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"Since it sounds as if he was looking at the modern species, I don't see how in the world he could have determined whether the genetic differences between them were due to "directed mutation", as he hypothesizes, or "directed *selection*" (a redundancy -- selection is, by definition, directed) of undirected mutations.

It seems that there would be no way to differentiate between the two processes, looking only at the end results."

That seems to be a valid observation to me. And I am trying to restate the explanation the evolutionary biologist gave as best I can, being some distance in time removed from watching that episode, which makes it difficult and makes me worry that I may get it wrong. But one thing I do remember is that he pointed out that, after the evolution of the various new species of grasses in distinct ecological regions, one of the common observations that could be made across these distinct ecological systems is that all of them possessed plant life, and his focus was on grasses, which left less of the energy available to them unused than before. He also went on to discuss the "megaflora" that was prevalent at the beginning of this process, when the principal ancestor of the new species of grasses was present, and then stated some hypotheses about why the "megaflora" did not survive, which essentially -- at least as best as I can restate this -- came down to the fact that they left too much energy within their ecological systems unused and were replaced by flora that made far more efficient use of that energy. And the disappearance of the "megaflora" he believed was the primary reason for the disappearance of the "megafauna" that has only been completed quite recently in the spanse of geologic time.

I have to confess that I am getting a little nervous discussing all of this in some detail because it has been quite a while since I saw this program, which I found fascinating, but the key point the evolutionary biologist made, and of this I am sure, is that his research suggested that natural selection may only explain the evolution of certain living organisms whose populations are under stress, while there may be an overall thrust to evolutionary development that is quite different.