The Case for a Creator: The More Things Change

The Case for a Creator, Chapter 3

Strobel’s discussion of embryonic similarities with Jonathan Wells leads into a broader discussion of homology, which deserves its own post.

I’ve been harder on Wells than I otherwise would because he, unlike the vast majority of creationists, has a legitimate degree in biology. It’s impossible that he doesn’t understand some of the things he claims not to understand, or that he doesn’t know the actual scientific explanations for the questions he poses. That being the case, there’s no explanation for many of the confusions or patently false claims he makes, other than that he’s deliberately attempting to deceive lay readers. This post will point out some examples of that.

To get our definitions straight, homology is a detailed similarity of organization that is functionally unnecessary. The streamlined shapes of fish and dolphins are not homologous, because they can be explained by similar adaptive pressures acting on both species to increase their swimming speed. But the fact that both humans and dolphins have five finger bones (in dolphins, buried in their fins) is an example of homology, because no adaptive necessity that we know of would compel such a similarity of structure. In fact, nearly all mammals show this striking pattern, even though their limbs have been radically modified to serve purposes as different as swimming, burrowing and flying:

Below: Examples of homology in vertebrate limbs: Bats, moles, and dugongs all have five fingers. From Carl Zimmer, At the Water’s Edge, p.58.

Vertebrate Homology

“Actually, these homologies were described and named by Darwin’s predecessors – and they were not evolutionists.” [p.52]

From the emphasis Wells puts on this statement, it seems we’re meant to find it shocking. I don’t know why he thinks we should be surprised that scientists who predated Darwin were not evolutionists. Is the argument here that if something was first noticed by non-evolutionists, it can’t be used to support evolution? That would be a ridiculous distortion of how science works.

As with the similarities in vertebrate embryos, the homology among living creatures is an observation. Evolution is an explanation for that observation, and many others as well, which shows how a wide variety of observed facts can spring from the root of a single unifying principle. That’s how science is meant to work. No one scientist “owns” an observation, nor are they the final judge of what theories it can be used to support, even if they’re the one that discovered it.

Wells goes on to claim that homology can’t be used as evidence for evolution unless we understand how it arises. This is a fair point, but the explanation is obvious, though he tries very hard to make it seem incomprehensible:

“A more common explanation nowadays is that the homologies come from similar genes. In other words, the reason two features are homologous in two different animals would be that they’re programmed by similar genes in the embryo. But it turns out this doesn’t work very well…
    There’s a gene that’s similar in mice, octopuses, and fruit flies. If you look at a mouse eye and an octopus eye, there’s a superficial similarity, which is odd because nobody thinks their common ancestor had an eye like that. What’s more striking is if you look at a fruit fly’s eye – a compound eye with multiple facets – it’s totally different. Yet all three of these eyes depend on the same or very similar gene.
    In fact, it’s so similar that you can put the mouse gene into a fruit fly that’s missing that gene and you can get the fruit fly to develop its eyes as it normally would.” [p.53]

Wells claims that this is a deep mystery and an insurmountable difficulty for explaining homology, but it’s neither.

In addition to creating proteins which do the hard work of building body parts, genes can also turn other genes on or off. Genes like the one Wells mentioned (its actual name is eyeless, because of the effect on development when it’s knocked out) are master control switches. When activated, they set in motion an entire cascade of other genes. It’s differences in those downstream genes that create the differences between mouse, octopus, and fly eyes, but the initial genetic switch that kicks off this program is very similar across species – so similar that, as Wells notes, the mouse eyeless gene can trigger the development of eyes in fruit flies.

This is the explanation for homology that Wells claims not to understand. When we see these homologies, what we’re seeing is alterations of a developmental program. All mammals have inherited a toolbox of genes from their common ancestor which they use to do things common to all mammals, such as building limbs. In every mammal species, the same master control switches are there; the same genes building the same body parts are there. But the program has been altered by selective pressure – turning some genes on for longer, or suppressing others sooner – to change the limbs in ways that are adaptive for various different niches.

This leads into Wells’ next distortion, about the genetic similarities between humans and apes:

“If you assume, as neo-Darwinism does, that we are products of our genes, then you’re saying that the dramatic differences between us and chimpanzees are due to two percent of our genes… The problem is that the so-called body-building genes are in the ninety-eight percent. The two percent of genes that are different are really rather trivial genes that have little to do with anatomy. So the supposed similarity of human and chimpanzee DNA is a problem for neo-Darwinism right there.” [p.54]

This passage implies that Wells rejects not only evolution, but genetics itself, which would put him well on the way to rejecting every discovery in biology in the last several hundred years. What explanation is he proposing for the differences between humans and chimps if he doesn’t think it’s due to genes? Do tiny angels with hammer and chisel reshape human embryos in the womb?

