Natural selection
It is not possible that through natural selection a "perfect" individual is formed, since the base from which natural selection acts is as a response to a specific environment, so very efficient adaptations for a given environment may not be, or even be harmful, in another one.
On the other hand, natural selection acts on the genetic basis of the individual, that is, on potential characters that are encoded in its genetic material and were not being expressed. For this reason, natural selection does not form "perfect" traits but rather shows the best traits available in the individual's gene pool for a specific environment at a given time.