Mitochondrial Eve is the most recent common ancestor of all humans via the mitochondrial DNA pathway. In other words, she is the MRCA found when ancestry of all living humans is traced back in time, following only the maternal lineage. The mitochondrial DNA pathway is equivalent to maternal lineage, because mitochondrial DNA is only passed down from mother to child, never father to child.To find the Mitochondrial Eve of all living humans, one can start by tracing a line from every individual to his/her mother, then continue those lines from each of those mothers to their mothers and so on, effectively tracing a family tree backward in time based purely on mitochondrial lineages. Going back through time these mitochondrial lineages will converge when two or more women have the same mother. The further back in time one goes, the fewer mitochondrial ancestors of living humans there will be. Eventually only one is left, and this one is the most recent common matrilineal ancestor of all humans alive today, i.e. Mitochondrial Eve.
It is possible to draw the same matrilineal tree forward in time by starting with all human female contemporaries of Mitochondrial Eve. Some of these women may have died childless. Others left only male children. For the rest who became mothers with at least one daughter, one can trace a line forward in time connecting them to their daughter(s). As the forward lineages progress in time, more and more lineage lines become extinct, as the last female in a line dies childless or leaves no female children. Eventually, only one single lineage remains, which includes all mothers, and in the next generation, all people, and hence all people alive today.