That aside, the evolutionary explanation neatly accounts for this supposed difficulty. Humans and chimps, after all, have the same body parts in the same basic arrangement. Our “body-building” genes don’t need to be much different. What is different is the genetic master switches, the developmental program, which has been altered to emphasize certain features and reduce others. Indeed, it’s widely understood that many of the differences between human and chimp stem from a developmental principle called neoteny: the retention of juvenile features into adulthood. To put it another way, humans look a lot like larger versions of baby chimps. This is most apparent if you look at our skulls:

Neoteny in humans

Top row: A fetal, infant, and adult chimpanzee skull. Bottom row: Fetal and adult human skull. Note how the adult human strongly resembles the infant chimp.

The final card Wells has to play is the one that creationists always use to explain away homology, the “common design” argument.

“A designer might very well decide to use common building materials to create different organisms, just as builders use the same materials – steel girders, rivets, and so forth – to build different bridges that end up looking very dissimilar from one another.” [p.55]

The flaw in this argument is that, although it can explain isolated similarities on an ad hoc basis, it cannot explain the overall pattern of similarities we see in living things. Designers, particularly omnipotent ones, are not constrained by past history in their work. They are not limited to variations or elaborations on designs they’ve already produced. They can borrow useful designs from anywhere and incorporate them into their plans.

But when we observe life on Earth, we don’t see this kind of mix-and-match planning. We don’t see dolphins with gills, bats with feathers, and so on. Instead, what we see are organisms whose adaptations apparently are constrained by past history. The mammal five-finger pattern is a clear example: it has no obvious explanation under common design (how would “common building materials” explain why a designer chose to repeat a pattern with no apparent purpose?). But it’s just what we’d expect if mammals were all descended from a common ancestor with five fingers.

As the old saying goes, the more things change, the more they stay the same. That slogan excellently summarizes the principle of homology. Even though the bodies of living creatures have changed dramatically to adapt to different environments, they still retain the deep similarities that point to their common descent from ancient ancestors.

Other posts in this series:

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  • Reginald Selkirk

    Nicely done.

    “A designer might very well decide…”

    Or a designer might very well decide to do the exact opposite. If one accepts an omnipotent designer, there are absolutely no constraints. But if a hypothesis explains everything, it explains nothing. It would be very curious if a designer chose only to do things consistent with the appearance of evolution.

  • penn

    Did you know that Albert Michelson and Edward Morley of the famous Michelson-Morley experiment that showed that the speed of light is constant and is used in support of Einstein’s relativity, did not actually accept relativity at the time of the experiment?

    OMG! Scandal!

    Seriously, the entire history of science is filled with people finding out facts that require new theories to explain. If the new theories can’t explain the old facts then what good are they? Wells simply cannot be ignorant of this fact.

  • 2-D Man

    I was going to say roughly the same thing, penn.

    Y’see the shining of the sun was first noticed by people who were not fusionists, therefore fusion most definitely does not power the sun!

  • Reginald Selkirk

    Did you know that Albert Michelson and Edward Morley…

    That reminds me of Creationists trotting out lists of scientists who were Creationists – which include people who died before Darwin even published.
    recent example

  • http://uncyclopedia.wikia.com/wiki/User:Modusoperandi Modusoperandi

    Holy crap! Duane Gish is on there? Wow. Colour me surprised. AND Henry Morris too?!

    Hold on. Now, I’m not big on the Arguments from Collective Ignorance (Argumentum Collectum Ignoris), but if that many people who have no idea what they’re talking about believe that the world is 6k, I’m convinced. I’m a YEC now. Yup. Time to chip the Darwin fish off the trunklid. Did you know that no one has found a so-called transitional fossil? Ever. True story. And what good is half an eye, anyway?

  • Alex Weaver

    So if I understand correctly, the “eyeless” gene, and therefore the two-main-eyes body plan, predates the deuterostome-protostome split.

    Should we call it “eyespotless” perhaps?

  • M.

    Ebon – do you know the source of the second (Neoteny) image? I have a perfect use for it, but in a forum that requires source citation.

  • http://www.ateosmexicanos.com/portal/ Juan Felipe

    Aside from the classic mammal limbs illustration, what are other good examples of homology, ebon?

  • Paul

    Found the second image here, with 2 photos attributed to “a 1926 study by the German anthropologist Adolf Naef”. Attribution for the center image (the one Ebon used) is less clear, and could be the same study or the person who put together the above page.

