system
Given the following post, respond as if you're commenting on Reddit:
human
If we can all be traced back to the same common female ancestor, why don't we all have the same mitochondrial DNA?
gpt
Mitochondrial DNA also undergoes mutation: it's just very slow.

Normal sexual reproduction forces lots of mixing and matching of gene sequences, creating very distinct *patterns*, even though the number of actual *mutations* -- change to a piece of code from any of the pre-existing versions out there -- is relatively small in any given period of time. 

Mitochondrial DNA, down the maternal line, and Y-chromosome DNA, down the paternal line, do not undergo a process during reproduction that strongly induces any changes or rearrangements. But, just like any genetic code, they are subject to "accidental" mutations. Therefore, even though there may be just one "Eve", there have been occasions at which the mitochondrial DNA has "branched", even if only slightly, down the ages. Some of these branches have then subsequently sub-branched, and so on.

These instances of branching aren't wholesale overhauls by any means. It's more like how you can tell different editions of the same book apart because the publisher who put out the second edition put a comma on page 548 where a semicolon was before. Then, in subsequent runs, some publishers kept using the original first-edition file, but some based their editions off the second edition instead, which had the semicolon. And one of *those* printers at some point changed the word "axe" to "ax", so among future editions, there will be printers who base their runs off that edition, and it'll have a semicolon plus an extra "e", and so on.