Evolution, function and meaning

This piece arises from some discussion on the last post about the mathematical predictability (lack of) in evolution.

Question: Is this the image of an insect, or not?

GoniurelliawingIt depends what you mean. It’s actually an image of part of an insect that’s caused a minor news stir this week:

GontridensBut as for the “image” on the wing, what does that word actually mean? Can “image” be separated from the teleological concept of “intent”? The news story in question  takes a straight adaptationist line. The images on the wings evolved by mutation and natural selection as obvious defensive mimicry. We know it works because there are plenty of Goniurellia tridens out there in the UAE.

That raises all kinds of questions about the astonishing artistic abilities of good old ND mechanisms. It’s easy to see the “insect”, and why it should have survival value. But even if it didn’t look like an insect, it must have survival value, because there it is – does its remarkable appearance explain its arrival?

If we found an insect with the Lord’s prayer in gothic script on its wings, on the adapationist model it must have survival value because it survived, and it must be possible by random mutation because it was there. Nothing specific is thereby explained, and the biologist has no warrant to do anything but shrug and say, “Nothing to see here except what evolution predicts.” How could it be otherwise? But as  defence mechanism it’s hard to imagine that anything less than a pretty good image would have any survival value at all – and if it did, why refining it to the nth degree would provide much extra benefit.

But is there anything to explain anyway? An entomologist has written a considered response in which he argues that the whole thing is “faces in the clouds”. Other Goniurella species have slightly less insect-like patterns:

Goniurellia-wings-Freidberg-1980

And closely related species have obviously similar patterns that don’t resemble anything much at all, unless predators like Rorsach tests.

trupanea-actinobolaOne of  the commenters on that article suggests that the pattern is likely to be non-insect-like in the UV region used by potential predators. So maybe it’s not defensive – maybe it’s mimicry for sexual selection, since the flies use their wings in elaborate mating displays. Or maybe it’s just a random pattern variation, and only humans see an insect on the wings.

Any adaptive story, if one thinks about it, is considerably weakened by those comparisons with similar species. If mimicry is that good either sexually or defensively, the poor mimics ought to have been replaced entirely by Goniurella or its like. As it is, it’s equally incumbent on us to explain the success of all the other interesting but non-pictorial wing patterns, since each, on the adaptive model, has a selective advantage.

In fact, given the survival of all these variants, both adaptive and nonadaptive explanations leave us with a problem of meaning: we are convinced (or most of us) that Goniurella has ants on its wings. But that is a purely human assessment, whether at the instinctive level, or whether we have some metric of the graphic information that corresponds closely enough to an ant to cross some scientific threshold for similarity.

All we know apart from that is that insects with those patterns do OK. It’s pretty hard to research relative predation (witness the long controversy over peppered moths), but virtually impossible to be sure if the completely-fortuitous-pattern-we-see-as-an-insect makes a difference, and if it does whether the predators are actually taken in by mimicry – maybe G. tridens just smells better than G. omissa.

But, in an ateleological system, Goniurella doesn’t think its wings are ants. The genes didn’t evolve to imitate an ant. And if predators or mates act as if the wings are ants, even if we could be sure of that, we could also be sure that they happen to react to a fortuitous pattern, and not to an image. Stuff just happens.

Mimicry, then, like any function, is a teleogical human theory grafted on to the data to no real explanatory purpose, as far as efficient causation goes.

They still look damned like insects, though.

One might ask whether directed theistic evolution provides any better explanation. The thing is, I’m not sure such explanation is strictly necessary, though of course theistic science is about trying to think God’s thoughts after him where possible. Materialist science must explain everything in the Universe by cause and effect, because that’s all there is. In theism there are other levels of causation not amenable to scientific investigation. If we believe it’s an adaption for mimicry, though, some teleological component certainly seems more plausible, to me, than random variation alone, whether that be internal or external.

But theistic evolution no more has to be adaptive than neutral theory. God might do variation for its own sake, and might well be thought more likely to indulge in aesthetics, knowing the outcome will not be disadvantageous, than blind evolution, which one might expect to cling on to what actually works. For God, the occasional insect portrait (or Lord’s prayer on a fly’s wing, for that matter) might even be a nod to us and our penchant for image-making.

