Can an animal evolve after birth?
No.  Certainly not.  There is only a very limited number of cells in the body of any creature which pass on genetic material to the offspring generation; these are referred to as gametes.  Mutations to these cells, however, do not affect the parent in the least, as their sole function is to produce offspring.

One gamete from the father &amp; one gamete from the mother fuse to produce a child with a combination of genetic code, which means that mutations in those gametes (which did not affect the parent) will be present in every cell of the child's body, and affect the child.

Furthermore, do remember that most mutations are not "enhancements"; rather the vast majority of mutations are harmful.

After birth (and really, long before birth) mutations acquired in the organism are unable to be passed on to the offspring, unless they happen in the gametes, in which case they do not affect the parent carrying those mutations.