The design information for DAS was already present before the Fall, perhaps in latent or masked form.
This implies that the Fall was foreknown by God, which of course reflects His omniscience, and also is clearly stated in various Bible passages which speak of such things as God choosing us "in him before the foundation of the world" (Ephesians 1:4). This information was allowed to become expressed, either through direct unmasking at the Fall, or through the natural processes of recombination and selection. If the latter were the case, this would again involve the foreknowledge of God, this time that there would be only a short time between creation and the Fall. Otherwise, these DAS would have come to the fore in Eden eventually.
However, it is not easy to imagine genetically how such self-activation could take place for such a vast number of creatures which must also interact ecologically (the appearance of a defense structure must take place very smartly after one's enemy has a new weapon).