Jon Garvey

About Jon Garvey

Training in medicine (which was my career), social psychology and theology. Interests in most things, but especially the science-faith interface. The rest of my time, though, is spent writing, playing and recording music.
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18 Responses to Evolution, function and meaning

  1. pngarrison says:

    As it happens, this turned up on my Facebook feed a few days ago.

    http://www.mymodernmet.com/profiles/blogs/kjell-bloch-sandved-butterfly-alphabet

    Of course they had to crop the photos closely to isolated the “letters” from the rest of the pattern.

    • Jon Garvey Jon Garvey says:

      pngarrison

      I love it! A bit of careful genetic egineering and we’ve got our Paternoster! Or we could commercialise it and release a million “Drink Coca-Cola” butterflies. I remember visiting New England and seeing a question mark butterfly, noting its similarity to the British comma – looks like the lepidoptera are working hard on the punctuation issue, too.

  2. Sy Garte Sy Garte says:

    I remember a nature show or perhaps one of those nature films, where it turned out that some fish living in extremely deep water, where there is no light, have amazing colors. All kinds of colors, spread in a patch work. And of course, there is not purpose to these colors, because most animals in that environment are blind and there is no light. So why the colors?

    The answer is not that difficult. Mutations causing changes in surface coloration, whether the whole skin or in patches are simply not selected against, so they accumulate. The colors do no good and no harm. In fact they don’t really exist as colors (being invisible in the absence of light) until the unnatural act of being caught by a human and brought up to the light.

    I cant help thinking there is a profound philosophical and theological meaning here, just our of reach of my poor tired brain

    • Jon Garvey Jon Garvey says:

      Sy

      Not so much a meaning – more an observation. In non-providential science, the cause-effect mechanism you describe means there is no reason for the pigmentation apart from randomness. Maybe that’s the legitimate last conclusion if science is the study of efficient causes.

      In providential thought, God does it for a purpose, which may be quite opaque to us, but (unlike the other model) even includes what is seen when a human brings it to the surface. That may not add to the science, but it precludes the human conclusion that efficient causation is all there is.

      • Sy Garte Sy Garte says:

        Jon

        That is sort of what I think I might have been getting at. Here we have these fish with truly breathtaking vivid colors on them, never seen by any creatures. Clearly there can be no purpose to such a thing, from any scientific perspective. And yet, along comes man, with his technical innovations, goes to the deep sea, catches some of these fish, and films them in the light. And I, watching all of this on my TV, get a sense of pleasure at the beauty of nature, even when it is hidden for millions of years. So there was a purpose. And only God, the creator of man, could have conceived of that.

        • Jon Garvey Jon Garvey says:

          Sy

          You’re maybe familiar with my mantra (filched from N T Wright) that part – a big part – of man’s image is to express the Creation’s worship to God on its behalf.

          A tree, or a cow, or a deep-sea creature, worships simply by being. But if a rational creature gives thanks and praise for it, God is glorified more.

          That, of course, is also the answer to those who say billions of years of life, death and evolution is “pointless”: reconstruct a Triceratops or a Devonian ecosystem and you’ve revealed some more of God’s living handiwork for which to glorify him than would fit into the world now.

      • Lou Jost says:

        That is an extraordinarily odd way of thinking. Can there be no accidents in your world?

        • Jon Garvey Jon Garvey says:

          Accidents from whose point of view?

          • Lou Jost says:

            Do you guys think all events have a purpose?

            • Jon Garvey Jon Garvey says:

              Lou, think in terms of two opposing worldviews.

              The atheist believes that existence, and all that arises from it, are brute facts without intrinsic purpose. Everything then is ultimately an accident, including deliberate planned human acts. How could it be otherwise?

              An “accident” in evolution is an oxymoron, for evolution is an accident, albeit a productive and directional one. What is more non-accidental, in the end, about elegant insect mimicry than the random drift of unseen submarine pigments?

              The Christian tradition is that, au contraire, material existence itself, and all that arises from it, comes finally from the rational will of the infinite and eternal God.

              Everything, then, is ultimately part of that purpose, including those accidents that happen to us. How could it be otherwise?

              If God is the source of everything and plans, creates, sustains and governs what he has made, where is a “lack of purpose” or an “accident” going to come from? From the omniscient Planner’s lack of foresight? From something outside the One who is all in all?

              • Lou Jost says:

                OK, agreed: in that sense, from my point of view, there are no higher purposes, and from your point of view, there are no accidents.

  3. Lou Jost says:

    “But even if it didn’t look like an insect, it must have survival value, because there it is.” “As it is, it’s equally incumbent on us to explain the success of all the other interesting but non-pictorial wing patterns, since each, on the adaptive model, has a selective advantage.” No, some characters are due to genetic drift and are selectively neutral or even slightly harmful. Population genetic theory shows exactly how much selective advantage is needed to remove harmful variants, for a given population size (it is harder to get rid of harmful variants when populations are small).

