The one big reason that ‘common design’ is a bad argument for creationism

Common ancestry? Very possible. Common design? Eh, not so much. (Public domain photo.)

One of the strongest and most broadly observable planks of evidence for evolution by common descent rests in the homology — a fancy, five-dollar word for “similarity” — observed in the animal kingdom, both in comparative anatomy and genetics.

In basic terms, the theory of evolution depends on similarities. It predicts that species branch off from common ancestors, but because this occurs through a slow, gradual process, we should observe a vast number of similar traits — both genetically and anatomically — in closely related species (i.e., ones that branched off more recently), such as chimpanzees and humans.

Evolution works too slowly for large numbers of traits to be changed simultaneously at a branching event. A fish will never beget a chicken; these things take time. So scientists look for commonalities; they find the stem that leads back to the stalk that leads back to the twig that leads back to the stick that leads back to the branch that, eventually, takes them all the way back to the tree.

If we did not find such similarities between closely related species, it would falsify evolution immediately. But, of course, we do. For example, humans share almost 100 percent of our bone structure, and roughly 96 percent of our genome, with chimps. That’s a pretty high degree of homology. Going further back, we find that humans — like all mammals — have hair, mammary glands and a single temporal opening in our skulls. And going even further, way, way back, we — like all life — are carbon-based and carry DNA within our cells.

I hope this simple explanation demonstrates — despite the anti-evolutionists who rail about the supposed conspiracies that rule “Academia” and desperately try to “prop up” their pet theory — how fragile the theory of evolution really is. If scientists ever discovered a single species that was fundamentally unlike any other, or even a species that was so wildly different from its closest relatives that it could not be explained by a gradual, stepwise process, the theory would crumble to the ground.

This discussion also illustrates how the scientific process operates. You start with the question — “Why does life bear seemingly hierarchical similarities?” — develop an explanation, then test that explanation through predictions, observation and experimentation. Evolution has great explanatory power in this regard, and it has been confirmed through repeated, independent tests in many different fields of inquiry, so it remains the prevailing theory.

But it is not the only explanation. There is another that is favored by anti-evolutionists, like the Discovery Institute’s Casey Luskin. Writing in response to the most recent “Cosmos” episode’s presentation of some of the genetic evidence for evolution, Luskin writes:

If not by “mindless evolution” and common ancestry, how can we explain the fact that genes in different organisms are so similar? Though Neil deGrasse Tyson never mentions it, a fully viable explanation or these functional genetic similarities is common design.

Intelligent agents often re-use functional components in different designs, which means common design is an equally good explanation for the very data — similar functional genes across different species — that Tyson cites in favor of common ancestry.

Interestingly — though the Disco Tute tries to distance itself from more openly religious groups like Answers in Genesis as much as possible, and vice versa — the “common design” argument is also used constantly by young-earth createvangelists. For example, AiG says in its “12 Arguments Evolutionists Should Avoid”:

Common body plans (homology), for example, do not prove common descent — that’s an assumption. A common Designer fits the evidence just as well, if not better.

I can’t really attempt to address the Disco Tute’s version of “common design,” since ID proponents’ definition of who or what the “intelligent designer” is — and how he/she/it works — is so vague and fluid it can refer to just about anyone or anything. But for those who openly admit that they believe “the Designer” can only be God, I can not only respond to the argument, but also point out that it is an exceptionally bad one.

Here’s why. Moving to the art world for just a second, let’s imagine that I was a critic analyzing two paintings: the “Mona Lisa” and the “Madonna of the Rocks.” And let’s say that I determined, based on the high degree of similarity in style and composition between the two works, that they were painted by the same artist (which is, of course, exactly the case).

So far, so good. But what if the next thing I suggested was that the same person who composed these two paintings was also responsible for every work of art that had ever been made — from the Venus of Willendorf to Beethoven’s Ninth — regardless of style, subject matter, materials used, date of composition or any other relevant details?

You’d probably think I’d gone insane. You can’t point to the similarities of two very similar things as proof that they came from the same artist, and then go on to suggest that the artist also made everything else — even things that are dissimilar in virtually every way.

Now, critics may respond, “Well, this is exactly what evolution does, though!” Except that it doesn’t. It’s true that evolution suggests humans share common ancestry, not just with closely related species like chimps and orangutans, but all other life — however, it also provides a predictable, testable and falsifiable model that explains exactly why some species look more similar, and others look less similar.

The alternative, “common design” theory has no such explanatory power. Why did God make this species similar to this other species? “No idea. That’s just the way he did it.” Why do these two species look so wildly different? “See above. God works in mysterious ways.” And so on.

But the problems go even further than this, because, while the theory of evolution is limited to living things, the theory of “common design” is not. Because the Christian common designer is the God who created, literally, the vast universe and everything in it, and “without him, nothing was made that has been made.”

