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 #1: Founder Effects

This is the first in our series examining the limits of adaptationism, where we will examine why teleological questions (asking "what for?") don't necessarily get us the right answers in biology.

Take for example a man with an elaborate mustache. What is a mustache for? We could come up with all kinds of wild functional explanations for why mustaches exist, but none of them truly convincing. We know that men without mustaches live very normal, if not happier lives, than men with mustaches. In this era of human biology, mustaches are selected against, and the men who grow mustaches are cursed by the necessity of shaving them if they want women-folk to like them. In localized hipster populations, this trend can be reversed, but let's just say for the sake of argument, that all women feel more or less like I do.

So the reason for mustaches isn't really clear. Adaptationism would assert that since it takes energy to produce and maintain a sweet 'stache, it must serve some purpose for the adult male human, otherwise it would have been lost from the population and men would be largely mustache-less. But what if adaptationism has led us down a rabbit-trail looking for reasons where they may not exist?

An alternative explanation for why mustaches exist may be a genetic constraint on natural selection known as the founder effect or legacy effect. Basically, you can't throw out all your starting material and start over when starting a new population. The population always has founders. Perhaps the founders of the male human population had facial hair on their upper lip. Perhaps this was because they were bigfoot or wookie-like creatures with a lot of fur anyway. Selection against large amounts of body hair has occurred over the evolution of male humanity, but because of the founder effect, it's going to take a lot to get rid of those mustache genes.

Similarly, the legacy effect is a constraint placed on selection now due to selection in the past. A couple centuries ago, mustaches were the hotness. Women felt they were manly, and preferentially mated with men who had mustaches over those who did not. Now we have a gene pool full of mustaches, and we can't really get rid of them due to the legacy of the age of mustache-rage.

So, the "what for?" question doesn't help us understand what mustaches are for, unless we ask what mustaches might have been for back in the evolutionary history of hairy men.

If we go back to our insect antennae, we may ask why certain insect taxa seem to have a particular style of antenna. The question may not have a functional answer, because the reason for different styles of antennae is buried far back in the evolutionary history of these bugs. Perhaps the founders of modern butterflies had knobbed antennae, and the founders of modern moths straight or plumose (mustache-like) antennae. The reason why their antennae diverged back in that day may be as simple as genetic drift or it may have had a functional meaning in those days, but today it seems to be the capricious whim of a God who likes knobby antennae.

Photo by Flickr user a4gpa licensed for re-use by Creative Commons license.

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.