Fossil Horses and Directed Evolution

I'm teaching part of a course on Popular Scientific Misconceptions. In my section we'll be talking about the evolution/creationism controversy and part of the discussion involves analysis of the techniques used by Jonathan Wells to denigrate evolution in his book Icons of Evolution. One of the chapters is Fossil Horses and Directed Evolution.

For those of you who haven't read the book, the essential point is that scientists used to show the evolution of horses as a linear transformation from a small primitive horse-like creature to large modern horses. Over the years, this idea has been replaced by a branching representation where there are many different lineages, some of which have gone extinct. The history of this change is described in today's posting by Laelaps, which contains numerous examples of the figures and drawings that have been published over the years [The Branching Bush of Horse Evolution]. The most recent one is shown above. I'm posting the link here in part so my students will read it and it part so that everyone else will check it out. Laelaps has put a lot of work into the posting and he deserves the attention.

Jonathan Wells doesn't really object to the fact that the pattern of horse evolution has changed, although it does reinforce his point about scientific evidence being ephemeral. What upsets him is that the old version implied some direction to evolution and this, in turn, implies a director. According to Wells, the campaign by scientists to change the diagrams was only part of a larger, more sinister, goal.

The reason for their campaign, however, is more interesting than the horse icon itself. People used to regard the old icon as evidence that evolution was directed, either supernaturally or by internal vital forces. Neo-Darwinists now ridicule directed evolution as a myth, and cite new evidence that evolution is undirected.

But the doctrine of undirected evolution is philosophical, not empirical. It preceded all evidence for Darwin's theory, and it goes far beyond the evidence we now have. Like several other Darwinian claims we've seen, it is a concept masquerading as a neutral description of nature.

This is a strange line of reasoning. The original claim that horse evolution was directional surely falls into the same category that Wells criticizes. It must be philosophical, not empirical. Therefore, Wells should approve of scientists who refute the false evidence of directionality in order to remove a philosophical myth from the story of horse evolution. It seems logical that reverting to the null hyporthesis—no evidence of directionality—is preferable to promoting a mechanism that by Well's own admission might be supernatural.

That's not how Well's sees it.

Clearly, biology students are being taught materialistic philosophy in the guise of empirical science. Whatever one may think of materialistic philosophy, there is no doubt that it is being imposed on the evidence rather than inferred from it. And this is the real significance of neo-Darwinian efforts to reverse the picture of horse evolution. Although there are scientific issues involved, what really matters is the myth.

I'm looking at the tree of horse evolution. I don't see any evidence of directed evolution, do any of you? What's wrong with saying that there's no evidence of directed evolution; therefore we have to conclude that it wasn't directed?