Evolution and the Emergence of Complex Organisms

How did all the trillions of different organisms on Earth come about? And why are so many of these organisms more complex than their bacterial ancestors? The theory by which scientists try to answer these questions is the theory of evolution. In essence, the theory uses only a few basic processes. Organisms produce (many) offspring. These inherit variable characteristics. As a result, they differ in their performance in a given environment. The differences in performance lead to non-random elimination. The result is a select group of survivors. Survivors start producing offspring again. And then the story repeats itself. The result is a pedigree, a pattern that results from underlying processes. From this simple basis, many questions about evolution can be addressed.