These mutations must not have secondary harmful effects. Or there might be some seemingly unrelated and unforeseen effect that compromises survivability. A third faulty assumption is the often used analogy to artificial selection. But artificial selection works because it incorporates foresight and conscious purpose, the absence of which are the defining qualities of the blind watchmaker. In addition, artificial selection actually demonstrates the limits to change since an endpoint in the selection process is usually reached very quickly.
New types appear suddenly and change very little after their appearance.
The rarity of gradual change examples in the fossil record were revealed as the trade secret of paleontology by Steven J. Gould of Harvard. These are significant observations. Darwin predicted that there should be innumerable transitional forms between species. Not only that, but once these new forms have appeared, they remain relatively unchanged until the present day or until they become extinct. Some animals and plants have remained unchanged for literally hundreds of millions of years.