Jonathan Wells and Homology

This is the third and last of my answers to Jonathan Wells’ 10 unanswerable questions for evolutionists.

Question 3: Homology.

Wells: Why do textbooks define homology as similarity due to common ancestry, then claim that it is evidence for common ancestry — a circular argument masquerading as scientific evidence?

This question stems from confusion on Wells’ part between how something is defined and how it is recognized, which are two quite different things. Homology is indeed defined as similarity due to common ancestry. But we don’t just label any similarity a homology and call it evidence for common ancestry. That would indeed be circular. What we really do is quite different. Similarity between the characteristics of two organisms is an observation. If the similarity is sufficiently detailed (“both are big” or “both are green” won’t do) we consider it a candidate for homology.

Homologies can be tested to some degree by predicting that the characters will be similar in ways we haven’t yet checked. For example, if we propose that similar-looking bones in two animals are homologous, we might predict that they would arise from similar precursors in the embryo, have similar spatial relationships to other bones in the organism, and have their development influenced by similar genes. And this is commonly the case.

But the main way of testing candidate homologies is by congruence with other proposed homologies. By congruence we mean that the two characters can plausibly belong to the same history. If the history of life looks like a tree, with species related by branching from common ancestors, then all true homologies should fit that tree; that is, each homology should arise once and only once on the tree. If a large number of functionally and genetically independent candidate homologies fit the same evolutionary tree, we can infer both that the candidates really are homologies and that the tree reflects a real evolutionary history.

And in fact that’s what we commonly find. Mammals, for example, are inferred to descend from a common ancestor because they all have hair, mammary glands, and other more obscure characteristics like seven neckbones and three earbones. All these characteristics go together: mammals have all of them and no other animals have any of them. Further, other characters support consistent groupings within mammals, and groupings within those groupings. Within most of life, groups are organized in a very special way called a nested hierarchy. In a nested hierarchy, every group is related to every other group in one of two ways: either one group entirely contained within the other (as in a below), or they share no members at all (as in b below). No two groups can partially overlap (as in c below).

What we see if we try to organize species using candidate homologies is that groups organized according to different characters fit together like a and b, but not c, so we get a pattern like this:

Why should these and many other characters all go together in this consistent way? Evolutionary biology explains these characters as homologies, all evolved on a single tree of descent, like this:

Wells gives no alternative explanation for such patterns, and indeed they are hard to explain in any other way than as reflections of an evolutionary history. Wells has it all wrong. Homology isn’t a circular argument, it’s a branching tree of evidence.

 

 

77 thoughts on “Jonathan Wells and Homology

  1. Erik,

    Let me suggest that you are completely failing to understand what Darwin meant. I’ve shown you what he meant, quoting from the Origin itself. And why is what Darwin meant even relevant to modern evolutionary biology? He’s not the seal of the prophets or anything like that. How is this at all relevant to what homology is and whether we can infer phylogeny?

  2. John Harshman: And why is what Darwin meant even relevant to modern evolutionary biology?

    Deal.

    (Because to bury the originator of the modern evolutionary biology is to bury the modern evolutionary biology. If even Darwin didn’t get evolution right, then nobody can.)

  3. Erik: Deal.

    I’m afraid you’re treating Darwin as if he were the seal of the prophets. He was wrong about a number of things. We know much more than he did. Science progresses, you know. So what you’re saying is absurd.

    And he was actually right on the point we’re talking about now, though you seem unable to see that.

  4. John Harshman,

    Thats a error. Yes German brought forth english etc but no indo european did not bring forth german.
    Or rather the evidence for it is entirely based on likeness in words etc.
    Instead there was one language, at Babel, and it was just a sudden twist on big identity groups to be different from others. No evolution.
    no reason to see a indo european language.
    the reasons for why they are related does not demand common decent mechanism as it does in a german family relative to english.
    Its just reasoning from here back to there without allowing other options.

  5. Robert Byers: Yes German brought forth english etc but no indo european did not bring forth german.
    Or rather the evidence for it is entirely based on likeness in words etc.
    Instead there was one language, at Babel, and it was just a sudden twist on big identity groups to be different from others. No evolution.
    no reason to see a indo european language.

