The splitting of one species into two distinct species, incapable of reproducing fertile offspring with each other, is a process that takes millions of years and is referred to by the technical name of Cladogenesis.
While this happens, it is possible that two species with a recent common origin can still breed with each other, but in general they produce hybrids that are sterile and die prematurely.
Examples in animals include the crosses between:
- horse and donkey (mule),
- lion and tiger (liger),
- zebra and donkey (zebroid).
This does not happen in plants. Hybrid plants are fertile in general.
Examples of typical hybrid plants are:
- bread wheat, the one we eat every day, which was the result of the hybridization of three wild kinds of wheat 10,000 years ago,
- grapefruit, a hybrid between pomelo and orange,
- mint, a hybrid between spearmint and water mint,
- and the bananas we all eat frequently.