... It claims genetic science shows all humans descend from one woman (99k–200k years ago) ...
There is a simple reason for this and it is not because originally there was only one woman. Mitochondrial DNA is passed directly from mother to child, and that DNA determines the line of female ancestors. So,
Imagine a population of 100,000 women. In every generation, a woman can have:
- 0 daughters (her specific mitochondrial line ends).
- 1 daughter (her line continues).
- 2+ daughters (her line expands).
There is a high probability that any single line will eventually hit zero because of the women who have no daughters. Over thousands of generations, lineages go extinct one by one until, by process of elimination, only one line remains that hasn't been broken.
... It claims genetic science shows all humans descend from ... one man (120k–338k years ago)
This also has a reason that is similar but not as simple, but it is not because there was originally one man. Genealogical DNA is recombined at every generation and it is a fact that you have the same ancestors as every other person on the planet because your number of potential ancestors has expanded exponentially to far beyond the actual number of people that have ever existed. However, the number of markers is limited to a rather low number, so just like the fact that number of female lines eventually goes to 1, so does the number of male lines. That is my understanding.
Anyway, you can't claim that DNA proves the existence of Adam and Eve and also claim that the earth is 6000 years old, because the DNA also shows that the humans have been around at least a hundred thousand years.