Darwinian evolution, the process by which species change over time. For example, dinosaurs evolved over millions of years, expanding from a common ancestor to a very wide variety of forms. Depending on who you ask, modern birds are, in fact, still descendants of a specific group of dinosaurs today.
Another example is the wide variety of dogs that exist today. They are all descended from wolves, based on interactions with humans in our early societal phases. After a while we started selectively breeding them for certain traits. Excellent herding skills like the Australian Shepard, their ability to guard and protect like the German Shepard, and even just to be cute like the Pomeranian.