>>63
AFAIK, how gravity is generally understood has basically become law. Newton's law of universal gravitation, for example. Though, the law itself draws criticism from people who do mathematical calculations, and other such later problems with that were mooted with Einstein's general relativity, which at this point is not really just a theory anymore. Though to think that every single thing about gravity in our universe is understood is just folly.
I see where you're going with this, people are not going to deny the existence of gravity since evidence of it has been procured, studied, and examined. So there is truth that proves it exists.
However, we're talking about possible civilization in Sub-Saharan Africa independent of external support, and to my knowledge, the existence of such a civilization hasn't been proven false, so based just on that, to state that there never was such a civilization to be true, is committing a logical fallacy.
Argumentum ad ignorantiam (argument to ignorance) specifically, as I mentioned earlier in this thread in
>>38.