Evolutionists are not irrational. Their argument that evolution must be a fact is perfectly valid. It entails religious premises, but given those premises, the conclusion follows. Therefore problems with the scientific evidence are inconsequential. When the evidence contradicts the theory (as it often does), they just patch the theory. And there are a great many patches holding together evolutionary theory. Sometimes there are patches on top of patches. One problem that has used up several patches is the sudden appearance of new forms in the fossil record. How could such rapid appearance occur?
Darwin's confidant and supporter Thomas Huxley likened such rapid appearance of new species to a barrel that is filled rapidly with apples. Then it takes longer to fill the remaining spaces with pebbles, sand and finally water. So like the barrel, environments are abruptly filled with new species, and then modifications are added at a slower pace.
More recent explanations are more technical-sounding but no less reliant on speculation. Steven Stanley compared it to the introduction of bacteria croppers which prey on dominant species which previously had suppressed diversity. J. J. Sepkoski compared it to rapid growth of bacterial populations in a virgin petry dish. Were the Precambrian oceans a virgin ecosystem with the raw materials of oxygen and food supplied by ancient bacteria? Geneticist Steve Jones wondered if the Cambrian explosion reflected some crucial change in DNA--life’s genetic material. “Might a great burst of genetic creativity,” asked Jones, “have driven a Cambrian Genesis and given birth to the modern world?”
Now, a new paper suggests that microRNAs did the trick by increasing genic precision. It is yet another just-so story motivated by the non scientific belief that evolution is a fact. If evolution is a fact, then we merely need to explain it, no matter how absurd are the explanations.