Answer:
It may mean that the two proteins evolve in slightly different directions, so that one version works better in one set of conditions and the other under different conditions.
Please note that the cost to the organism of making two proteins instead of one is minimal. Basically, it involves adding one coding gene to the tens of thousands of genes that are already there (assuming that the sum of the amounts of the two proteins is about the same as the amount of the original one protein).
Different versions of the same protein may also be made by differential splicing of the mRNA, or by the many mechanisms of post-translational modification.
Explanation:
im lazy so imma leave this out
