Tell me how 6 billion humans can descend out of two, and yet, cousins marrying today produces birth defects in their offspring at a very high frequency.
Also, what about a cyclical universe? _____ >< .....-----*****-----....._____ >< .....-----***** etc.
And it’s not a stumbling block for Theists
Oh, yes it is! You're just attempting to explain it with a God cure-all.
A cyclic universe is nonsensical if the universe has always existed — because the laws of thermodynamics would ensure that the amount of energy in an infinitely existing universe would be 0.
This is simplistic stuff...
The two original humans, created before the fall, were physically perfect and their genes contained all the information necessary to produce all the variation we see today. After the Fall, the corruption allowed mutations and gene drift that cause the problems today.
A cyclical universe would require that the rate of observed expansion be slowing instead of accelerating, which is what astronomers are currently seeing.