    That mistake is made by many evolution denialists, and is understandable if you forgot or never studied population genetics. But the rest of the post is not even attempting to be faithful to the science. Mimicry has obvious fitness value, and this can be (and often has been) proven with artificial models and real organisms. Your rhetorical questions about how mimicry could arise had been answered more than a hundred years ago. And asking why the bad mimics haven’t evolved to be like the good mimics is just a version of the creationists’ silly retort “If humans evolved from monkeys, how come there are still monkeys?”

    Adaptive explanations are testable. It would be easy to see if the ant- or spider-like markings of this fly are important to courtship, or whether they scare predators, or both, or neither. Phylogenetic studies could suggest what their ancestors looked like. Etc.

    • Jon Garvey Jon Garvey says:

      Lou

      The neutral theory explanation was in the next paragraph – did you miss the linked article?

      • Jon Garvey Jon Garvey says:

        Regarding the man/monkeys remark, I suggest there is a significant difference in the cases.

        Genus Goniurella appears to have 9 known species, with very variable images on the same general pattern and overall morphological near-identity – the plate in my article shows the most similar and insect-like wings (though some are much less pictorial). Others, like G. eberjeri whose picture I also managed to find, are scarcely insect-like at all.

        Yet 7 of those 11 overlap the distribution of G tridens in the middle east: ebergeri, for example, being found in Oman.

        Near-identical species in the same range, differing morphologically only in that some show “obvious mimicry”, and some don’t, cries out for an explanation of why there is not species-selection pressure in favour of the mimics. Men and old-world monkeys occupying different niches clearly are a completely different case.

        For that reason, I warm towards Morgan Jackson’s neutral explanation, in efficient causation terms, in which case the “obvious mimicry” would be “obviously mistaken”. Yet they still look damned like insects, etc.

        • Lou Jost says:

          By the criterion you use for the flies (geographic overlap), men and some Old World monkeys also overlap. Because you are human and know a bit about the habits of men and monkeys, you can see that they have different ecological niches. The same can be true of flies. They can prefer different types of vegetation, different strata, or different food sources, each with different predators. Some may do their courtship out in the sun, others in the shade. Etc. Generally evolution does drive closely-related species into different niches.

        • Lou Jost says:

          The neutral theory might be right. But it is a testable hypothesis. You say “mimicry, then, like any function, is a teleogical human theory grafted on to the data to no real explanatory purpose, as far as efficient causation goes.” I don’t see that. Once some random pattern in the wings begins to be interpreted by some predators as potential threats, flies carrying random variations of this pattern which fool predators will produce more offspring than flies with variations that do not fool predators. Over time, this pattern will become better at fooling predators. This is a complete, causal explanation for the existence of mimetic patterns, and it is testable. It might be false in this case; since humans are not the fly’s predator, our reaction to the wing pattern is not very important. But the selective advantage of mimicry is known to be large for many mimics.

        • Jon Garvey Jon Garvey says:

          Re “obvious mimicry” see this – courtesy of my brother.

          • Lou Jost says:

            Cute. I am sure you realize that was made via photoshop, not evolution.

            I’m surprised at how you have misrepresented evolutionary theory throughout this post. For example:
            “Any adaptive story, if one thinks about it, is considerably weakened by those comparisons with similar species. If mimicry is that good either sexually or defensively, the poor mimics ought to have been replaced entirely by Goniurella or its like.” The strength and direction of natural selection will be different in different niches, and caan start at different times. If evolution is real we should expect to see “work in progress” as well as good examples of mimicry, and that is what we see.

            “Mimicry, then, like any function, is a teleogical human theory grafted on to the data to no real explanatory purpose, as far as efficient causation goes.” It does have explanatory power, as I mentioned in an earlier comment. Things that happen to be better at fooling predators will leave more offspring, on the average, than things which happen to be worse at fooling those predators. This will move the whole population to better and better levels of mimicry. We can test the mimicry by experiment, and we can in principle quantify the fitness advantages, and we have a solid mathematical theory that tells us how fast the population will change given those fitnesses.

            And if you have ever spent much time watching insectivorous monkeys or birds combing the forest for food, you’d realize that the selective pressures are huge.

            Your preferences, teleological explanations or divine amusement, suffer greatly by comparison with real science.

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