"Evolution begins when there is an error during reproduction and the new cell is different from its parent. Mutant cells usually die, and those that survive are likely to be disadvantaged by their mutation. Only very rarely will a mutant perform better than its parent. The descendents of the mutant cell may then successfully compete against the rest of the population and eventually replace them.

The more often an organism mutates, the faster it evolves, and so the faster it can adapt to changing conditions and the more successfully it can compete against other variations. The pressure to evolve faster has forced cell reproduction to maintain a consistently high rate of mutation. Only the need for enough healthy individuals to survive stops the mutation rate from being higher.

A larger population has a higher chance of producing a beneficial mutation. But then a considerable amount of time may need to pass before the mutant population grows large enough to have any chance of producing a second beneficial mutation.

This problem was overcome by the appearance of sexual reproduction. By combining the DNA from two parents, a child cell can inherit the beneficial mutations from two separate ancestries. Beneficial mutations can then spread back into an existing population, and this greatly magnifies the rate of evolution."