Wrong. That is not always the case.<quoted text>
Absence of evidence is not evidence of absence.
Unless you believe that DNA didn't exist before we had evidence of it.....
If someone claimed that someone was killed by sitting on top of 5,000 pounds of dynamite yet that body did not have a mark on it that would be evidence the person was not killed by 5,000 pounds of dynamite.
If either the Garden of Eden or Noah's Ark myth was true we would find a population bottleneck in all of life dating back to that event.
If the Noah's Ark myth was true we would find all sorts of deposits from a massive flood. There are no such deposits from the same time around the world.
Instead we find many different deposits from much smaller floods, if we find flood deposits at all of all different ages. Many of them older than the date of your mythical flood.