It may take longer to figure out fully where the species has evolved from. To show gorilla evolution, it is appropriate to look at primate evolution. About fifteen million years ago, apes and many other of its forms evolved. They lost the ability to move through the branches. Asian apes diverged from the African apes 12.5 million years ago, which then gave rise to the orangutans and gibbons.
Primate ancestry is very difficult to research, since it involves the evolution of man.
Most likely, they were small and rodent-like. We are not sure what the early relative of the gorilla was, but it can be traced back to an early ape known as Proconsul africanus. The chart on the last page details the development of primates. Minor differences between the lowland and mountain forms suggest that the divergence between the two occurred in the past. There seems to be two primary factors that limit the growth of gorillas as a species.