The seven mitochondrial DNA lines simply shows that the human race descends from just seven females at its lowest ebb. That does not mean there were never more than seven, nor that the seven were all homo sapiens: there is a strong likelihood we have neanderthal DNA as well to various amounts. What esle disappeared in the past is anybody's guess, and what that did equally so. As animals like ligers and tigons show, there is a possibility of cross-species breeding, and without reference DNA there is no knowing what they found actually is: going further in this way is irrational, it confuses remote possibility with probability and thereby discredits the hypothesis and its proponents.