Did the eyespots of butterflies and moths evolve to deter predators?

_{Denyse O'Leary

July 29, 2008

Intelligent Design}

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For two hundred years, scientists have believed that the eyespots of butterflies and moths evolved to look like large eyes in order to frighten off predators. A bird might think that the bright eyespots are the eyes of a concealed cat, for example.

It sounds logical, but there is a hidden assumption: We are assuming that a predator such as a bird pays attention to the same features that we would.. But does it?

Cambridge behavioral ecologist Martin Stevens and his team decided to test the longstanding assumption:

Go here for the rest.

Comments

Meh, no answers. Can you guys get some response going? ta-ta E.Torvon_{August 17, 2008
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D'oh, can't edit my posting ... I forgot the answer to your question, and would like to add it: Your question: "Did the eyespots of butterflies and moths evolve to deter predators?" The answer is in the abstract of the study you quote: "Recent work has indicated that spots [...] reduce the risk of predation [...]." ta-ta E.Torvon_{August 5, 2008
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Interesting blog, I see some contradictions though. I sincerely hope - since I'm really putting effort into this posting, as I'm not a native speaker - that you will allow criticism here. Browsing over some comments on this webpage, it's basically a "yes all posters have the same opinion" thing, which is not helping much in order to gain knowledge. (1) Let me point out the bigger contradiction first: I've just finished Paley's "Natural Theology" (1803), a very interesting ID manifest. Now, seen from an evolutionary perspective, Paley proves evolution with all his examples. Scientifically proves it. So do around quadrizillions of other books, studies, papers. It is undeniably true that the HI virus evolves and adapts to specific forms of transmission (which is one out of - again quadrizillions - proven facts, we're not talking about theory here). Now, you guys say that this science is wrong. "The actual content [...] has been corrupted". You quote a scientific study in this posting here. So there is all that "bad" and "not true" science, and the facts get denied, but then again you quote "true" and "proper "science"? Forgive me if I got that wrong, please correct me on that matters. Behavioral Ecology is a very well renowned Journal, one I personally like a lot. It's mainstream science. So what makes this article a good article, and the other articles bad articles? (2) The second contradiction is the point you make itself. The study (after careful reading it) doesn't hold one single point against evolution. The marks on the wings of the moths/butterflies developed as adaptation in order to reduce the risk of getting eaten. It doesn't matter at all which forms or shapes the marks are, if they are in the form of an eye, or of en elephant. From an evolutionary perspective, it is an adaptation that serves its purpose. ta-ta E.Torvon_{August 5, 2008
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Perhaps the Martin Stevens et. al. study experimental design was flawed, because it didn't consider that the birds might be able to detect that the "butterflies" were paper with a big metallic nailhead in the center. Then they wouldn't care whether the spots looked like eyes or not - they were objects with food attached. If this is the case the study is really a "no test" rather than evidence against the "just so" story.magnan_{August 1, 2008
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Thanks, Tom. Hope you get on the mend soon. "I also think poison dart frogs are impossibly beautiful." And perhaps that is the real why . . .Eric Anderson_{July 31, 2008
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Apologies for the flippancy, folks. Between this head cold, and the remedies I am taking for it, I'm not quite 100%. Read the third paragraph (above) first. Eric, you raise interesting questions, no doubt the kind that motivate people like Martin Stevens to do what they do. Making up stories can't be nearly as much fun as finding out whether or not they are true. And so off to bed I go. I meant what I said about poison dart frogs, however. Hard to believe something alive could have that much saturated color.Tom MH_{July 31, 2008
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Being conspicuous should be a rather unoccupied environmental niche, and therefore one into which poisonous species could readily expand. Probably not too difficult to exert selective pressure on predators not to eat them, since there shouldn't be many other conspicuous-but-non-toxic critters already in the environment for which the predators have developed a fondness. The few predators that decide to try eating the bright blue thingie are quickly selected out of the population. Being camouflaged, however, is a niche occupied by other critters likewise trying to avoid being eaten; it would be tough for the poisonous prey to exert selective pressure on the predator, since the predator has to eat and other prey are going the camouflage route. Also, camouflage carries with it other costs and constraints (must always crawl slowly on this kind of tree trunk, etc.). I'm making all this up, of course. The local evolutionists can correct my errors, the front-loading proponents may salute my implicit teleology, and the rest of you can feel free to label these "just-so" stories. I'm not a biologist (I think I mentioned that elsewhere) but I do love a good story. I'll let behavioral ecologists like Martin Stevens check if the stories are true or not. I also think poison dart frogs are impossibly beautiful.Tom MH_{July 31, 2008
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Tom MH wrote: "Both individuals are dead in this scenario, but the result would be one less individual in the population of predators willing to eat brigthly-colored prey. Thus there is adaptive presure on the population of predators - the ones that eat more plainly-colored prey have higher marginal survival rates." Your statement seems plausible at first, but isn't the point of the brightly-colored idea that there is some kind of deterrent value, thereby marginally increasing the utility of being brightly-colored? In your example, there is no additional deterrent value, it is just a purely random coincidence. Specifically, if a camouflaged creature is also deadly, then there will be "one less individual in the population of predators willing to eat [camouflaged] prey." And if the prey is neither particularly camouflaged nor brightly-colored, there will be one less predator willing to eat prey of that size, shape, coloration, etc. Thus, there is no marginal utility in having particular markings that "warn" a predator, unless there is actual deterrent value and the predator is still around to be warned. The counter-examples and exceptions to the adaptationist "rule" multiply to the point where the "rule" is of zero utility. One can't help but feel that this is nothing more than another hastily-adopted, critically-unexamined, just-so story. Nothing more than speculation.Eric Anderson_{July 31, 2008
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Don't even get us all started on assumptions. Sheeshreluctantfundie_{July 31, 2008
