"Did" is a past tense verb. Therefore, saying "did you know" asks if you have previously known something. "Do" is the present tense, so saying "do you know" would ask if you currently know. As a native speaker, I would be more likely to ask using did because normally our intention is that we want to find out if the person already knew this or if it is new information for them. Both would be correct though, depending on the context. The phrase "do you know" is usually used when you are trying to find out information that you do not know. For example, you might say "Do you know where Patty's office is?" Hope this helps. Let me know if you have more questions. Good luck! :)

'Did you know...?' = We use this when we are about to tell someone an interesting piece of information. 'Do you know...?' = We use this when we want the someone to give us some information which we need. So which of these do you think is more appropriate for your sentence about the apes?