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 #3: What your momma gave you

Existing genetic variation

Natural selection can only work on existing genetic variation. There is a gene pool, and out of it survivors are selected to reproduce for the next generation's gene pool, but no one who isn't already in the pool can be invited in.

In other words, on your birthday, your momma gave you some genes - dimples, a rear end the size of Milwaukee, maybe a mustache. Bummer- you really wanted rocket thrusters. But your momma could only give you genes that she already has, likewise your daddy couldn't pull rocket thrusters out of the air to give to you.

Some things, like rocket thrusters, would be totally sweet to have, but let's face it- you're not going to get them anytime soon. Fish might really wish that they had lungs in addition to gills, but they're not going to get them anytime soon. So it's foolish to ask "why don't fish have lungs?" or "why can't people fly?"

Adaptationism would cause us to answer these questions by looking for reasons why it wouldn't be advantageous to have rocket thrusters. But clearly, personal rocket-assisted flight would be advantageous. Going back to the insect antennae- we might expect that having foldable, elbowed antennae would be advantageous to any insect. But not everyone's got the genetic wherewithal to make elbowed antennae. The reason why a certain insect has a certain kind of antennae might not be related to what is most advantageous for that insect, but rather, what that insect's momma gave them.