What does a “tree of life” purport to show? The obvious answer is a tree of life purports to show the pathways of common descent ASSUMING common descent occurred.
In the combox to a prior post a commenter who goes by wd400 writes:
That we can explain the data so well assuming a tree is evidence for common descent.
Wait just a second, you might say. Doesn’t a tree assume common descent rather than demonstrate it? Of course it does. wd400’s comment might just as well be re-cast as:
That we can explain the data so well assuming a tree is evidence for a tree.
We might be able to say that a tree of life diagram is consistent with common descent, if common descent were true. The diagram cannot be evidence for common descent for the simple reason that it assumes common descent to begin with.
In my last post I said this of Nick Matzke:
One wonders if his faith commitment to metaphysical naturalism renders him unable to see the circularity of his arguments, or if he does see it and just chooses to look the other way. My money is on the former. I think he is literally unable to grasp the obvious question begging that is immediately apparent to those who do not share his faith.
Here we see this same phenomenon again. I am all but certain that wd400 is perfectly sincere. He is not being intentionally provocative, intransigent or obtuse. It seems that it is almost literally impossible for him to see past his faith commitments to the circularity of his arguments.