Professor Walter J. Veith said:
Carnivores: Carnivores kill and eat other animals and in the case of carnivorous mammals, they are classified as such on the strength of their teeth. A carnivore is equipped with the necessary weapons to kill and catch other animals, but this equipment need not necessarily have been designed for that purpose. Yes, possessing the equipment pre-adapts an organism to become a carnivore but this need not have been its original disposition. Panda bears, for example, are classified as carnivores on the strength of their teeth, but they eat bamboo. The same type of teeth can kill and tear flesh, but as in the case of the Panda bear, that need not be what they were designed for. The same can be said for the whole family Ursidae, the bears, that subsist largely on a vegetarian diet eating mainly berries. It is true that they will eat fish if available and can be opportunist carnivores, but they are equally at home on the fields grazing alongside buffalo.
Carnivores are not only adapted for meat eating in terms of their teeth, but their intestines are also shorter than those of herbivores. It is very interesting that diet has an amazing effect on intestinal structure. Intestines have a tremendous capacity for growth, and if sections are removed during operations, some parts can regenerate and grow back to their original length. Carnivores have short intestines because meat does not contain fiber and a short intestine is thus advantageous so that the food does not remain trapped in the intestines for long periods of time. Also, the food of carnivores is high-energy food that is absorbed rapidly. Carnivores whose diets are changed to herbivorous diets adapt rapidly to these diets and subsist very well on them. Lions will also preferably eat the contents of the rumen of a kill first. The rumen contains fermented plant products, and there are numerous accounts of lions and other carnivores that were raised on plant diets such as grains and would not touch meat even if presented to them. Dogs and cats can also subsist very well on vegetarian diets and in fact live much longer and are less aggressive on such diets. The teeth of these animals that act as shears could equally well have been used to shred tough plants in the past, and the fact that they dont do so now could simply be as a result of the destruction of their original food source. There is plenty of evidence in the palaeontological record that far greater varieties of plants existed in the past than exist today.
Destruction of habitat changes the diets of animals even in our day. Chipmunks traditionally eat seeds in the forests, but with acid rain leaving its mark, food sources are often becoming inadequate, and it is not unusual to see these cute herbivorous animals tearing away at road kills to augment their diets with meat. This is a case of a herbivore becoming a meat scavenger as a result of changing circumstances. . . .