Gorillas don’t stand upright and they don’t walk on two legs, but always with their legs and arms combined. That is just the way nature made them.
With everything else,there is evolution – species didn’t stay the same for too long time. We are talking about long time in evolution,which can be 1000s,100s of 1000s or millions of years.
This beautiful gorilla has spent so much time with humans / not that he had the chance for anything else/ that he decided to try to imitate them and start to walk like them. He taught himself how to do it!
Here is another video of a gorilla walking. Planet of the Apes can’t be too far now: