There’s a reason why all vertebrate wings are modified legs of their terrestrial ancestors

But don’t ask the IDists to explain it.  They can’t, and as usual, they avoid addressing anything (other than to complain that “it’s too complex too evolve”) that shows up their claims, which is just about every complex biological organ or system.

I am posting about vertebrate wings and how they are all as divergent from each other–and dependent upon unlikely “design” choices–as evolution predicts, in order to drive home the point of yesterday’s post, as well as many of the earlier posts.  The strangeness of the “designs” claimed by IDists are too often let go by without much argumentation, yet it is truly odd from a design standpoint that the two adaptive immune systems share none of the same parts except the genes inherited from the vertebrate ancestors from which the two lines diverged, and that evidence of “similar authorship” of subsequent change is completely absent (as predicted by evolution).  Vertebrate wings are just another example of the fulfillment of this evolutionary prediction, only the “physical precursors” (DBB, 45) are patently unpromising from a design standpoint–and clearly some vertebrate wings are rather better than are others.

Pterosaur, bird, and bat wings are all homologous, of course, but only through their shared ancestry of reptilian forelimbs and feet. Here is a source showing the morphologies of pterosaur, bird, and bat wings.  All vertebrate wings are analogous as well, but all had to evolve from legs, and not from the wings of unrelated animals.  Pterosaur wings evolved from archosaur legs, and bird wings did as well.  Only, by the time birds evolved, the archosaurs had evolved into dinosaurs (and other organisms), so that bird wings evolved from dinosaur forelimbs.  Bat wings evolved from mammal forelimbs.

And how does this compare with design?  Well, however strange it may seem to IDists, the Wright brothers studied bird wings, not mammal or reptile forelimbs, to assist their own attempts at achieving flight.  They also used “first principles” and empirical studies, so that their airplane’s wings were hardly mere modifications of bird wings.

Yet we are to believe that a “designer” capable of creating extremely complex systems–of the kind that humans cannot presently create–went back again and again to legs in order to design vertebrate wings.  Which is just as evolution predicts, in the tetrapod context.  Would anybody ever expect that of an alien?  Really, no, because it does not fit with our conception of rationality and intelligence.  Legs (forelimbs, anyhow) only have some of the musculature and skeletal strength needed for wings, they have none of the shape or detailed structural components needed for wings.

To be sure, birds were fortunate to evolve their own wings, rather than to copy the previously-existing pterosaur wings.  The latter were not at all bad structures, but they were unlikely to do well with a tear.  Even more importantly, presumably, the evolution of feathers provided birds the chance to evolve truly superb airfoils.  Birds have come near to optimizing aerodynamics, thanks to the fact that they inherited from dinosaurs the ability to grow feathers at varying lengths and in different morphologies.

Ah, well, maybe the designer was learning, after all.  However bizarre such an “argument” may be, IDists will try anything out to save their beliefs, so we’ll go through this “hypothetical” as well.  Pterosaurs came first, then birds, and last of all, bats.  The designer could have tried out pterosaurs, then bettered itself by inventing birds.

As anyone reading this must have anticipated, that is hardly the way to save “design” of bird wings, even if we neglect the unlikely starting points, namely, the unpromising terrestrial forelimbs.  Because, clearly, the bat wing is not an improvement on bird wings, in fact it is step back from the wonderful aerodynamics of birds with their feathers.  Bats fly well enough, but one reason they hang upside-down to sleep is because they do not have the flying power to simply take off from a perch, as a bird does (yes, birds also “jump” into the air, yet that is nothing mammals could not evolve to do as well).  Bats are not the fliers that equivalently sized birds are, not only because evolution deprived them of feathers, also because they do not have the efficient breathing apparatus that birds evolved from dinosaurs. 

At least bat wings are less likely to suffer badly from tears than pterosaur wings were, which hardly makes them equal to bird wings in flight ability.  Modifying legs into wings is as unpromising a “design strategy” as any unprejudiced person would assume at first, but it was the only route open to the evolution of vertebrate wings (unless we count “flying fishes,” but their “wings” are modified pectoral fins, from which tetrapod forelimbs evolved, so nothing substantively changes by imagining their evolution of true flight (surely it could happen)).

I have asked several IDists, including Paul Nelson, to explain this extremely odd “design strategy,” and of course I was met with absolutely no answers to the “riddle,” although I was often “treated to” irrelevant and repetitive ID claims.

I think that this particular focus puts the evolution of adaptive immunity into perspective.  At this point we really cannot point to either agnathan (hagfish and lampreys) or to gnathostome (jawed vertebrates) and say that one of them has the “best” adaptive immune system.  In fact, at the present time they appear to be fairly comparable, at least in numbers of recombinations possible to “adapt” to the threatening pathogen.  Vertebrate wings, however, are fairly easily compared, and the comparison produces a true winner in bird wings.  Furthermore, we know how designers have gone about making wings by looking at organisms, and they neither stuck anywhere nearly as rigidly to their organic “prototype” as IDists claim that their god did, nor did they look to legs as promising wing material.

