.  The horns just grow longer and continue the typical march up the back of the skull, and happen to end up growing all the way around.

In the next entry, I'll work through Rusty Ryan's post at talkorigins and highlight the reasons why biologists aren't at all puzzled by the woodpecker's tongue and why conventional evolutionary explanations of it's development are perfectly sufficient to explain it.²

CB

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¹I don't like the term evolutionist. Henceforth, I'm going to use the more accurate term, biologist. Working biologists accept evolution. Period. I likewise don't like the term Darwinist, since it implies that the evidence for and knowledge of evolution circa 2009 hasn't changed a whit since Darwin published Origin in 1859. Darwin didn't know genetics. Genetics was a game changer for evolutionary theory, since it provided the physical mechanism for the processes that Darwin envisioned.

²A tactic that turns up repeatedly in creationist literature is to pick some odd feature of some organism, assert that the feature can't be explained by evolution (or, more dramatically, that the feature is an embarrassment that biologists don't want to address), and then declare that "since evolution can't explain" it, the creationist position must perforce be correct.  That simply isn't true, and in a sense it's just another manifestation of the fallacy of false choice that I talked about here.  But it has a bigger problem - it assumes that scientific knowledge doesn't grow.  It assumes that because biologists haven't figured out how some feature arose, they never will, and that's a very poor assumption.