Evolution tells us that there are things besides natural selection going on - there are mutations and genetic drift. If we boiled up some primordial soup today, a few billion years from now the planet would be a lot different due to that randomness.
A few years ago, a game called Spore came out. It was supposed to be a love ode to evolution because you got to introduce some historical contingency and then nature just got drunk and did her thing the rest of the time. The problem with the game isn't that you could never come up with a human, it's instead that almost everyone's creatures looked like this:
In the recent experiment, evolution was more like Spore than the fits and stops and starts. Obviously it was yeast, so eyes did not evolve and fade away multiple times but after 640 lines and all those generations, they ended up at really similar evolutionary endpoints.
On Genetic Literacy Project, I detail what was going on and why there seems to be diminishing returns - at least for beneficial mutations. If you get a negative one, you're probably still screwed.
Why random walks in evolution lead to the same place–and why biotechnology opponents should take note - Genetic Literacy Project
Citation: Kryazhimskiy S, Rice DP, Jerison ER, Desai MM, 'Microbial evolution. Global epistasis makes adaptation predictable despite sequence-level stochasticity', Science. 2014 Jun 27;344(6191):1519-22. doi: 10.1126/science.1250939
H/T Evolution’s Random Paths Lead to One Place by Emily Singer, Quanta