A common belief among Christians is that physical death entered the world as a result of the Fall. This view is expressed on the Got Questions site: “Because of the Fall, death became a reality, and all creation was subject to it. All men die, all animals die, all plant life dies.”
But the view that death, namely physical death, entered the world because of the Fall is incoherent. Using a description of life at that time and in that place (i.e., the Garden of Eden), as related in the Bible, one can logically conclude that it is ecologically impossible that such could have been the case.
At the time of the Garden of Eden, only plants were available for food to all organisms, by God’s design, as stated in Genesis 1:29-30.
“Then God said, ‘Behold, I have given you every plant yielding seed that is on the surface of all the earth, and every tree which has fruit yielding seed; it shall be food for you; and to every beast of the earth and to every bird of the sky and to every thing that moves on the earth which has life, I have given every green plant for food,’ and it was so.” (Genesis 1:29-30)
Organisms found at the time in the Garden of Eden included every plant yielding seed on the face of the earth, every tree that has fruit yielding seeds, every beast of the field, every bird of the sky, and cattle.
“Out of the ground the LORD God caused to grow every tree that is pleasing to the sight and good for food; the tree of life also in the midst of the garden, and the tree of the knowledge of good and evil.” (Genesis 2:9)
“Out of the ground the LORD God formed every beast of the field and every bird of the sky, and brought them to the man to see what he would call them; and whatever the man called a living creature, that was its name.” (Genesis 2:19)
“The man gave names to all the cattle, and to the birds of the sky, and to every beast of the field, but for Adam there was not found a helper suitable for him.” (Genesis 2:20)
Ok, showing that physical death was present at that time is possible through placing these original descriptions into the context of elementary ecology. One of the keys is cattle. Cattle belong to the family Bovidae. All bovids are ruminants. Ruminants have a 4-parted stomach in which food is digested with the help of microorganisms that break down complex materials in plants, such as cellulose, and release fatty acids and amino acids essential to cattle. As the plant food moves through the complex stomach and the remainder of the digestive tract, these microorganisms move with it. Eventually, some of these microorganisms are eliminated in the feces of the cattle. Being mutualistic symbionts adapted to live in the gut of these cattle, they do not survive well outside of the host body. Thus, they die unless they are ingested by a ruminant.
Another cause of mortality is herbivory itself. Much grazing by cattle just trims tissue from food plants, and most plants recover from that. But some herbivory, even by cattle, uproots plants and thus kills them. When one adds to this source of death, sources from non-cattle herbivores like voles and gophers, which consume plant roots, then herbivory as a source of plant death can be appreciable.
In addition to these clear examples of death in the Garden of Eden, there are likely others based on competition. Plants are under intense competition both within a species and between species. This competition results from limited supplies of light, carbon dioxide, water, and required inorganic nutrients like nitrates, phosphates, and potassium. Much of this competition occurs through shading as taller plants shade out shorter one, or plants with deeper roots obtain more water and inorganic nutrients in the soil than do plants with shallower roots. Thus, there is almost certainly death of the plants that are less competitive at gaining these resources.
Finally, competition between and within herbivore species is another source of death. If population sizes of these beasts of the field were greater than what could be supported by plants, there would be death. The fact that all animals were herbivorous means there were no carnivores present to hold herbivore populations in check. This absence thus would allow herbivore populations to rise temporarily above the level that could be supported by plants, at which time some individuals would die from lack of sufficient nutrients.
Thus, just because all animals ate plants in the Garden of Eden, it does not follow that there was no physical death there.
However, this all says nothing against the idea–from a biblical perspective, anyway—that the kind of death entering the world at the Fall was spiritual death.