Bible Humper

Hello there. A Christian friend of mine believes that evolution is guided by God and could not work without his "guidance". <img src="graemlins/banghead.gif" border="0" alt="[Bang Head]" />

I could use a hand please.

Basically what it came down to was that while "survival of the fittest" is adequate to explain why animals would get smarter, faster, stronger, etc over time because these traits help an individual survive, it doesn't on its own explain certain traits that would not help until they were developed. My knee-jerk response was "a random mutation got the ball rolling" but I was at a loss beyond that to explain why a certain mutation would ever develop if it was of no help before it developed.

As you guessed by my topic, I got skunked by the skunk

The thing with the skunk, it isn't terribly perceptive, fast, camouflaged etc because of its lovely defense, but how did it develop that defense? If some random mutation resulted in a rodent that could squirt some sort of puss or blood or whatever, it would still instinctively try to run if a predator came close and would never have utilized it to help itself survive. Also, since its spray isn't anything to be frightened of until it evolves potency, running would seem to offer a better defense for it until it developed at least some of its current potency.

Anyways, can someone give a "concise, complete dummies guide to the evolution of extraordinary abilities in animals" please? Thanks.

MrDarwin

Well, since the closest relatives of skunks all have musk glands and produce scented secretions of some kind, your friend's position is weakened considerably.

BTW skunks are carnivores, not rodents.

[ June 13, 2002: Message edited by: MrDarwin ]</p>

Yellow3

Argh! 20 minutes worth of reply and the server flipping EATS IT!

. . . anyway, to paraphrase what I was going to say, skunks belong to a family of carnivores that are (among other things) characterized by anal glands capable of producing strong secretions. Hence the name, Mustelidae. The members of at least three separate genii in the family are capable of using these secretions for defense; genus Mephitis (e.g. Striped and spotted skunk), Ictonyx striatus (Zorilla), and Poecilogale libyaca (Libyan striped weasel). All developed the ability to use these glands as chemical weapons. All also share the black-on-white striped patterning. It apparently doesn't take much to turn a mustelid's strong-smelling anal gland secretions, probably originally used to mark territory, into a defensive weapon.

Other amazing animal abilities will frequently become less so when you actually look at them in the context of what they're related to and what the family can do. For example the powerful shock of electric eels, a defensive and hunting weapon, makes more sense when you realize that its relatives are fish that produce a constant electric field about them just so they can "see" their way through murky and tea-like water. So it works with skunks.

Hope this helps,

- Jen

[Edited because, I am entirely too fond of, commas, for my own good.]

[ June 13, 2002: Message edited by: Yellow3 ]</p>

Mageth

Skunks are in the Mustelid (weasel) family, along with weasels, minks, fishers, wolverines, badgers, ermines, ferrets, otters, grisons, martens, polecats, stoats, tayras and zorillas (hey - another animal besides zebras that begins with "z"!)

All have anal scent glands of varying potency. All smell bad.

As far as the "not effective until it developed its potency," bah. Dilute some skunk extract by 50%, or even by 90%, and it'll still knock your socks off. 5% potent skunk scent is more effective and "useful" as defense than no skunk scent. That's all it takes for natural selection to do its work.

It may be that the scent glands originated as a defense mechanism, or perhaps were used to mark territory or for some other purpose. Whichever, the skunk's ancestors may have discharged the (less potent than today's) glands in fear when approached by predators, which may have been enough to frighten off some predators. Individuals who had even slightly more potent scent may have been more successful at frightening off the predators and thus producing offspring. Thus, over time, the natural selection process has produces skunks with the potent scent they have today.

Bible Humper

Thanks for the responses! The thing with these expainations though, is that it doesn't explain how the skunk would go from marking territory to actually squirting it towards predators. Surely, while it was being used to only mark territory, it was neither accurate nor long ranged, correct? Also, how would they start to try this when their instincts would be screaming RUN? One last thing is that they can now perform a cool little balancing act while they aim it at you, but before it was a developed weapon, they would have to rely on "shooting blind" at something behind them.

Thanks for the other info guys, appreciate it.

Mageth

The thing with these expainations though, is that it doesn't explain how the skunk would go from marking territory to actually squirting it towards predators.

You can fill in the gaps, if you think about it. A few examples (admittedly simplifications):

An ambush predator may pounce on the unsuspecting skunk-ancestor Stinky. In fear, Stinky might discharge his scent glands. Getting a good whiff, the predator might run away. If Stinky's sister Smelly didn't squirt, didn't squirt as far, or didn't stink as bad as Stinky, the same predator might munch her down. Stinky survives to produce stinky offspring; smelly doesn't.

Some predators may be too fast to run away from effectively. If Stinky's ancestor Odorous is genetically inclined to squirt Speedy the predator in the face and thus drive him off, but his cousin Doofus is genetically inclined to run and thus gets caught, Odorous survives to produce stand-and-squirt offspring; doofus don't.

Like I said, these are simplifications, and I'm not saying they're exactly correct, but I think you get the idea. The same kinds of selection pressure/survival scenarios may be applied to the handstand posture, the black-and-white markings, etc. If a genetic trait or behaviour provides even a slight survival advantage, it will tend to propagate throughout the population over time.

Note that some characteristics (e.g. stand-and-squirt, handstanding) may be learned behaviors that have been selected for, and are passed down generation to generation, rather than genetically inherited traits (I'm not saying they are; I'm saying such behaviors may be in some species).

butswana

When I drive past a road-kill skunk, I breathe deeply. I like the smell. It reminds me of that dark green sticky reefer shit I used to smoke.
<a href="http://www.skunk-info.org/default.htm" target="_blank">http://www.skunk-info.org/default.htm</a>
I like the blonde ones. They remind me of my favorite animal; the honey badger.

Grumpy

In short, this is the old "what use is half a wing?" conundrum, dressed up with a new (and interesting) example. As always, the simple explanation is that an incipient trait was useful for something else before it was co-opted for its present function.

Mageth

"Co-opted." Thanks, grumpy, I was trying to remember that term.

B_H, if you haven't read it, you might want to read <a href="http://www.amazon.com/exec/obidos/ASIN/068482471X/qid=1024004620/sr=8-1/ref=sr_8_1/002-6385940-6180029" target="_blank">Darwin's Dangerous Idea</a> by Daniel Dennett. If you could get your friend to read it, that would be great.

Duvenoy

Musking is very common defensive behavior and not limited just to mammals. All snakes do it to a greater or lesser extent as well as arthropods such as stench beetles and vinegaroons. Also some turtles musk.

It is not difficult to see how this defense might evolve into actual spraying. Indeed, the cottonmouth (Agkistrodon piscivorus) is capable of blasting out a copious amount of a particulary vile musk. It's not aimed, but there's a lot of it. The bombadier(sp?) beetle has carried this to even greater extremes than a skunk, and is another, futil Creationist argument.

For more on the bombadier, I believe that talk origins has a couple of papers on it.

doov