    Erik, observe your doppelganger, differing only in that he’s ignorant of linguistics as well as biology.

  6. Allan Miller: Oh, like organisms need like DNA, don’cha know.

    When a species gives birth to another species, what exactly is it that corresponds to the zygote in that process?

  7. Erik: Neckbones and other characters were a much clearer example.

    LoL!

    It’s like a shell game. Follow the pea.

  8. John Harshman: Simple enough. By the standard method of science, which is to ask whether one hypothesis explains the data much better than some other hypothesis. If the data show a strongly nested hierarchical pattern, we infer that the similarities are due to common descent, because we know that common descent would be expected to produce such a pattern and we can’t think of anything else that would be expected to do so. Do you?

    John’s playing his games again. Trying to shift the burden of proof. Some things just never change. So we have hypothesis J (the one John likes), and John and cohorts have compared it against what other hypotheses, exactly?

  9. John Harshman: So your basic problem is that you have no idea of how science works.

    We know that the “science” of evolutionary biology doesn’t work like the science of physics. So we seem to be a step ahead.

  10. The similarities we use to classify living things are called “homologies,” sometimes defined as features that are similar in structure and/or position but which may perform different functions.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 310-311). Discovery Institute Press. Kindle Edition.

    Owen and others reasoned that analogy suggests independent adaptation to external conditions, while homology suggests deeper morphological (anatomical) affinities, so homology is a better guide to classification than analogy.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 314-316). Discovery Institute Press. Kindle Edition.

    Owen attributed homology to construction on a common plan, but Charles Darwin argued that the best explanation for homology is descent from a common ancestor. In The Origin of Species he wrote that genealogy is “the only known cause of the similarity of organic beings.”1 Thus “I view all beings not as special creations, but as the lineal descendants of some few beings” that lived in the distant past.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 322-326). Discovery Institute Press. Kindle Edition.

  11. DESPITE THE fact that ancestor-descendant relationships cannot be empirically recovered from fossils, the modern biological literature is full of evolutionary trees—called “phylogenetic” trees—that supposedly show such relationships. The trees are typically accompanied by stories of how earlier organisms evolved into later ones. But phylogenetic trees don’t require ancestors. In fact, they don’t even require organisms.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 425-428). Discovery Institute Press. Kindle Edition.

  12. John Harshman: So your basic problem is that you have no idea of how science works. All science works the way I have just described.

    Really, wow…there is a way “science” works, cool!

    Political science? Sports science? Science of sleep? Science of hypnosis? The science of love?

    Please tell me again where you described this, this is amazing news. The science of science!

  13. Erik: (Because to bury the originator of the modern evolutionary biology is to bury the modern evolutionary biology. If even Darwin didn’t get evolution right, then nobody can.)

    Sir Isaac Newton got some things wrong

  14. Erik: Was gravity among those things?

    He predicted the effects correctly for the most part without knowing exactly how it worked.

  15. Mung,

    When a species gives birth to another species, what exactly is it that corresponds to the zygote in that process?

    When a bacterium, through fission, results in two descendant bacteria, what exactly corresponds to the zygote in that process?

  16. Allan Miller: When a bacterium, through fission, results in two descendant bacteria, what exactly corresponds to the zygote in that process?

    Absolutely nothing. The ball’s back in your court.

  17. There is no element of time or ancestral relationship in a cladogram. An evolutionary biologist may assert that the outgroup and ingroup are related through ancestry and descent, but there is nothing in a cladogram itself that requires such a relationship. Ancestors and transitional forms are left to the imagination.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 451-453). Discovery Institute Press. Kindle Edition.

    The old-fashioned evolutionary trees that used to adorn biology textbooks have now been largely replaced by cladograms. Nevertheless, most textbooks still mislead students into believing that cladograms are ancestor-descendant diagrams.

    Wells, Jonathan. Zombie Science: More Icons of Evolution (Kindle Locations 466-468). Discovery Institute Press. Kindle Edition.

  18. John Harshman: Erik, observe your doppelganger, differing only in that he’s ignorant of linguistics as well as biology.

    doplleganger seems a foreign word , never heard it before, but i’m not ignorant of linguistics, or its not revealed by why i revealed about this talk on linguistics.

