Darwin said, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.” In his book, Darwin’s Black Box, Michael Behe, a biochemist, coined the term, “irreducible complexity” which, I believe, describes the kind of organ that Darwin had in mind. According to Behe, a system is irreducibly complex if it cannot function if even a single component is removed. After all, how could a system evolve gradually if it had to have every piece in place before it has any function at all?
Behe offered several examples of systems he said were irreducible complex. Critics, however, began to assail his examples – some more successfully than others – and attempted to show how such organs/systems could indeed have evolved gradually. In the end though, it is of no consequence because many evolutionists now argue that irreducible complexity is simply an argument from ignorance; just because we cannot imagine how such a system could have evolved, it does not prove the system didn’t evolve. So Darwin’s prediction of a complex organ disproving his theory is of no effect. No organ, no matter how complex, will ever fit the bill. It may still have evolved, we just don’t know how.
Another difficulty Darwin recognized with his theory was the lack of transitional forms in the fossil record. He said, “But, as by this theory innumerable transitional forms must have existed, why do we not find them embedded in countless numbers in the crust of the earth?” In another chapter he said, “But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed on the earth, be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.” Darwin, of course, blamed the imperfection of the fossil record for the lack of transitional forms. But now, 150 years and billions of fossils later, there is still a conspicuous lack of transitional forms: perhaps a hundred examples, not the countless numbers Darwin predicted should be there.
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Evolutionary biologist, J. B. S. Haldane, is credited with having said, “I will give up my belief in evolution if someone finds a fossil rabbit in the Precambrian.” That’s a pretty specific prediction. Evolutionists argue that animal life began as microbes, evolved into marine animals, then amphibians, later reptiles, and finally birds and mammals. If a rabbit (or any animal believed to have evolved later) were found in the earliest rock layers, it would be strong evidence the theory wasn’t true. But even before such an out of place fossil is found, evolutionists have started distancing themselves from the idea it would be evidence against their theory.
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There are other examples I could list but I think you get the point. To the true believers, evolution is true – let the evidence be damned! Nothing, no matter how contrary to earlier predictions, can dissuade devout evolutionists. The Theory of Evolution cannot be disproved as long as evolutionary scientist continuously move the goal posts.