Bacteria, like all organisms, mutate for a variety of reasons, but most often due to changes in their environment - like exposure to anti-biotics for instance.
One, and I'm only giving one example here, of a human evolutionary trait is tails.
Human beings retain the genetic code for vestigial tails. We have additional genes that "turn off" the coding so that most people do not actually have tails. However, the coccyx, or tailbone, is the remnant of a "lost" tail.
All mammals have a tail at one point in their development. In humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryonic development. This tail is most visible in human embryos 31-35 days old. The tailbone, (at the end of the spine), was no longer needed to assist with balance and mobility. It still serves some secondary functions, such as being an attachment point for muscles, which explains why it has not degraded further. (Natural selection - evolution)
Since tails are part of our genetic code, and part of our embryonic development, why would God have made that little detail if He actually fashioned us out of "dirt".
Doesn't it make more sense that He guided the process of evolution, and when we were "ready" gave us our immortal souls "in His image?"