While natural selection is the driver for evolution, the development of characteristics isn't any more "random" than organic chemistry is. Most advanced organisms have a huge "backlog" of junk in their genes that still have the potential for generating a relatively complex new feature if they're expressed by some accident. You don't have to "randomly" assemble thousands of genes into a new form. Sometimes it's just evolution throwing a "switch" to turn old genes on. The further along the evolutionary tree an organism is, the more possible this becomes. This is probably why evolution seemed to proceed so slowly in the early eons of life on Earth, but seems to go at a pretty good clip now in higher animals and plants.

This is why it would be a lot easier to engineer teeth into a chicken than it would be to engineer teeth into a jellyfish. A chicken still has bits of leftover blueprints from everything its ancestors had before it was a chicken.