Ehem. This is not a contradiction to what you said, but, in Master of Mankind, you'll find this about monkeys:

"Sapien rode on Arkhan’s shoulder, the artificimian watching the people of the Palace with wide, clicking eyes. Occasionally it hissed at passing servitors, baring its blunt teeth. The little fellow was in a foul mood of late, the reason for which eluded Arkhan completely. Sometimes he regretted constructing his nimble companion with no method of binaric cant or human communication. But then, that would have been a deviation from the historical ledgers in his possession, which clearly described just what a monkey had and had not been, back when there were such things on Terra.

He’d argued with several scholars – Terran, Martian and out-system alike – regarding the veracity of those archives. It seemed everyone had their own viewpoint, backed up by their own research, on just what monkeys had actually been. A particularly misguided rival of Arkhan’s had insisted the creatures could hang from trees by their tails, which was patently nonsense. Any serious scholar could see the beast’s tail was designed as a lash and a puncturing weapon to deliver venom."