"After considering the possibilities, I don't think that we can prove what happened either way."
Sure we can, without any doubt,
Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned: Rom 5:12
If sin entered into the world (and the word for world is cosmos, that means there is sin throughout the universe) through Adam only,
then,
the other people God created would not die and still be alive today,
they wouldn't become sick because they wouldn't be under the curse of Adam,
their women wouldn't suffer with pain during childbirth,
So ask yourself, seen any of them running around lately, or do you know anyone that knows anyone that knows anyone that has met these people?
More important and much more serious, ...if this were true then these people would be sinless, they would be gods, and the next step in that parade is we can become like God ...we would have a bunch of little christs running around on the planet, ...now where have I heard that before, oh yeah, I remember, on TV.
Paul tells us there are winds of false doctrine Eph 4:14 blowing across the planet and we are to be careful to not be deceived by believing them,
To the Law and to the testimony! If they do not speak according to this Word, it is because no light is in them. Isa 8:20
Be careful and be blessed,
Gene