I come from a version of unorthodox Islam where we believe that all though all the people of the world today are descended from Eve and Adam, Eve and Adam were not the first humans; they are simply the first of today's humans. Adam's creation from mud is taken to be a metaphor for evolution, for The Qur'an also makes it quite clear that GOD has a very specific way of creating modern humans - by formation within a womb followed by birth. Humans are born from female wombs. Therefore, Adam was born from his mother's womb.
Even if Adam and Eve were, however, the first humans entirely, it seems to me that Adam would have had a tribe. If Eve and Adam were the first of all people, and had no parents, still, they and their children would have constituted a tribe. For their children branched off and started their own families, and thus, there would have been a group of families that shared common progenitors. That, I believe, is the definition of a "tribe." "Clans" are technically supposed to be families that belong to specific tribes. So in at least one way or another, Adam and Eve would have had a tribe. And if they were not literally the first humans on Earth, then Adam would have come from his parents' tribes, and Eve would have also inherited a tribe. So they still would have a tribe; for either Eve would have been "married" into Adam's inherited tribe, or vice versa, and their children would therefore have inherited a tribe.
So...genetically speaking, if we all descend from Adam and Eve, we all are part of the tribe of Eve and Adam. If that's true, would that mean that to divide our race into separate tribes in modern times, is arbitrary and meaningless? We're ultimately all from the tribe of Eve and Adam, (theoretically).