  • Leum

    Also relevant to this discussion are Hox genes. These are genes that play a role in the creation of homology, and are similar even between highly dissimilar animal species.

  • http://spaninquis.wordpress.com/ Spanish Inquisitor

    …he,[Wells] unlike the vast majority of creationists, has a legitimate degree in biology.

    Didn’t you say in an earlier post that Wells obtained his degree for the sole purpose of becoming a Creationist, in order to refute Evolution? If so, can’t one argue that his degree is not “legitimate”? Certainly, he did not go into the academic world with the open mind necessary to learn. This could explain why his knowledge seems so…stunted. He closed his mind, because he really didn’t want to learn something that would refute his predisposition. He simply went through the motions of getting a degree.

    He’s not a legitimate biologist by his own admission.

  • http://www.patheos.com/blogs/daylightatheism Ebonmuse

    The image comparing human and chimp skulls is one I found in several different versions on the web. I think, but can’t be certain, that I first saw it in Philip Kitcher’s Abusing Science: The Case Against Creationism.

  • Leum

    Spanish Inquisitor: I’m of the opinion, and I may be a minority, that if someone can successfully report what is believed by the scientific community, do research as though they agree with scientific principles, and while doing so meet the requirements for a degree in science anywhere from an Associate to a PhD, that their degree is entirely legitimate. There’s no way to be able to successful parrot science at that level if you don’t understand it, and it’s entirely acceptable for that person to still disagree with what they understand. Science shouldn’t be about beliefs; it should be about the ability to use the scientific method and the principles derived from it to produce meaningful interpretations of data.

  • Stephen P

    Wells’ degree is legitimate in the sense that it comes from a legitimate university rather than from a diploma mill.

    But as Ebonmuse points out, it’s a double-edged sword. It potentially gives him some credibility when arguing points at the fringe of science. But when he gets basic, well-established biology wrong he has no excuse: he is clearly lying.

  • Scotlyn

    Alex:

    the deuterostome-protostome split.

    I never heard about that one. It’s so hard to keep up with the goings on in these cults!

  • Jormungund

    Not to be a nit picker: but when I learned about neoteny in a university physical anthropology course, the “human’s are like infant chimps” idea was used as an example of what is NOT neoteny. Sure, human skulls look like young chimp skulls. No, that doesn’t me we are retaining juvenile chimp features. Our skulls are they way the are because of hypermorphosis. Our skulls form by extending growth of certain regions beyond what a chimp would grow. I believe that it was McNamara and McKinney’s research that discredited this hypothesis.
    Neoteny is real, but this example isn’t.

  • Alex, FCD

    I never heard about that one. It’s so hard to keep up with the goings on in these cults!

    There was a scriptural dispute. The deuterostomes believe that one should develop ass-first, where the proterostomes feel that this ontogeny is ass-backwards.

  • Thumpalumpacus

    Aside from the classic mammal limbs illustration, what are other good examples of homology, ebon?

    Comment #8 by: Juan Felipe

    Gill-bones and mandibles. Brain architecture.

  • http://www.patheos.com/blogs/daylightatheism Ebonmuse

    Aside from the classic mammal limbs illustration, what are other good examples of homology, ebon?

    Another good example is the human appendix, which is homologous to the cecum, a digestive organ used by herbivores to store symbiotic bacteria that help them digest cellulose.

  • Scotlyn

    Alex – @#17 – So glad I had just swallowed my coffee before I read that!!

  • http://www.patheos.com/blogs/daylightatheism Ebonmuse

    On Jormungund’s comment #16:

    Neoteny is real, but this example isn’t.

    Neoteny is obviously not the only process involved in turning chimps into humans, but I stand by my argument. See:

    Penin X, Berge C, Baylac M. “Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis.” Am J Phys Anthropol. 2002 May;118(1):50-62. (Abstract)

    We used the skulls of 41 Homo sapiens and 50 Pan troglodytes at various stages of growth. The Procrustes superimposition of all specimens was completed by statistical procedures (principal component analysis, multivariate regression, and discriminant function) to calculate separately size-related shape changes (allometry common to chimpanzees and humans), and interspecific shape differences (discriminant function). The results confirm the neotenic theory of the human skull…

    At the end of growth, the adult skull in humans reaches an allometric shape (size-related shape) which is equivalent to that of juvenile chimpanzees with no permanent teeth, and a size which is equivalent to that of adult chimpanzees.

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  • El t

    There is a novel, “After Many a Summer dies the Swan” by Aldous Huxley. In it an eccentric English nobleman and his wife take an elixir which lengthens their lives far beyond the normal range, but it also reverses the neoteny that has been a hallmark of human evolution for many millions of years. The result is that this unfortunate couple eventually develop into brutish ape-like creatures. A clever and satirical look at neoteny in the human species. The late popular science writer Stephen Jay Gould also gives impressive lists of the many similarities shared between humans and fetal and juvenile apes.

