The most recent archaeological evidence (published last week in Nature, 08/09/2007, p. 688) suggests more trouble on the horizon for Biblical "literalists", the pinheads who think that it's not enough for the Bible to be "true", it has to be "literally, word for word, jot and tittle true", otherwise it's all just a pack of lies. According to these folks, God created the entire material and spiritual universe in six twenty-four hour periods, and then rested for twenty four hours (maybe he wanted to watch himself on 24 Hours). Since this all happened nearly 6000 years ago it's a rather difficult hypothesis to test, but since it sez so in the Bible who needs to test it? It's proven science, folks. Anyway, on this view of things, all of humanity is descended from an original pair of humans, Adam and Eve, who had no navels since they themselves were directly created by God, not born from other animals.
The latest archaeological evidence suggests that Homo habilis and Homo erectus were living broadly sympatrically in the same lake basin for nearly half a million years. If this is so, then it is at least possible that present day homines sapientes are descended from more than one genetic lineage. There is genetic evidence supporting the hypothesis that we are all descended from a single lineage, but this most recent evidence may complicate that somewhat. The possibility of more than one lineage has always existed, of course, but it is interesting to contemplate the further possibilities opened up by this work.