Final answer:
Evolution is driven by migration, selection, and adaptation, causing isolated animal groups to evolve distinct characteristics and fill new ecological niches in different environments, especially following catastrophic events.
Step-by-step explanation:
The process of evolution can be influenced by factors such as migration, selection, and adaptation. For instance, after a flood, various groups of animals may find themselves in different environments, leading to each group experiencing unique selective pressures. Migration can lead to geographical isolation, as seen in the hypothetical example of mice separated by a river, eventually evolving into distinct species. Selection plays a role when traits that enhance survival in the new environment are favored.
For example, the arctic fox and ptarmigan both evolve white coverings in winter for camouflage, despite not sharing a common ancestor. Adaptation to new environments can lead to different species filling the ecological niches that become available. A catastrophe, like a massive flood, can provide the conditions for a sudden evolutionary burst as new species emerge to fill the vacated ecological roles.