By Brad Haugaard
In his classic work, The Origin of Species, Charles Darwin does an admirable job of documenting that plants and animals can change. He does this in excruciating detail, examining everything from cattle to pigeons, and proving beyond anybody's ability to doubt that changes to plant and animal life can be brought about not only by human breeding, but also by what you might call natural breeding, or "natural selection," as Darwin calls it. His evidence was simply overwhelming.
But what he proves is what nobody ever doubted. Think of all the varieties of dogs, from Chihuahuas to St. Bernards, or think of all the kinds of people there are. Of course species vary! As Darwin himself says, "Amongst organic beings in a state of nature there is some individual variability; indeed I am not aware that this has ever been disputed."
Nevertheless, if this examination of variability is just Exhibit A, it is a powerful start, at least if Exhibit B is equally persuasive. But it isn't. In fact, it would be difficult to say that Exhibit B exists. The next logical step would have been to demonstrate that natural selection has actually resulted in complete changes of species. He could have done this by documenting a few of the myriad of step-by-step fossils that he predicted would be necessary to bridge the species, or by showing that human breeding efforts had resulted in a species-to-species change.
He doesn't do this. In fact, he wasn't able to do this, which is why he quite properly called his proposal a "theory." What he does instead is provide several chapters in which he explains why he can't provide the evidence. He contends that the geological record is incomplete, so the fossils that would prove his case are missing; he says that evolution proceeds too slowly to see, so presumably, it is too slow to test by breeding; and he calls into question what exactly constitutes a species.
He doesn't completely ignore examples, but the best he can do is to speculate. He suggests, for example, that the tapir may have evolved into the horse, that something like a lemur may have become a bat, and, rather oddly, that bears (or something like bears) which swam through the water with their mouths open, may have been the ancestors of whales.
While Darwin made the best case for evolution that he could, I ended up thinking that the evidence he presented did not answer the main question: Can life evolve from a single cell into trees and elephants and kangaroos and people, or can it just evolve from Chihuahuas into St. Bernards?
Maybe a good analogy is a rubber band. Darwin clearly showed that life is flexible, like a rubber band. But can you stretch a rubber band forever? I don't think he proved that you can.