  • http://www.thewarfareismental.info cl

    Ebonmuse,

    Why conflate dissent with dishonesty? I see religious people make this mistake all the time when they assume atheists simply don’t believe because they are moral scoundrels or something similar. Are you seriously beyond even entertaining the possibility that you might be wrong, or that you might be the one misunderstanding Wells? I’d be more impressed if you invited Wells to respond, because I bet he’d explain his arguments quite differently than you have.

    ..the fact that both humans and dolphins have five finger bones (in dolphins, buried in their fins) is an example of homology, because no adaptive necessity that we know of would compel such a similarity of structure.

    Well, I agree that the pentadactyl limb design dolphins and humans share is an example of homology. I disagree that such is an example of homology “because no adaptive necessity that we know of would compel such a similarity of structure,” but hold that thought for a second.

    As with the similarities in vertebrate embryos, the homology among living creatures is an observation.

    Correct…

    Evolution is an explanation for that observation,

    Yet, you just conceded that no adaptive pressure we know of would compel homologous resemblance, and adaptive pressures drive evolution, so it seems to me you need to refine the argument.

    Designers, particularly omnipotent ones, are not constrained by past history in their work. They are not limited to variations or elaborations on designs they’ve already produced.

    Why must homologous resemblance be evidence of limitation or constraint? Your rebuttal to the “common-design” argument misses the mark because its conclusion does not flow from its premise. The phenomenon of homologous resemblance accompanied by differentiation in function supports the argument from special creation, with nothing more than an analogy from computer science and a quick reference to scripture. Any programmer worth their money knows to write a function for chunks of code that demand iteration. In doing so, the programmer enjoys the resourcefulness of simply calling the function rather than retyping the entire sequence of code, which is an enormous waste of time and also invites a large margin of error. This might be trivial if we’re writing a simple script that spits an image to a browser upon refresh, but the amount of code needed to create even a simple living cell is immensely more complicated (I am not saying ‘irreducibly complex’). If you as an all-powerful, creative being decided to create a different type or kind, would you want to rewrite the necessary genetic codes from scratch? Or would you create an autonomous function that simply copies and tweaks existing code?

    Even though the bodies of living creatures have changed dramatically to adapt to different environments, they still retain the deep similarities that point to their common descent from ancient ancestors.

    Correct, yet moot. Nothing in the concept of LUCA conflicts with the idea that an intelligent being created the current panoply of life.

  • Alex, FCD

    …you just conceded that no adaptive pressure we know of would compel homologous resemblance, and adaptive pressures drive evolution, so it seems to me you need to refine the argument.

    If adaptive pressures were the only constraints on evolution, then you would be correct. However, natural selection also has the important constraint that it has to work with the lineage that it’s given; it can’t double back or redesign parts from scratch. The fact that dolphins have five metacarpals rather than two or eleven is not the result of selection amongst competing early dolphin forms with different numbers of fingers, but the fact that dolphins are descended from pentadactyl ancestors. This is what’s meant by ‘there’s no adaptive reason for dolphins to have five fingers’.

    Why must homologous resemblance be evidence of limitation or constraint? [Makes an analogy computer programming]

    The difference is that computer programmers don’t call up functions that they don’t need, and they can call up any function that they like. If somebody were programming a dolphin, they wouldn’t say “I need a fin, so I’m going to call up the pentadactyl limb function and force it to be fin-like with an awkward kluge”, they would just call up any of the perfectly good fin functions that they already coded when they were working on Fish 1.0. An even better example of this is ostrich wings. Ostrich wings are really well-adapted to flight, which they can’t do because they’re stuck to ostriches. Ostriches use them to balance when running and in courtship displays. To switch metaphors for a bit: giving ostriches beautiful bird wings to use for balance and rudimentary communication is like buying a new MacBook Pro and using it to drive nails. However, I’m probably just tiring out my fingers because:

    Nothing in the concept of LUCA conflicts with the idea that an intelligent being created the current panoply of life.

    As has been pointed out before: no possible observation conflicts with the idea that an intelligent being created the current panoply of life, provided that we make him* capricious enough. The idea is entirely immune to falsification.

    *And yes, in this context, it is nearly always a ‘him’.

  • http://www.rationalitynow.com Dan Gilbert

    Fascinating stuff! The more I learn about evolutionary theory, the more beautiful and wondrous it becomes to me… and the more interesting and logical it becomes.

    Thanks for posting this. Great info!


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