Jet-propulsion

In a previous post I talked about how totally awesome and totally impossible it would be to be born with rocket-thrusters. As personally disappointing as this is, I take joy in the fact that many other animals are blessed with magnificently bizarre methods of locomotion.

Dragonfly larvae, for example. They are rather ugly brown critters that swim around in shallow ponds, catching small invertebrates and fish with an extensible bear-trap jaw, biding their time until they can emerge as adult dragonflies and take up their rightful place among the high-speed insect jewels in the sky.

Dragonfly larvae do not have paddle-like appendages for swimming under the water. They are not helpless, however, against predators. God, in his wisdom, has given them jet-propulsion. When chased, a dragonfly larva will suck water into its anus like a turkey-baster and then blast it out, propelling itself through the water with surprising speed. Yes, dragonfly larvae are equipped with their very own rectal rocket-thrusters.

If that wasn't awesome enough for you, the gills of dragonfly larvae are also housed within the rectum. Picture, for a moment, what a different life it would be to use your rectum for both jet-propulsion and breathing.

And now you know why I feel my heart rise into my throat when I study insects. There is something ludicrous everywhere you look.

Limits of adaptationism

Yesterday we talked about the "why" of insect antennae. Why ask why?

When biologists ask "why" - they are usually asking for a functional "because." The question could be re-phrased as "what for?" This is a very old approach for understanding how biological things work. It assumes that there's a certain order to things, that organisms are a certain way for a reason. God, in his infinite wisdom, made them that way to be suited to their world.

William Paley talks a lot about this. He's the guy who came up with the watchmaker argument for the existence of God. This argument basically states that a watch is complex and contains a mechanism that works in a intricate way to keep time, so when we see a watch, we get a sense that it has purpose and design and therefore a designer. Living things like animals and plants are likewise complex and work in an intricate way to perform their tasks of survival and reproduction. Ergo, living things have design and have a designer. And it follows that the traits expressed by these living things should have a purpose in that design.

But what about traits of living things that seem to have no function? Are they just fanciful inventions of a whimsical God? Whimsy is not something I typically attribute to God. So perhaps there are other explanations. For the next several days we'll examine the limits of adaptationism - why we cannot always ask why and get a straight answer in biology.