So, to sum up: “Common design” suggests that the high degrees of similarity between humans and chimps suggest that the same designer created both. Fine. It’s not scientific (since supernatural forces lie outside the bounds of science), but I have no philosophical problems with the proposition. It makes sense.

“Common design” also suggests that the same designer created all living things. OK. Well, unlike evolution, this notion is not predictive or falsifiable or explanatory. But, like I said before, there are a few bare similarites shared by all life — despite its vast diversity. Perhaps I’d let it slide.

But then, “common design” also suggests that the same designer created and structured absolutely all matter in the universe, and that’s where the theory goes off the rails completely. Don’t get me wrong here: I’m a Christian. I believe that God made everything. But I don’t submit my belief in this matter as a scientific explanation for anatomical homology.

If similarity really were the mark of a common designer, and everything in the universe was specially created by the same designer, then we would expect to find the same level of similarity in every aspect of creation. Of course, we do not. We see in the universe humans and sturgeons and hippos and archaea and cyanobacteria and fungi and stars and quasars and galaxies and black holes and cosmic dust and dark matter and energy and plasma and magnetism and electricity and meteors and so much more — the only commonality being that they all exist in some form or fashion, which is not much to hang a theory on.

Now, it may still be true that God made everything (that’s what I believe), but if it is, similarity is obviously not his hallmark: Diversity is.

Which, to me, makes him look a whole lot more like the God of evolution than the God of “common design.”

Tyler Francke

  • Will

    “And going even further, way, way back, we — like all life — are carbon-based and carry DNA within our cell nuclei.”

    Not all life has nuclei. Eukaryotes do. An accurate sentence would be “And going even further, way, way back, we — like all life — are carbon-based and carry DNA within our cells.”

    There is also a grammatical error at “and then go on to the suggest that the artist also made everything else.” Either change “suggest” to “suggestion,” or remove the “the,” but splitting an infinitive with a hanging article is very weird.

    Otherwise, the article is quite good!

    • Right you are, in both instances. Thanks for the help, Will! Glad you liked the piece!

  • George

    Very good article! I am a philosopher and I absolutely enjoy the finesse you employ in bringing those two subjects to work together. 🙂

    • Wow, thanks, George! I really appreciate that! Glad you like it 🙂

  • John Wilkins

    I wish to cavil slightly: “homology” is not a fancy way of saying “similarity”. That is “homoplasy”. Homology is the identity of parts of organisms “under all forms and functions”, to paraphrase Richard Owen, who came up with the notion. Parts that do not resemble each other very much at all, like the malleus in reptiles that becomes the inner ear bone in mammals, can be homologous.

    • Grr, I knew somebody would knock me for that eventually! You’re right, I fudged the definition a bit. Thanks for the correction and the additional information 🙂

  • Larry Bunce

    Human desigers have limited resources, and often re-use solutions they have used before in solving problems. This often gives artists and composers a very recognizable style. Assigning human limitations to an Infinite Being may help personify God to us, but it diminishes God’s majesty. We can easily see defects in animal design: hard to reconcile with a Perfect Designer. Presumably God wouldn’t have bad days. How much more fantastic is God’s design for life to have set up the laws of chemistry so that self-replicating chemical reactions could become alive and pass on traits so that the defects we observe can be rectified in time, and so that life can adapt to its constantly changing environment.

    • Great points, Larry. Thanks! Always good to hear from you.

  • Paul Braterman

    The DI say “If not by “mindless evolution” and common ancestry, how can we explain the fact that genes in different organisms are so similar? Though Neil deGrasse Tyson never mentions it, a fully viable explanation or these functional genetic similarities is common design.”

    If DNA similarities reflected purposeful design similarities, we would expect parallel evolution (e.g. of marsupial and placental rodent-like mammals) to cause similarities of appearance and function. That does not happen, and for this reason alone, even without the others you mention, this purported explanation is not viable but stillborn.

  • Chiefley

    There is another asymmetry between the theory of evolution and the premise of design when it comes to the similarities in organisms. The basic premises of evolution predict a particular kind of pattern in the similarities and differences between organisms that evolved from a common ancestor. And it makes those predictions out of logical necessity, meaning that the pattern it predicts is inescapable from the way the premises work. In other words there can be no other outcome. This is what Tyler was alluding to when he said it ToE is fragile.

    Another term for fragility is that it takes predictive risk. In demanding such a precise and unique outcome (called a ‘prediction’ in science) in the relationship between evolved organisms it places itself at risk of being easily falsified if it is wrong. We rely on this property of falsifiability to judge between competing hypotheses based on failures in their predictions about nature. And so when science is evaluating whether a hypothesis is scientific or not, it looks to see how easy it would be to falsify the hypothesis if it is wrong. So we would ask the question for the theory of evolution,

    “What does the theory of evolution demand that we see in the relationship between evolving organisms (if it is true) and what does it forbid us to see in the relationship between evolving organism (if it is true)?”

