>5 dependent (on or upon something uncertain); conditional

going on from the same source:

As it happens, our ape ancestors branched off and survived, while our later hominid ancestors died out. If those hominids had survived, then our species, in its many colors, would coexist with truly less developed hominids. It'd be a different ball game. But that's not how it worked out. We are one -- and only one --people.