After so many millions of generations, why hasn't all life deteriorated and gone extinct?
I don’t know that is a question that YEC ask and that old earthers haven’t answered in a satisfactory way.
there are many papers (for example
Why we are not dead one hundred times over - PubMed) that deal with this problem and no author claims to have a definitive answer.
Obviously thihs doesn’t mean that therefore the earth is young, but it means that there is a problem that has to be solved. Which is fine scientists are looking for a solution to this problem only fanatic evolutionists from YouTube and forums pretend that evolution (Darwinism) is a perfect theory that has no holes nor unsolved problems
Your question indicates you don't understand how natural selection works.
note how you are avoiding the question
There probably was no single 'first'. Exclusively sexual reproduction likely developed gradually, and inbreeding might very well have been problematic
.
Necesarirly there had to be a “first” organism capable of reproducing sexually and supposedly (according to the theory of evolution) we all descend from that organism.
If the mechanisms of evolution didn't work, where'd the diversity come from, and why are we still here? What's your alternative explanation?
I don’t know and nobody knows,,,,, all the mechanism that have been proposed in the literature have both advantages and problems……….. scientist are still working on this problem.
My personal guess…….. diversity comes mainly from “non random mutations”