Evolutionists say their idea is an obvious scientific fact and they have explained why over and over. In fact, the reasoning was already well established when Charles Darwin wrote Origin a hundred fifty years ago.
For instance, Darwin agreed that the perfection of the eye reminds us of the telescope which resulted from the highest of human intellect. Was it not right to conclude that the eye was also the product of a great intellect? This may seem the obvious answer but Darwin warned against it, for we should not “assume that the Creator works by intellectual powers like those of man.” Better to imagine the eye as the result of natural selection’s perfecting powers rather than having god too much involved in the world.
This warning against anthropomorphizing god came right out of the Enlightenment philosopher David Hume whose writings Darwin was well familiar with. It was a reaction to English natural theology that argued the world looks designed by god. Hume argued this made god out to be too much like His human creatures. For example, the natural theologians were fond of comparing the human body with machines such as clocks. No one doubts that a clock was designed, so why not the body as well? Hume used the problem of evil to negate this argument. Better to view god as distant and unknowable, and a creation that somehow arose on its own. Hume had no problem with god being infinitely powerful and wise, but he must also be transcendent and incomprehensible:
But as all perfection is entirely relative, we ought never to imagine that we comprehend the attributes of this divine being, or to suppose that his perfections have any analogy or likeness to the perfections of a human creature. Wisdom, thought, design, knowledge; these we justly ascribe to him; because these words are honorable among men, and we have no other language or other conceptions by which we can express our adoration of him. But let us beware, lest we think that our ideas anywise correspond to his perfections, or that his attributes have any resemblance to these qualities among men. He is infinitely superior to our limited view and comprehension; and is more the object of worship in the temple, than of disputation in the schools.
Far more lasting and influential than this anthropomorphic warning argument were the various arguments from evil, inefficiency and dysteleology. God would never have created this gritty world. These arguments had been developed and tested in the seventeenth and eighteenth centuries, and by Darwin’s day a foundation had been laid.
The predation and bloodshed in nature was an obvious example of a creation that seemed unbefitting of a loving god. But Darwin added a great many examples of nature’s designs that seemed to be better explained as a consequence of the blind interplay of natural laws than intelligent design.
Darwin presented these arguments throughout his book, with great conviction that they made his theory compelling. The first one appears at the end of the second chapter.
The first two chapters of Origin are on the topic of biological variation. In the first chapter Darwin discusses what breeders had learned (Variation Under Domestication) and in the second chapter he discusses biological variability in the wild (Variation Under Nature). The two chapters serve as a good summary of what was known at the time.
Darwin ends Chapter 2 with a section entitled Summary, but here he introduces a new, important idea. Yes, he summarizes what he has been discussing, but he provides a new, powerful interpretation:
In genera having more than the average number of species in any country, the species of these genera have more than the average number of varieties. In large genera the species are apt to be closely, but unequally, allied together, forming little clusters round other species. Species very closely allied to other species apparently have restricted ranges. In all these respects the species of large genera present a strong analogy with varieties. And we can clearly understand these analogies, if species once existed as varieties, and thus originated; whereas, these analogies are utterly inexplicable if species are independent creations.
Earlier in the chapter Darwin had made a few comments in passing about creationism, but nothing too significant. But here Darwin introduces the reader to the power behind his long argument. The pattern will repeat many times: long tedious passages followed by the powerful conclusion that nature’s evidence falsifies divine creation.
Don’t worry if you don’t completely follow the observations Darwin discusses in the above quote. Here’s what you need to understand. The take home message for evolutionists is that, as usual, there are no viable explanations other than evolution’s. The observations may not be fully understood under evolution, but under creation or design the story becomes downright impossible. As one of the twentieth century’s leading evolutionist Ernst Mayr wrote:
The greatest triumph of Darwinism is that the theory of natural selection, for 80 years after 1859 a minority opinion, is now the prevailing explanation of evolutionary change. It must be admitted, however, that it has achieved this position less by the amount of irrefutable proofs it has been able to present than by the default of all the opposing theories.
Or as Stephen Jay Gould put it:
Odd arrangements and funny solutions are the proof of evolution—paths that a sensible God would never tread but that a natural process, constrained by history, follows perforce. No one understood this better than Darwin. Ernst Mayr has shown how Darwin, in defending evolution, consistently turned to organic parts and geographic distributions that make the least sense.
Designs that make the least sense. They are one of the keys to understanding evolutionary thinking. In addition to the other arguments for why evolution is a fact, I examined this argument from dysteleology ten years ago in my book Darwin’s God: Evolution and the Problem of Evil, and others such as Paul Nelson had discussed it earlier. And so I was delighted to see this key evolutionary argument for the fact of evolution elaborated in the prestigious science journal, Proceedings of the National Academy of Sciences, a year ago.
The paper was written by philosopher Elliot Sober who for years had been analyzing evolution’s arguments in great detail. In that paper Sober points out that while one of the main objections to evolution, both when Origin was published and in the minds of many present-day Creationists, is the idea that species are separated from each other by walls. Darwin, Sober explains, overcame this with those designs that make the least sense:
Darwin thought he had strong evidence for common ancestry. This is enough to show that insuperable species boundaries (and insuperable boundaries between “kinds”) are a myth; if different species have a common ancestor, the lineages involved faced no such walls in their evolution. …
Adaptive similarities provide almost no evidence for common ancestry while similarities that are useless or deleterious provide strong evidence for common ancestry.
