Can you share any insight as to why the fall of man, our sin, had to affect the animals as well?
God put everything under Adam’s dominion and stewardship. Genesis 3 tells us God cursed the whole earth as a result of Adam’s sin. That Curse had an ongoing dramatic effect on both humankind and animals, as part of creation. Human beings and the earth are inseparably linked; there is a metaphysical and moral link between mankind and the physical universe.
The Bible teaches that the whole universe experienced the Curse as a result of humanity’s sin, and consequently the whole creation (not just the earth) groans, awaiting its redemption, which will come at our resurrection (Romans 8:19-23). I believe when Scripture says that death came through Adam, it means that God’s creatures didn’t die before people sinned—animal suffering came because of humanity’s fall. (Note Paul’s argument in Romans 8.)
As the entire Creation, including animals and plants and all nature, fell on humanity’s coattails, so the entire Creation shall rise on our coattails as beneficiaries of Christ’s redemptive work and resurrection. As goes humanity, so goes all Creation: the earth, the animals, everything. As Creation wasn’t only about us, so redemption is not only about us.