Board Thread:General Discussion/@comment-28925112-20160730202210/@comment-4991168-20160830104301

The problem with this theory is that it assumes the current set of characters has been around since the time of Chara and Asriel, while we only know that for sure about Toriel, Asgore, and Gerson.

It is more likely that a human or two fell before some of the current monsters were born or while they were children. Toriel also seems to believe Asgore personally finished some of them off.