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If deadly, then it seems the adaptation story would only make sense if a second predator were around at the time, happened to notice what the first one ate, and then after the first one died, made a mental note to self to avoid eating something of the same color.
Not necessarily. Both individuals are dead in this scenario, but the result would be one less individual in the population of predators willing to eat brigthly-colored prey. Thus there is adaptive presure on the population of predators - the ones that eat more plainly-colored prey have higher marginal survival rates.Tom MH_{July 30, 2008
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utidjian, let's see: If a creature is toxic, do we mean toxic as in painful, nauseating, harmful? Or do we mean toxic in the sense of deadly? If deadly, then it seems the adaptation story would only make sense if a second predator were around at the time, happened to notice what the first one ate, and then after the first one died, made a mental note to self to avoid eating something of the same color. If not deadly, then the adaptation story could make some sense, although one would still be forced to assume that a predator would remember a non-camouflaged meal but would not remember a camouflaged meal. After all, camouflage helps avoid initial detection, but once the prey is detected, does the predator's ability to remember what it ate really change? I suppose it's theoretically possible that a predator would remember that it got sick from a non-camouflaged prey better than it would remember that it got sick from a camouflaged prey, but that is just an unproven suspicion at this point. At present, it seems like we have just a bunch of stories about how creature A is camouflaged to avoid predators, and thus ensure survival, while creature B is not camouflaged to warn predators, and thus ensure survival. In either case, these are primarily stories, with so many exceptions on either end and such a tenuous link between the trait and the developmental adaptationist path that it strains credulity.Eric Anderson_{July 30, 2008
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Borne, I think the, "However, paper moths that had lots of spots were attacked 30% less often than others. Also large spots were more effective than small ones." and what you mentioned are valid. (It is in the data after all.) Many if not most poisonous-to-eat critters do not have much camouflage. Many if not most toxic critters are brightly colored. It would be an advantage for the critter to indicate its toxicity to the predator, no? Better than being camouflaged or otherwise drab and be caught out. A test bite could be fatal. It could also be to a critters advantage to mimic this coloration if it prevents it from being eaten... whether it is toxic or not. Whether intelligently designed or not it certainly appears to be an advantage to be camouflaged if non-toxic or conspicuous if toxic.utidjian_{July 30, 2008
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Seems pretty obvious to me that pretending the spots serve to look conspicuous as toxic : "They suggest that the insect might be poisonous" is even worse than supposing it was because they look like eyes. How in the world does a bird brain discern what may be toxic or not? Color alone? Colored patterns? Based on what mechanism?Borne_{July 30, 2008
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^ By focusing on a bird'd brain they are just trying to trivialize the big picture.Frost122585_{July 30, 2008
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"Thus, any loud pattern might work. That considerably reduces the load placed on natural selection."
No it doesn’t. The big picture is not the specs of color on the wings of the butterfly- or the response of the environment to it- the big question is why should it be beneficial at all? What are the odds of the butterfly the environment and the specs all existing they way that they do for the beneficial effects they perpetuate? They aren't very high. The big picture remains the same no matter how near sighted DE tries to be. This is the payoff of NFl and information theory. It takes out alot of the subjectivity and specualtion and replaces them with raw odds.Frost122585_{July 30, 2008
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Interesting thoughts, Frost+. The researchers found that the birds responded to lots of colourful spots of any size or shape and were not "reading" eyes. Thus, any loud pattern might work. That considerably reduces the load placed on natural selection. But it equally suggests that we shouldn't expect as much from natural selection as we do. Earlier researchers were primed by their belief in the immense powers of natural selection to believe that the birds were deterred by spots that looked like cat's eyes. Until someone decided to test it, as Stevens has done. Prediction: Serious testing of this type will deflate many more just-so stories.O'Leary_{July 30, 2008
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This is really one of the most interesting prime examples of why unguided evolution and design are in conflict. If the butterfly's defenses were not evolved to protect it against predators then the evolution of it's eye spots is an "absurd" coincidence. If on the other hand, it's eye spots WERE evolved to protect it against the independent character of its environment, then we are forced to conclude that some form of guided evolution or design was at work. This would open up questions that methodological materialists are not comfortable with- hence they took an obvious truth- that "eyespots did evolve to protect butterflies" (other creatures have similar defenses as well) and they interpreted the evidence against such a design or guided evolutionary explanation. Bravo once again to the manifest denial exuberated by the chance worshipers. Some people choose to see the world as it is; others try to “reduce” it to something seemingly more manageable.Frost122585_{July 30, 2008
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So what?... Please keep comments substantial & constructive or don't expect them to appear in the future. -UD admin IrrDan_{July 30, 2008
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I do not know whether the hawk moth caterpillar scares its predators by its snakey markings. But in conscience I had to record that Prof. Stevens offered that pinch of incense to the Darwingod. For the record, I believe it perfectly reasonable that natural selection preserves patterns that assist a life form's survival. The scrutiny has - for a long time - focused on whether it can create complex patterns. That seems increasingly unlikely.O'Leary_{July 29, 2008
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"The researchers concluded that the theory that eyespots evolved to look like eyes has no experimental support." Thanks, Dave. Yet another clear example (albeit a rather minor one, as examples go) of how the Darwinian adaptive traits assumption has led science astray. The idea that adaptation-selection drives the unfolding of life is a corrosive philosophy that has failed true science on so many occasions. Unfortunately, the authors couldn't help but offer another just-so story in its place. But, hey, when adaptation-drives-biology is your game, you've got to keep offering those fun stories . . .Eric Anderson_{July 29, 2008
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