The Ant and the Blade of Grass

[Lestat]

Daniel C. Dennett likes to tell the story about an ant crawling to the top of a blade of grass. It turn out that the ant's brain can be invaded by a parasitic worm, which need to get into the belly of a cow for survival. Thus (as Dennett puts it), it drives the ant like an all terrain vehicle up the blade of grass so a cow can digest it.

Well, I certainly have a healthy respect for evolution, but just how on earth did this worm evolve to know not only to invade the brain of the ant, but to then have an exact effect on the brain that causes it to climb up the blade of grass? That just seems too big of a stretch for me. Too wide of a gap to be passed on. Btw- I understand the worm doesn't actually "know" anything, but I'm not sure what DOES know. The DNA of the worm?

I have similar questions regarding the behavior of insects... How many times have you seen a spider crawing on the wall and when you went to kill it, it froze. Now I understand that it freezes, because movement makes it more noticable to a predator. Better to freeze. I can somewhat understand a deer or antelope doing this when sensing a lion in it's presence, but only because they have probably seen other deer and antelope (their parents), do it. Even if this was built into their brain through evolution, I could somewhat understand it.

I get how a wing, or spots, or tails evolve (even bi-pedal mammals). It is a gradual yet, beneficial change that gets passed on. But I cannot see how evolution could've hard wired this freezing behavior into an insect's brain. Insects that didn't freeze were eaten. Those that did, survived, but... How did those that survived pass this trait onto their offspring? Maybe I don't understand it, because I'm under estimating an insects intelligence?

[bunny]

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Daniel C. Dennett likes to tell the story about an ant crawling to the top of a blade of grass. It turn out that the ant's brain can be invaded by a parasitic worm, which need to get into the belly of a cow for survival. Thus (as Dennett puts it), it drives the ant like an all terrain vehicle up the blade of grass so a cow can digest it.

Well, I certainly have a healthy respect for evolution, but just how on earth did this worm evolve to know not only to invade the brain of the ant, but to then have an exact effect on the brain that causes it to climb up the blade of grass?

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(Insert usual "I wouldnt really have a clue but..." disclaimer here)

It would seem more plausible to me that it first evolved to live in an ant's brain. An unexpected side effect was that sometimes the ant got driven up the blade of grass, because of where the worm was nestled. Consequently a lot of them got eaten by cows. A few worm larvae or whatever happened to survive. Repeat many times. Gradually, the "living in a cow for a while" bit becomes essential (which would then provide an evolutionary advantage to those ants which happened to live near the "climb a blade of grass" part of the ants' brain)....

[Lestat]

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Daniel C. Dennett likes to tell the story about an ant crawling to the top of a blade of grass. It turn out that the ant's brain can be invaded by a parasitic worm, which need to get into the belly of a cow for survival. Thus (as Dennett puts it), it drives the ant like an all terrain vehicle up the blade of grass so a cow can digest it.

Well, I certainly have a healthy respect for evolution, but just how on earth did this worm evolve to know not only to invade the brain of the ant, but to then have an exact effect on the brain that causes it to climb up the blade of grass?

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(Insert usual "I wouldnt really have a clue but..." disclaimer here)

It would seem more plausible to me that it first evolved to live in an ant's brain. An unexpected side effect was that sometimes the ant got driven up the blade of grass, because of where the worm was nestled. Consequently a lot of them got eaten by cows. A few worm larvae or whatever happened to survive. Repeat many times. Gradually, the "living in a cow for a while" bit becomes essential (which would then provide an evolutionary advantage to those ants which happened to live near the "climb a blade of grass" part of the ants' brain)....

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You are very good at reverse engineering! I didn't think of that. Dennett simply states that the worm "needs" to get into the belly of a cow. So I assumed this preceded all, and that evolution somehow figured out the best way for for the worm to achieve this. But yes, if the cow came afterward, it makes much more sense.

[vhawk01]

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Daniel C. Dennett likes to tell the story about an ant crawling to the top of a blade of grass. It turn out that the ant's brain can be invaded by a parasitic worm, which need to get into the belly of a cow for survival. Thus (as Dennett puts it), it drives the ant like an all terrain vehicle up the blade of grass so a cow can digest it.

Well, I certainly have a healthy respect for evolution, but just how on earth did this worm evolve to know not only to invade the brain of the ant, but to then have an exact effect on the brain that causes it to climb up the blade of grass?

[/ QUOTE ]
(Insert usual "I wouldnt really have a clue but..." disclaimer here)

It would seem more plausible to me that it first evolved to live in an ant's brain. An unexpected side effect was that sometimes the ant got driven up the blade of grass, because of where the worm was nestled. Consequently a lot of them got eaten by cows. A few worm larvae or whatever happened to survive. Repeat many times. Gradually, the "living in a cow for a while" bit becomes essential (which would then provide an evolutionary advantage to those ants which happened to live near the "climb a blade of grass" part of the ants' brain)....

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You are very good at reverse engineering! I didn't think of that. Dennett simply states that the worm "needs" to get into the belly of a cow. So I assumed this preceded all, and that evolution somehow figured out the best way for for the worm to achieve this. But yes, if the cow came afterward, it makes much more sense.

