Occurrence of endemic species in South America and Australia is due to continental drift. Continental drift is the gradual movement of the continents across the earth's surface.
Darwinism claims that the fossilized remains of South American species are similar to those found in Africa and Australia.
Thousands of animals and plants were gathered and described by Darwin during the Beagle's trip (1831–1836). He studied how species in South America adapted to a range of environments, including rainforest, grassland, and mountain ecosystems. The species in the temperate areas resembled the species of South America's tropical regions more than they did the similar species of Europe's temperate regions. For instance, although there are no rabbits in Argentina's grasslands, there are rodents that resemble them. These rodents are not linked to European rabbits, but rather to other rodents found in South America.
Mutations happen in our cells all the time. It's actually how all humans grow and change. The vast majority of mutations are harmless. Thus, they aren't avoidable.