The way I see it is that genetics should teach us a lot about our history.
I don't understand though, according to genetics, we are all derived from one Y male and one mitochondrial female. So how do we tell if a bottleneck has occurred if we all have the same genes? Do we contain somewhere in our genes all the alleles for every possible physical trait?
I'm not talking about agenetic bottleneck in just our species. I'm talking about one in all the species of the planet.
A global flood that kills off almost all of the animals would leave a record in the form of a bottleneck in the genetic information in all of the animals that now exist after the flood.
That we don't see that bottleneck shows that there wasn't a flood.