    Consider the simple unconstrained premise of “common designer”. Try asking the same question:

    “What does the premise of “common designer” demand that we seen in the relationship between designed organisms (if it is true), and what does it forbid us to see in the relationship between designed organisms (if it is true)?”

    Notice that the same question about common designer is unanswerable. If you suggested something that we must see or must not see in designed organisms, you would then be asked to provide the logic for how that demand or that forbiddance comes about? You see, designers are free to do anything they want to do. They can design things that are very similar to each other or things that have no similarity to each other in any way.

    And this makes the notion of a common designer unfalsifiable. There is nothing we would see in nature that would refute the premise of design, as with design all things are possible. And where all things are possible, nothing is impossible. And where nothing is impossible, there are no tests you can run to rule it out.

    And this is why the premise of design is not accepted by the scientific community as a scientific hypothesis, as it cannot be tested.

    • Great points, @Chiefley:disqus! Thanks for taking the time to explain this!

  • sombodysdad

    Common design refers to Linnaean taxonomy and his archetypes. His nested hierarchy lays out the structure and the degree of similarity that should be expected.

    • Matthew Funke

      It seems to me that this is begging the question (or “circular reasoning”, if you prefer). Why does Linnaean taxonomy lay out the degree of similarity that should be expected? This is an interesting question, especially in light of the fact that the only known processes that specifically generated unique nested hierarchies are branching evolutionary processes — descent with modification.

      Separately-created things do not generally fit into nested hierarchies. For example, the cars, motorcycles, and trucks that Honda makes are designed by a single group of Honda engineers, but any attempt to sort them into a nested hierarchy eventually breaks down, because all defining characteristics in a group are not shared universally by members of that group. (A single radio model might appear in some trucks and some cars, for example. And even if you managed to impose some kind of scheme onto it, the scheme would be arbitrary — depending on whether you chose to sort by size or by color first, say. But the same nested hierarchy pops up for organisms whether you choose to sort by morphology or by genetics or by molecular biology. This argues strongly that the nested hierarchy is not illusory.)

      Interestingly, Linnaeus tried to classify minerals into a nested hierarchy after his success with organisms. He failed miserably, precisely because minerals are created separately and resist sorting into a nested hierarchy.

      So why would a Common Designer sort organisms into a hierarchy that is extremely atypical for separately-created things and also perfectly suited to common descent? Is the Common Designer just screwing around with us?

      • sombodysdad

        No, descent with modification does not produce nested hierarchies. Linnaean taxonomy is a nested hierarchy and doesn’t have anything to do with evolution. Transitional forms, by their very nature, would blur all lines of distinction between groups- nested hierarchies require distinct sets without any overlap..

        A common design is a great way to control your design. It prevents you from re-inventing things along the way.

        • Matthew Funke

          No, descent with modification does not produce nested hierarchies.

          Really? Students, teachers, and practitioners of linguistics, ancient manuscripts, epidemiology, phylogenetic analysis, parasitic virulence, bioinformatics, genetic programming, pharmaceuticals, pattern recognition, data mining, military strategy, enzyme creation, neural nets, and countless other disciplines would like to have a word with you.

          Simply saying “no” doesn’t prove anything when those who study how organizational patterns are formed know otherwise. Entire branches of analysis (e.g., linear regression analysis and analysis of variance) at use in literally hundreds of industries and fields of study are predicated on the notion that descent with modification produces nested hierarchies.

          In the face of human understanding and experience, it would seem to take a certain amount of hubris to stand there and just shake your head. I’m going to need a bit more than that.

          Transitional forms, by their very nature, would blur all lines of distinction between groups

          No, they wouldn’t. Think of family trees. Sure, some lines would be blurry — and in taxonomy, some lines are blurry. (Some grasses are really hard to tell apart, for example; at least ten percent of bird species are similar enough to produce fertile hybrids (citation below); and there are phenomena like ring species where determining boundaries can be tough.) But others are rather distinct, simply because the branches separated some time ago and have gone their separate ways, because ecological niches are not continuous, and because death and extinction go in only one direction. Hyperbole about “all lines of distinction” isn’t helping you here.

          Weiner, Jonathan. The Beak of the Finch: a story of evolution in our time. New York: Knopf, 1994. pp. 198-199

          Now, your turn: Why are some things that perform the same function very similar in some cases, but very different in others? For example, the wings of a bat, a bird, a pterosaur, and an insect are all very different from one another, but they accomplish much the same goal: Flight. Likewise, the fin of a fish, a dolphin, and a plesiosaur look very different from one another. Evolution not only predicts that you will find similarity in some places, but when you should expect which kind of similarity, and when you should expect which kind of difference. So far, life on Earth hasn’t run afoul of its predictions. Does the idea of a Common Designer, by itself, offer that kind of predictive power? Or does it have any explanation as to why these things look exactly as if they had evolved? Or does it offer any kind of reason for why a Common Designer would want to re-invent things some times, but not others?

