In order for Adam and Eve to replenish the earth, they would have needed to have lots of children and they in turn would have to marry each other, brother and sister. Wouldn’t the children have had lots of defects, similar to what happens today if one were to marry a sibling? Or perhaps the Lord realized this and prevented it from happening.
Genetic defects in offspring that are not evident in the parents come from the matching of recessive genes for the same defect. If the parents had no defective genes they could not be passed on to the children. I would suggest that there have been no more perfect physical specimens on the earth, save Jesus Christ only, than the first two inhabitants of the earth, our primal parents, Adam and Eve. I imagine that defective genes began to be incorporated into the chromosomes of their descendants through mutations that seem to occur from time to time.