Evolution is often characterised – particulary by those who argue against it – as a random process which could not possibly give rise to the complexity and diversity of life on Earth. How true is this?
Well, that characterisation is not at all accurate, and reflects a misunderstanding of how evolution operates.
Mutations – which produce new genetic material – are random. But the action of natural selection is anything but (see also a previous posting).
Natural selection works on the genetic variation generated by mutations and reshuffled in sexually-reproducing organisms by meiosis and fertilisation. Those individuals with genotypes that make them more likely to survive and reproduce tend to pass those genes on; less advantageous genotypes are culled. This process is not in any way random, but results in a population that is better-adapted to the prevailing environment.
Important point: evolution isn't progressive either. It doesn't work towards some predetermined goal. Species are 'improved' only in the sense of becoming better adapted to their current environment; evolution cannot prepare them for some future change in that environment.