          • sombodysdad

            Family trees do not produce a nested hierarchy. Just because nested hierarchies can be laid out as a branching tree doesn’t mean every branching diagram is a nested hierarchy.

            Again Linnaean Taxonomy is the observed nested hierarchy and it doesn’t have anything to do with evolution. The USArmy can be placed in a nested hierarchy and it also has nothing to do with evolution.

            http://evolution.berkeley.edu/evolibrary/article/evo_10

            Because the Linnaean system is not based on evolution, most biologists are switching to a classification system that reflects the organisms’ evolutionary history.

            Can you please reference this theory of evolution so we can see what it really predicts?

          • Matthew Funke

            Just because nested hierarchies can be laid out as a branching tree doesn’t mean every branching diagram is a nested hierarchy.

            When did I say that branching diagrams are only nested hierarchies? What exactly are you arguing, and whom are you arguing with?

            (One must also consider the consilience of the evidence. The nested hierarchy of life strongly argues for the correctness of evolution (as opposed to separate and instantaneous creation), but it is far from the only and far from the strongest evidence.)

            Can you please reference this theory of evolution so we can see what it really predicts?

            I’m not sure what you’re asking here. The taxonomy based on the theory of evolution is commonly referred to as the phylogenetic tree, if that helps. Are you trying to assert that Linnaean taxonomy is correct, and that the phylogenetic tree is not?

          • sombodysdad

            No, family trees do not produce a nested hierarchy. The parents do NOT consist of nor contain their children. With a nested hierarchy there is a superset that consists of and contains all subsets. The animal kingdom consists of and contains Phyla which consist of and contain Classes, which consist of and contain Orders and so on. Family trees are an example of a pecking order.

            Read this- http://www.botany.wisc.edu/allenlab/AllenLab/Hierarchy.html

            and this:

            http://www.mobot.org/plantscience/resbot/Repr/Add/Knox1998BJLS.pdf

            Regardless of what is eventually learned about the evolution of Clarkia/Heterogaura, the complex nature of evolutionary processes yields patterns that are more complex than can be represented by the simple hierarchical models of either monophyletic systematization or Linnaean classification. page 34, Eric B. Knox, “The use of hierarchies as organizational models in systematics”, Biological Journal of the Linnean Society, 63: 1–49, 1993

          • Matthew Funke

            The parents do NOT consist of nor contain their children. With a nested hierarchy there is a superset that consists of and contains all subsets.

            I think I was unclear about which sets one should regard in this case.

            In a family tree, the “sets” are not individuals represented by the tree nodes. (Individuals cannot be sets.) The sets are parental inheritances which are possessed by those individuals. As such, the parental inheritances of the children are subsets of the parental inheritances of their parents. The children cannot obtain parental inheritances from anything but the set of parental inheritances of their parents. The “superset” at the base of the tree (assuming one could go back far enough to find one) is the parental inheritances of the original parents. Which means that family trees are nested hierarchies.

            “The use of hierarchies as organizational models in systematics”

            Yes. All this quote is saying is that monophyletic systemization — e.g., Linnaean categorization — is not possible for the organisms under discussion because the categories are difficult to distinguish, which is because the continuum between organisms is hard to splice into distinct subsets — which, you’ll note, as indicated by the quote, Linnaean taxonomy is particularly ill-equipped to grapple with. This in no way contradicts the idea that a phylogenetic tree is an appropriate way to understand the descent of these organisms; it just means that we don’t yet know enough to set up the proper paraphyly for these organisms. It also does not indicate that the phylogenetic tree is not a nested hierarchy. (You’ll note that the phylogenetic tree is not monophyletic. It has monophyletic groups, which it calls “clades”, but it is not itself monophyletic.)

            Is it your contention that Linnaean taxonomy is correct, and that the phylogenetic tree is not?

          • sombodysdad

            That so wrong. Family trees are not nested hierarchies. You can even send an email to the experts I referenced and ask them.

            Phylogenetic trees are not nested hierarchies either. You have no idea what you are talking about.

          • “Nuh uh! You’re wrong! All the experts agree with me! You’re stupid! Waaaaah!”

          • Matthew Funke

            Family trees are not nested hierarchies.

            I admit my usage was unorthodox, and that I did not explain myself well. But if you consider it in terms of descent with modification, the structure is certainly there.

            Phylogenetic trees are not nested hierarchies either.

            If they were not, then Markov chains (and Markov mathematics generally) would not be applicable to them. Do you have evidence that this is the case?

            Is it your contention that Linnaean taxonomy is correct, and that the phylogenetic tree is not?