This, then is the primary lesson of adaptive immunity.  The point is less what system is “better than the other,” but is more that organisms fit the only causes available to unguided evolution in every respect.  To put it in “authorship” terms, no designer could be convicted in a court of law for copying the design of one vertebrate wing to another vertebrate wing, or of one adaptive immune system to another one, for no similarities (other than limitations of inheritance and of physics–homology and convergence, that is) exist between them.  Adaptive immune systems and vertebrate wings share homologies, due to common ancestry, but no similar thoughts from the same mind is responsible for the modifications of their respective common inherited genes, in either vertebrate wings, or in the two adaptive immune systems.

If one were really interested in predicting that organisms were designed, one would insist that a common intelligence behind various designs would leave its mark upon organisms.  And it is because evolution passes all realistic tests of its predictions, including the lack of “common authorship” of the modifications occurring in divergent organisms, that Behe demands virtually supernatural knowledge of the specifics of evolutionary developments that took place so long ago, and for which so much of the evidence has been lost.  Behe’s problem with evolution is avoiding the fulfilled predictions of unguided evolution, along with avoiding any realistic predictions of design.

This is part of a series of posts that I am combining into one long post, which may be found at Darwin’s Black Box.

Explore posts in the same categories: Darwin's Black Box

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5 Comments on “There’s a reason why all vertebrate wings are modified legs of their terrestrial ancestors”

  1. […]  In this linked post I made the point that pterosaur and bat wings are “poorly designed”… Again, though, that is only the minor issue pointing to the greater issue, which is that, for example, bat wings are simply the way that they are because of the constraints imposed by (unguided) evolution upon the modification of mammal forelimbs into wings.  The problem that IDists need to explain is why “design” follows constraints of evolution, not the constraints of any known intelligence, when it produces bat wings.  Any number of factors might cause a designer to produce a less than stellar design, of course, so the important question is why the only identifiable factors behind “poor design” in organisms are the constraints of unintelligent evolution. […]

  2. Paper Hand Says:

    Don’t bat wings have certain advantages over bird wings, though? As I understand it, bats are far more maneuverable in flight than birds, which is bats dominate the aerial insectivorous niche (their sonar certainly helps there, too, of course)

  3. glen1davidson Says:

    That’s a good point, Paper Hand. Bat wings are much more articulated than are bird wings, so more flexible, which presumably is valuable for insectivory.

    On the other hand, bird wings have become reduced in articulation and flexibity since the time of Archaeopteryx, although I believe that feathers allow for more maneuverability than the bones themselves would suggest. And the maneuvers of a swallow are actually quite remarkable, and a hummingbird’s even more so (the hummingbird benefits by being smaller, though). Flexibility has its value, however birds have evolved for less skeletal flexibility.

    There are some sources which claim that bats are more efficient fliers than birds (but they seem to be comparing very small birds and bats–neither of which would seem to be likely to evolve to be highly efficient distance fliers), in fact. My sense of the sources, however, suggests otherwise, and below is a quote that I think summarizes the relative merits and demerits of bird vs. bat flight:

    “In contrast to birds, some of which hover easily or travel huge distances, bats—the other group of flying vertebrates—seem to be rather second-rate flyers. There are a few ‘flower bats’ that are able to hover, but only close to sea level. “Although bats can hover transiently, perhaps up to a minute, they cannot hover for as long as hummingbirds or insects,” said Douglas Altshuler, Assistant Professor of Biology and an animal flight specialist at the University of California (Riverside, CA, USA). Furthermore, although bats travel significant distances in search of food, their range tends to be around 800 km at most, while birds migrating between the Arctic and Antarctic cover more than 15,000 km. Avian adaptations have allowed birds to conquer almost the whole world, both in terms of latitude and altitude, and also to perfect hovering to an extent that bats have never achieved.

    “But it would be a mistake to consider bats inferior to birds. They have fundamentally different wings and, although birds win in terms of efficiency and stamina, bats have the edge in aerobatic ability. Bat wings are extensions of mammalian arms and are formed by membranes with double layers of skin that join the bones of the fingers. The membrane contains a combination of muscle and elastic fibres to keep it stiff but enable it to fold. Bats can use their ‘fingers’ to adapt the shape of the wing to perform the highly precise acrobatic movements needed to catch insects in the air.”

    So yes, bats seem to have the type of flight that is useful for insectivory, while birds (especially larger birds) appear to have more efficient flight overall. Which presumably is not surprising, considering why most bats fly. On the other hand, it is not at all obvious that fructivorous bats have a particularly good means of flight for their needs, although it is certainly adequate to get to the fruit.

    Indeed, bats also do not have the visual capabilities of birds, which presumably is why they are night fliers, with only a few birds like the owls also flying at night. Each has its advantages, which gives them their particular niches.

  4. Paper Hand Says:

    Thanks for the response. And that’s certainly a good point about fructivorous bats.

    I find it interesting how all four examples of powered flight use different wing-designs, with the insects’ being especially different from the vertebrates. I sometimes wonder what other possible wing designs there could be if other groups of vertebrates were to evolve flight, perhaps in the course of future evolution, or in a sort of parallel universe where evolution took different courses.

  5. […] Behe’s “arguments,” such as the fact that Behe manages to explain nothing about the lack of “common authorship,” after lines have diverged, of the various vertebrate wi…  But the poor analogy of life’s machinery with designed machinery is certainly not a […]

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