And why are useless or deleterious similarities so helpful? It is not because they raise the probability of common ancestry, but rather because they lower the probability of separate ancestry. In other words, the reason common descent is a no-brainer is that the alternative, separate ancestry, is extremely unlikely. Sober call this Darwin’s Principle.
I referred to this analysis and Sober’s paper in my previous posting and several evolutionists commented that I had misrepresented Sober. Here are some of their comments:
False. Sober said no such thing in that book. In fact, he said the opposite.
Darwin’s principle refers to the notion that traits that are not selectively advantageous are better evidence for common descent than are traits that are selectively advantageous. He says this in the context of comparing common descent to separate ancestry.
You are quite fond of misunderstanding Sober, aren’t you?
But in fact Sober did say such a thing. In the paper Sober clearly explains that Darwin’s Principle, which demonstrates species are not separated by insuperable boundaries, is based on the ratio of (i) the probability of evidence on common ancestry divided by (ii) the probability of evidence on separate ancestry. The key is that the argument is compelling not because of the former being high, but because of the latter being low. It is not a direct argument for common ancestry, but rather an argument against separate ancestry.
As Mayr and Gould explain above, evolution is a fact because design or creation is false, as demonstrated by so many inefficiencies and bad designs that make the least sense. Over and over, Darwin made arguments against divine creation as his proofs for evolution.
Sober explains this argument in great detail in his book Evidence and Evolution. Here is how he summarizes the paradox that common descent can be found to be a fact though the evidence is unlikely:
This last result provides a reminder of how important the contrastive framework is for evaluating evidence. It seems to offend against common sense to say that E is stronger evidence for the common-ancestry hypothesis the lower the value is of [the probability of E given the common-ancestry hypothesis]. This seems tantamount to saying that the evidence better supports a hypothesis the more miraculous the evidence would be if the hypothesis were true. Have we entered a Lewis Carroll world in which down is up? No, the point is that, in the models we have examined, the ratio [the probability of E given the common-ancestry hypothesis divided by the probability of E given the separate-ancestry hypothesis] goes up as [the probability of E given the common-ancestry hypothesis] goes down. … When the likelihoods of the two hypotheses are linked in this way, it is a point in favor of the common-ancestry hypothesis that it says that the evidence is very improbable. [Sober, Evidence and Evolution, p. 314]
In other words, it doesn’t matter that common descent is not a good theory. It must be true because the alternative is even worse.
As Sober explains his PNAS paper, the key is designs that are have low probability on separate ancestry. He gives examples such as gill slits in the human embryo and our tail bone, but Darwin used dozens of examples in addition to the Chapter 2 example above. These are classic examples used by evolutionists to show how compelling is evolution. The probability on common descent may be weak, but it must be true because the probability on design or creation is zero. Here are representative embryology and gill slit quotes from leading evolutionists:
How does God’s plan for humans and sharks require them to have almost identical embryos? [Douglas Futuyma, Science on Trial: The Case for Evolution, p. 48]
The passage through a fishlike stage by the embryos of the higher vertebrates is not explained by creation, but is readily accounted for as an evolutionary relic. [Tim Berra, Evolution and the Myth of Creationism, p. 22]
Now, we’re not absolutely sure why some species retain much of their evolutionary history during development. The “adding new stuff onto old” principle is just a hypothesis—and explanation for the facts of embryology. It’s hard to prove that it was easier for a developmental program to evolve one way rather than another. But the facts of embryology remain, and make sense only in light of evolution. [Jerry Coyne, Why Evolution is True, p. 78-9]
These evolutionary arguments certainly are powerful, but their power comes from their metaphysics. If the evolutionists are correct in their theological and philosophical premises then of course evolution is correct. Its likelihood would be a number divided by zero. And that is infinity. Granted the numerator may be small, but the denominator is zero. So it does not matter how ridiculous evolutionary theory is—it must be a fact.
All arguments for the fact of evolution are metaphysical. From the seventeenth century to today, evolutionists gain their tremendous confidence from their religious convictions. That doesn’t mean they are wrong, but it does place a tremendous burden on their metaphysics.
Sober does not approve of such metaphysics. Do they not make objective analysis impossible? In his book he first levels this criticism at creation and design. As I wrote in my review of his book:
Sober next presents what he takes to be a “devastating objection” to the design argument, first raised by David Hume in the eighteenth century. Sober argues that evolutionists should not make theological claims in proving evolution. Likewise, Sober finds the same defect in the design argument. For when Paley argued that the complexity of the eye implies a designer, was he not assuming knowledge of what God would design? [126, 141-147] Ultimately Sober concludes that creation and ID cannot even follow basic scientific protocol. 
And Sober agrees that evolutionists should not use such metaphysics as well. But Sober’s disapproval does not remedy the problem. As Gould and Mayr document, Darwin’s argument rested on the low probability of the alternative. This has not changed since Darwin and today, though evolutionists insist their idea is a scientific fact, it would be better characterized as a religious mandate. Every argument for why evolution is a fact is metaphysical. That doesn’t mean it is false, but it should not be thought of as a scientific fact.