A large number of different organisms had to be created supernaturally, because the processes of biological change are not capable of significant innovation. Let's consider first the processes that produce change in individual living things. Then we'll look at a process that produces change in populations of living things. Both creationists and evolutionists agree that mutations are the only source of new genes. These are genetic mistakes, errors in transmitting the information of inheritance from one generation to the next.
Mutations are almost always harmful or neutral in their effects.
However, the evolutionist believes in mutations as the source of all the diversity of life on earth today. This would require the production of untold numbers of beneficial mutations. That the same handful of examples is always offered is again testimony to the faith of the true believer. One of the favorite examples of beneficial mutations is the ability of bacteria to change so that they are resistant to antibiotics. Of course, that is beneficial only to the bacteria, not to the humans they infect.