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Its a common problem in discussing topics in evolution, this anthropomorphizing of the process, attributing intent, things like that. The reason is, it makes it easier to describe something by saying stuff like "Ok, so the worm needs to get here, so evolution creates this mechanism." It ends up being misleading and is obviously entirely incorrect, but it makes it more approachable. Dennett is probably the worst culprit of this, although I think Gould does it often and Dawkins also, to a lesser degree. Certainly, it is something that is RAMPANT in science textbooks and popular scientific writing. I always cringe a little bit when I read anyone talking about the goals or tactics or strategies that evolution uses to do things, but I also cringe when I read a general chemistry textbook and they talk about electrons in orbits and such. Its a balance, the writer tries his best, and you must consider the audience. Lestat, by posting here on SMP and reading the evolution debate in a very special context, you have a different perspective than the vast majority of readers. You know enough to cringe when you hear agency bestowed upon mindless processes (mindless added for NRs benefit) but perhaps don't have the experience or the repetition needed to translate those pop-speak phrases into what they really mean.

[vhawk01]

And to answer your OP, I really don't know, but I'd imagine it was very complex and took a long, long time. It has the hallmarks of a scaffolding-type scenario.

[NotReady]

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You know enough to cringe when you hear agency bestowed upon mindless processes (mindless added for NRs benefit)


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I don't cringe when anthropomorphism dominates evolutionist literature. I love it. I especially love the way mindless evolution designs complicated mechanisms when the genius of man can't even understand how. Chance beats purpose every time.

[Phil153]

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You know enough to cringe when you hear agency bestowed upon mindless processes (mindless added for NRs benefit)


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I don't cringe when anthropomorphism dominates evolutionist literature. I love it. I especially love the way mindless evolution designs complicated mechanisms when the genius of man can't even understand how. Chance beats purpose every time.

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If you understood it, you might discover that the world is actually more wondrous, not less, without the petty homosexual slayer and child drowner interpretation that you put on God.

Evolution doesn't design anything. A trillion trillion trillion trials parallel trials performed over billions of years will gradually select for the fittest in ways incomprehensible to the human mind. You really do your God a disservice - his majesty is far greater as a creator and nurturer of a vast cosmic experiment than as homoslayer, the creator of Super Special NotReady on his Super Special Earth. Do you see why?

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As for the OP - I'm not sure why insect freezing is so amazing. They do have brains and nerves centers. The ant story is quite interesting - there are probably simple triggers. It reminds me of toxoplasmosis which causes mice to lose their fear of cats and seek out cat urine, which is advantageous to the parasite breeding cycle. They infect human brains too - a scary read. I guess homoslayer thought that was a good idea?

[TimM]

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Chance beats purpose every time.

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This statement betrays your lack of understanding. It is selection pressure that drives evolution, chance simply provides the variation.

[vhawk01]

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You know enough to cringe when you hear agency bestowed upon mindless processes (mindless added for NRs benefit)


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I don't cringe when anthropomorphism dominates evolutionist literature. I love it. I especially love the way mindless evolution designs complicated mechanisms when the genius of man can't even understand how. Chance beats purpose every time.

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Right, I was talking about Lestat, someone who presumably reads this stuff to learn, honestly, about things he doesn't understand. IOW...not you.

[qwnu]

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Its a common problem in discussing topics in evolution, this anthropomorphizing of the process, attributing intent, things like that. The reason is, it makes it easier to describe something by saying stuff like "Ok, so the worm needs to get here, so evolution creates this mechanism." It ends up being misleading and is obviously entirely incorrect, but it makes it more approachable. Dennett is probably the worst culprit of this, although I think Gould does it often and Dawkins also, to a lesser degree. Certainly, it is something that is RAMPANT in science textbooks and popular scientific writing. I always cringe a little bit when I read anyone talking about the goals or tactics or strategies that evolution uses to do things, but I also cringe when I read a general chemistry textbook and they talk about electrons in orbits and such. Its a balance, the writer tries his best, and you must consider the audience. Lestat, by posting here on SMP and reading the evolution debate in a very special context, you have a different perspective than the vast majority of readers. You know enough to cringe when you hear agency bestowed upon mindless processes (mindless added for NRs benefit) but perhaps don't have the experience or the repetition needed to translate those pop-speak phrases into what they really mean.

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Dawkins wrote the following more than 30 years ago in The Selfish Gene. He was talking about genes, but his comments obviously apply to larger biological units, i.e, organisms:

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Throughout this book, I have emphasized that we must not think of genes as conscious, purposeful agents. Blind natural selection, however, makes them behave rather as if they were purposeful, and it has been convenient, as a shorthand, to refer to genes in the language of purpose...Just as we have found it convenient to think of genes as active agents, working purposefully for their own survival, perhaps it might be convenient to think of memes in the same way. In neither case must we get mystical about it. In both cases the idea of purpose is only a metaphor, but we have already seen what a fruitful metaphor it is in the case of genes. We have even used words like 'selfish' and 'ruthless' of genes, knowing full well it is only a figure of speech.

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So, I think Dawkins has always been pretty careful about this, and, to the extent that he is actually guilty of misleading anthropomorphism, it's not because he doesn't know any better. [img]/images/graemlins/smile.gif[/img]