Showing posts with label form. Show all posts
Showing posts with label form. Show all posts
Monday, January 3, 2011
What is a cockroach?
This is a cockroach, order Blattodea. Insects in the order Blattodea (or Blattaria if you're old-school - either way it's a roach) are characterized by long, slender cursorial (running) legs with which they achieve impressive speeds. The top of their first thoracic segment (aka the pronotum) extends up to cover their heads as a shield-shaped hat. Their mouths contain a pair of plain, sensible mandibles for chewing, their 30+ segmented antennae are thin and sensitive, ranging far ahead of their body to warn of impending danger as they run. In those cockroaches that have wings, the first pair is thickened, leathery (they're called tegmina), protecting the hind pair that is thin and membranous.
Many cockroaches are earth-toned: dull brown, tan, red, and black. A few, like the beautiful cuban cockroach (Panchlora nivea) pictured above, have striking coloration.
One thing a cockroach is not, however, is fancy. You will never find them trying to stand out with flashy patterns. They are meant to blend in with the background. Flat bodies, shielded heads, leathery forewings, the body of a cockroach is made for sneaking into small hiding places and for furtive avoidance of malicious predators. Their beauty is a functional one.
Thursday, September 23, 2010
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.
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.
Tuesday, September 21, 2010
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.
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.
Antennation
Insect antennae are sophisticated organs that can perform many functions for insects:
Basically, antennae can do everything but see. They play powerfully in orientation of the insect in space; detecting wind speed and direction, the smell of pheromones in the air leading them to a mate, or the subtle vibration of prey below the bark of a tree. What is interesting to me is that antennae have so many different forms. Termites have simple moniliform antennae like tiny strings of tiny beads. Silkmoth and mosquito males have elaborate bipectinate plumose antennae. My small hive beetles have adorable club-shaped antennae which make them look like Mickey Mouse when they hold their antennae up. The antennae of house flies are two fat dangly bulbs with a single feather mounted at the top of each. The antennae of scarab beetles terminate in a fan-like array of delicate fingers called lamellae that can be spread open or closed tightly like a fist and tucked away into cavities under the insect's head. Dragonflies have nothing but two short bristles for antennae. Dizzying variety is the rule when it comes to antennal form. So why so many types? Does each of them correspond to some special life-style like insect leg types?
Question of the day:
Dunno.
No, seriously- we don't know why there are so many types of insect antennae. Generally, where olfaction is important, we find more elaborate or specialized antennae, such as those of male moths. Dragonflies, on the other hand, hunt primarily by sight, and thus may be forgiven for having simple and uninteresting antennae. Evolution seems to have favored divergence in most cases and convergence in a few like the elbowed antennae of weevils and ants. Beyond that, antennae are as diverse as the insects themselves. Family resemblance in the antennae is quite useful for classifying insects, but why scarab beetles have fancy lamellate fingers and small hive beetles small club-shaped antennae is rather a mystery.
Some questions in biology will always be easier to answer with "It's for decoration" or "Because that's how God made him." And perhaps in a sense, this is true- that God has seen fit to elevate diversity over uniformity, and style sometimes seems to trump function. But as we scientists study and search for a function for strange traits and find that they do, indeed, have a function, are we disappointed? On the contrary, when fascinating form and amazing function come together we get a new sort of joy- beyond the joy of beauty and the joy of a well-made machine. It is the joy of something that is, on all accounts, very good - just as the creator said it was.
- Olfaction (smell)
- Gustation (taste)
- Mechanoreception (feeling)
- Hygroreception (humidity detection)
- Thermoreception (temperature)
Basically, antennae can do everything but see. They play powerfully in orientation of the insect in space; detecting wind speed and direction, the smell of pheromones in the air leading them to a mate, or the subtle vibration of prey below the bark of a tree. What is interesting to me is that antennae have so many different forms. Termites have simple moniliform antennae like tiny strings of tiny beads. Silkmoth and mosquito males have elaborate bipectinate plumose antennae. My small hive beetles have adorable club-shaped antennae which make them look like Mickey Mouse when they hold their antennae up. The antennae of house flies are two fat dangly bulbs with a single feather mounted at the top of each. The antennae of scarab beetles terminate in a fan-like array of delicate fingers called lamellae that can be spread open or closed tightly like a fist and tucked away into cavities under the insect's head. Dragonflies have nothing but two short bristles for antennae. Dizzying variety is the rule when it comes to antennal form. So why so many types? Does each of them correspond to some special life-style like insect leg types?
Question of the day:
Why are there so many types of insect antennae?
Answer:
Dunno.
No, seriously- we don't know why there are so many types of insect antennae. Generally, where olfaction is important, we find more elaborate or specialized antennae, such as those of male moths. Dragonflies, on the other hand, hunt primarily by sight, and thus may be forgiven for having simple and uninteresting antennae. Evolution seems to have favored divergence in most cases and convergence in a few like the elbowed antennae of weevils and ants. Beyond that, antennae are as diverse as the insects themselves. Family resemblance in the antennae is quite useful for classifying insects, but why scarab beetles have fancy lamellate fingers and small hive beetles small club-shaped antennae is rather a mystery.
Some questions in biology will always be easier to answer with "It's for decoration" or "Because that's how God made him." And perhaps in a sense, this is true- that God has seen fit to elevate diversity over uniformity, and style sometimes seems to trump function. But as we scientists study and search for a function for strange traits and find that they do, indeed, have a function, are we disappointed? On the contrary, when fascinating form and amazing function come together we get a new sort of joy- beyond the joy of beauty and the joy of a well-made machine. It is the joy of something that is, on all accounts, very good - just as the creator said it was.
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