studies of African tribal culture has shown that each individual tribe developed its own unique form of combat, but nothing that can be called a 'system' in our terms. What we commonly think of as a martial art are not taught within the tribe as a 'martial art'.. they are individual warfare techniques and dance movements. The idea of a 'martial art' is not part of most tribal cultures... its just a combination of skills they learn. Many of the games played by children in these cultures develope and harness combat skills, but the games are not thought of as training techniques.
To have a representative from one of the surviving traditional tribal families sit down and discuss thier 'martial arts' is almost impossible, since that concept is alien to them. They can discuss various hunting techniques, particular dance rituals, and common close cambat or wrestling concepts... but this is not considered something that can be classified as a 'martial art' in thier minds. While many of them may 'wrestle' with each other on occasion, they do not practice it.. its just something they do from time to time. There may be similarities seen in habits and tendancies displayed while wrestling, but it is not something that is developed intentionally or uniformly. They have no specific schools that teach combat skills, and there are no formal instructors that teach these skills.
It might be possible to spend enough time with a particular tribe to gather enough information to catalog what WE could define as thier 'martial art'. Unfortunatley, anthropologists find it difficult to distinguish between a combat skill that is used in daily routine, and a daily routine that could be interpeted as having combat applications. For example, when watching a ritual dance, WE might see a series of combat activities, because we are LOOKING for them.
Among the South American tribes, we can find things that can more closely be considered a martial art.
I hope i made sense here. These are merely the conclusions reached during my own efforts to research the subject while i majored in cultural anthropolgy, and they seem to reflect the observations of the larger anthropological community.