Evolution works through mutation and selection.  Mutations might occur during replication if the enzyme DNA polymerase makes a mistake.  But it rarely makes a mistake.  Mutations also occur because of radioactivity or ultraviolet light from the Sun or cosmic rays or chemicals in the environment, all of which can change the nucleotides or tie the nucleic acids up in knots.  If the mutation rate is too high, we lose the inheritance of four billion years of painstaking evolution.  If it is too low, new varieties will not be available to adapt to some future change in the environment.  The evolution of life requires a more or less precise balance between mutation and selection.  When that balance is achieved, remarkable adaptions occur.

Carl Sagan (Cosmos, p. 26)

If an omniscient god guided evolution, the enzyme DNA polymerase wouldn’t make mistakes — even though such mistakes are rare.  Moreover, the balance between mutation and selection wouldn’t be more or less precise; it would be exact.  What Carl Sagan has described is what one would expect of a process that isn’t guided by an omniscient being.