Sorry but I'll never buy the single ancestor argument. Just doesn't seem logical. But I do appreciate your efforts in attempting to educate me.
You commit the classical logical fallacy of argument from personal astonishment. "Seeming logical" is not a valid test of the truth of an idea. The evidence that supports or falsifies truth is what counts. I do wonder if common descent would seem logical to you if it didn't conflict with your religious beliefs? Somehow I suspect that if the Bible described something like evolution in Genesis then suddenly common descent would "seem very logical" to you.
Here is a question. You are in a room with 25 other people, what is the chance that 2 people in that room share the same birthday. If you haven't studied probability theory you will probably be very surprised to discover that the probability is around 60%. Now, does that "seem logical"? Because it is true.
Other illogical but true ideas: Light waves are bent by gravity. No mathematical system can ever prove all true mathematical propositions. The universe contains at least 1,000,000,000,000,000,000,000 suns like ours. Time slows down at high velocities. On the moon a feather falls at the same speed as a ton-weight. No two integers a and b exist such that a/b is exactly equal to Pi. All of these ideas seem intuitively illogical to most people, but they are all true.