Quite a lot of the single wild-caught baby Gorillas that found their way into Zoos in the early days, were given a young Chimpanzee as a companion to combat depression/loneliness. And even a few decades ago hand-raised baby Gorillas born in zoos were frequently raised with young Orangutans and Chimps if these were available in lieu of other young Gorillas. It was regarded, probably rightly, as being better than no Ape companionship at all. Zoos that did this include Twycross, Bristol, La Palmyre to name just a few. Nowadays there is a move away from handrearing/ lack of proper socialisation with other Gorillas from as early as possible, in nearly all cases. Of course this isn't the same as mixed exhibits using Gorillas and other species.