    The bible said all spoke the same language. At babel everyone was divided into family groups. then god confused, put a spin, on the language.
    Just a spin. not whole new languages.
    so it would be, if this was so, that all languages could show likeness.
    Yet the indo -european languages did not evolve from a common original language but are only twists off the great parent language. So the indo-eur group just reflects a closer group. its the Japhet group. A son of noah and shown in the table of nations in genesis.
    Again this is a classic case for insisting there is only one option.
    BECAUSE there are other options for likeness, other hen common descent, then subjects like homology are wrong to define homology as from common descent.
    Then use likeness to say they proved common descent like Wells smartly pointed out.
    Homology is only about likeness and not about why its likeness.
    Please correct the textbooks from the evolution bias and incompetent scholarship.
    Homology back to the people.

  19. Mung,

    Absolutely nothing. The ball’s back in your court.

    What? It just whizzed off the edge of your racket into the bushes. You think that the only sense in which something can have ancestors or descendants is by mating and forming a zygote? That’s silly. New balls please.

  20. Robert Byers: Please correct the textbooks from the evolution bias and incompetent scholarship.
    Homology back to the people.

    Why don’t you start the ball rolling by showing what such a correction would look like. Why don’t you write chapter one of the new textbooks? Or is it that someone else, as usual for you lot, has to do the actual work?

  21. OMagain: Why don’t you start the ball rolling by showing what such a correction would look like. Why don’t you write chapter one of the new textbooks? Or is it that someone else, as usual for you lot, has to do the actual work?

    The trouble with that is, he just might do it. Not at all well, of course, but he has written a fair amount about how marsupials are merely pouched versions of placentals. Even creationists won’t swallow it, but he seems never to doubt himself, no matter how wrong.

    He won’t do the science, of course (doesn’t understand it), but I wouldn’t encourage him to write nonsense. He can do that.

    Glen Davidson

  22. OMagain: Why don’t you start the ball rolling by showing what such a correction would look like. Why don’t you write chapter one of the new textbooks? Or is it that someone else, as usual for you lot, has to do the actual work?

    i’m the thinker. writing is another skill.
    Anyways i’m making a excellent case for why everyone should change the textbooks.
    they are clearly wrong on homology. Well’s is completly right and is writing about it and maybe will be a agent of change in biology textbooks.
    Homology is just about bodyplans/traits looking alike in different creatures.
    So why is the definition of homology based on common descent??
    A definition of homology must be independent of any hypothesis of its origin.
    This is the law of science definition!!
    Then to rub salt in the wound.
    They use , in contention on origins of homology, the definition as proof for the claim of homology coming from common descent. oh brother.
    Maybe i should write the biology books..!!?

  23. GlenDavidson: The trouble with that is, he just might do it.Not at all well, of course, but he has written a fair amount about how marsupials are merely pouched versions of placentals.Even creationists won’t swallow it, but he seems never to doubt himself, no matter how wrong.

    He won’t do the science, of course (doesn’t understand it), but I wouldn’t encourage him to write nonsense.He can do that.

    Glen Davidson

    Creationists aren’t right about everything?!
    I don’t doubt I’m right but its from analysis and study.(actually lots of humanity don’t doubt themselves and is a problem)
    I understand the “science concept”. Its just people thinking and doing a better or worse job.

    By the way marsupial convergent evolutionists claims relative to placentals is a issue for homology based on common descent.
    Body plans/traits in this case contradict what they do otherwise.

    .

  24. Robert Byers: By the way marsupial convergent evolutionists claims relative to placentals is a issue for homology based on common descent.
    Body plans/traits in this case contradict what they do otherwise.

    “what they do otherwise” suggests that all (or most) non-marsupial mammals provide body plans/traits which fit well into common descent homology. I would strongly agree with you on this point if no other;-)

  25. Robert Byers: Yes German brought forth english etc but no indo european did not bring forth german. Or rather the evidence for it is entirely based on likeness in words etc.

    And if Comparative Linguists starting considering “likeness in words” between languages as objective evidence, where would we be?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.