The mountains and deserts of Namibia hide many treasures - diamonds, gold, uranium, strategic minerals. But on the afternoon of June 4, 1991, we were searching Namibia's mountains for a rarer kind of stone, fossilized evidence of human evolution in southern Africa. What we found instead was the rarest "diamond" of all, one that no one had ever seen before on the African continent south of equatorial East Africa. What we found was incontrovertible evidence that prehuman "apes" were living in southern Africa millions of years before Australopithecus roamed the veld. Keywords: Miocene, hominoids, Namibia, paleoanthropology, primate evolution.