Monday, 23 April 2012

Seeing Eye To Eye With A Butterfly

Peacock Butterfly
Eyes to die for!

Well, eyes to live for actually.

So, what on Earth is an insect doing with such obviously mammalian 'eyes' on it wings, albeit eyes that can't see? You would think a tasty morsel like that would want to keep hidden and not have bright colours advertising it, wouldn't you? They surely can't be there for us to admire, can they?

But of course, it has nothing to do with us. It has to do with birds!

You see, to find a mate, the butterfly needs to advertise itself, and reproducing is what it is for. But it needs to avoid getting eaten too, so we have a classic tension leading to an equilibrium where finding a mate needs to be balanced against the need to avoid being eaten - at least until after it's found a mate and produced eggs for the next generation.

Enter our predatory bird.

This bird needs to find food for itself and it's chicks and it also needs to avoid being eaten. So again we have another equilibrium resulting from the tension between finding food and being exposed to predators.

Let's see things from a bird's eye view.

An upside down butterfly.

But cover the fore wings and what do you see?

Fox
Or maybe:

Stoat

You see, the birds who survived were those who didn't stop to think, "Oh! What lovely eyes!", because those would be eyes to die for, but those who were up and away before they even knew what their wings were doing. Those who did it best left more descendants, so a rapid flight response to a mammalian eye evolved in the presence of mammalian predators.

Now what has this got to do with the Peacock Butterfly? We'll, birds with these super-fast reflexes were in their environment and were trying to eat them, so, whilst the butterfly was needing to evolve ways of attracting a mate without being eaten, it happened upon a pattern which looked a bit like the eyes of a fox or a stoat, or some other predatory mammal, which is what the bird's genes needed not to be eaten by.

To begin with, the marks might not have looked very much like mammal eyes just so long as in poor lighting or for birds with poor eyesight, they triggered the flight reflex. As the survivors with these slightly eye-like markings became more numerous it was those on whom natural selection worked, so the eye marks became more eye-like and better at attracting butterfly mates.

Also, the butterflies who carried genes which meant they found the eye-like markings attractive would have left more descendants because those genes would have benefited from the presence of genes for making the eye-like markings, so sex-selection would have reinforced this evolutionary process.

From the bird's genes point of view, it was a better trade off to miss a snack than to be eaten. From the butterfly's genes 'point of view' (it's a metaphor, don't get over-excited) it was better to avoid being eaten and to find a mate. Win:win for the butterfly genes and a powerful driver in favour of greater and greater perfection. But perfection not in looking exactly like mammalian eyes but in triggering the flight reflex in the bird. So, maybe two sets of eyes worked better than one, and additional marks which make it look like the eyes are coming closer were even better.

All it has to do is open it's wings and flash those eyes, and the same mechanism works with a prospective mate too!

So, we have insects with mammalian eye-markings because their predators were preyed on by mammals.

And all the butterfly was trying to do was find a mate and avoid getting eaten. Now, what intelligent designer would have have designed that, unless it was one who loved watching birds get the surprise of their lives and denied a meal with a trick?

Snake
Atlas moth

Atlas moth and 'snake'. Not too hard to work out what eats the atlas moth's predators. Go on! You know you can.




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9 comments :

  1. Woyundao.

    Please do not spam this blog with advertising.

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  2. Chanpart

    Please do not spam this blog with advertising.

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  3. As you know, loving your work - however...
    "so, whilst the butterfly was trying to evolve ways of attracting a mate without being eaten, it happened upon a pattern which looked a bit like the eyes of a fox or a stoat"
    As the post states, those butterflies' wings sprang from a random mutation which looked a bit like eyes, they didn't get eaten, their
    offspring survived and so the mutation flourished. However, they didn't 'happen upon' the mutation, the predators instinct formed the
    evolutionary path of the original random mutation, the butterfly wasn't 'trying' to achieve anything.
    Whilst overall the post and the information it imparts is correct, the choice of words above, as with many eminent scientists and TV presenters, have involuntarily imbued the animals with a knowledge of outcome, or purpose, that is absent from the evolutionary process.
    The butterfly doesn't know the birds don't eat it, let alone that they don't eat it because of the camouflage. They don't even know it's camouflage, it might not even know there are birds, to the same degree of ignorance as the bird, which doesn't know that the fox it just avoided wasn't a fox.
    As I said it's common and I think mostly, as is the case here, there's nothing devious in it; I'm pretty sure it's just down to brevity. Stephen Fry is even guilty of it. On a program he was presenting about some animal or other, he once said "...and it stores it in special glands in it's neck" whereas if he were to say "and specialised glands have evolved in its neck to store it" the meaning would have been retained without the accidental transmission to the listener of any implication that the animal had a desire for or chose the ability, body part or trait.

    As your and my goal seems the same, the eradication of misinformation, I hope you hear this in the spirit it's intended.

    ReplyDelete
    Replies
    1. You are quite right of course. There is no determination or plan in evolution. I was using a rather lazy metaphor (a short-hand maybe) for the superficial appearance of determinism. Because the outcome is often so similar to what we would expect of an intentional process, looked at with the hindsight of knowing the outcome - in this case a wing-pattern which both attracts a mate and deters predators - it is often easier to express it in those terms.

      I don't suggest a butterfly has a conscious thought process like us but I think it's fair enough to talk about trying to find a mate or trying to avoid being eaten but certainly not in terms of trying to evolve a specific solution. Evolution of course is a change in allele frequency and takes place at the gene-pool level and not in individuals so there is no way an individual could influence that even with a desire to.

      Thanks for pointing that out and giving me the chance to clarify it.

      Delete
    2. Thanks for the clarification, I thought as much.
      I wasn't attempting to imply you, or the post were, or are, suggesting 'cognitive choice' but I find I must press the point about 'trying'. I feel 'trying', specifically in a description of any aspect the evolutionary process, implies 'cognitive decision' or at the very least 'conscious will', as an intrinsic property of the word. I do understand what you mean by "it's fair to say 'trying'" but others may not and, in the current climate were it seems so few have a real grasp of the natural selection process, even the smallest, unintentional misdirection, can confuse a novice. I just have a hunch that in world were the majority seem to think their 'Casper' 'drives' their body around, it's all to easy for those new to evolution to misapply 'spirit driver' to the 'conscious will' undertone of 'trying'.
      I realise it seems a bit pedantic but I do think it's important.

      Delete
    3. You're right again of course. It IS important.

      Delete
  4. "The butterfly doesn't know the birds don't eat it, let alone that they don't eat it because of the camouflage. They don't even know it's camouflage, it might not even know there are birds, to the same degree of ignorance as the bird, which doesn't know that the fox it just avoided wasn't a fox."
    So its possible that the human species are camouflaged and unaware of it. It is possible there are human predators out there that we are completely unaware of. Perhaps we are not the top of the food chain? Just remember how sure we used to be that the sun revolved around the earth and how sure we were that we were the center of the universe. Just an interesting thought to entertain...........

    ReplyDelete
    Replies
    1. An interesting premise for a short story muse but I think it would have to be set in a parallel dimension, the knower's of sciences would be poo poo it like a swarm if it were set in our universe with statements like, the bigger the brain the greater the awareness of environment.
      Scary thought though that there may be some alien/species that is more capable than humans. Hope the camouflage holds. :)

      Delete
    2. Is there any evidence for these 'human predators', by which I assume you meant predators on humans, other than imaginary?

      Delete

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