Ancestors of the giant panda had rounded paws with five short toes. The giant panda of today has a sixth toe, a thumb-like appendage that helps with grasping bamboo. The presence of the thumb is most likelythe result of

convergent evolution

Explanation:

Convergent evolution is a feature of organism to develop similar traits as other animals in order to adapt to their habitat. Similarly to bats and birds both developing "wings".

The thumb-like appendage in a panda is actually a false thumb. Since Giant pandas require a large amount of bamboo to maintain life. They must be very efficient in tearing and stripping the leaves for fast feeding. Pandas that developed this trait were better able to survive and pass this along to their offspring.