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Our wonderful life-supporting planet is home to a remarkably diverse and complex spectrum of living organisms. And although all living things do share some common traits and similar biochemical pathways and cellular functions, there are many notable differences that make each creature stand out from the crowd. So even with the thread of sameness joining all the planet's life forms, diversity and difference makes us take note of each creature’s uniqueness. Maybe that’s why the cat is America’s favorite housepet ... cats are different!
This extraordinary four-legged feline has, for all of recorded time, evoked wonder and surprise, superstition and affection, damnation, and deification. From pharaohs to philosophers to paupers, the companionship of and affection for cats has been a result of the cat’s unique ability to make us humans gaze in awe and admiration.
Eons of special environmental circumstances have forced the cat to evolve some interesting and individualized biochemical activities. Let’s take a peek at how unique the cat is inside, in that mysterious universe of liver and kidneys and glands and fluids where a million chemical reactions are going about their biological business in silent obscurity. And to make our little peek at the inner workings of the cat more interesting, let’s contrast a few of the cat’s biological activities to those of our next most favorite companion the dog.
In so many obvious ways, cats look, act, react, and respond differently than dogs. You never see a cat happily wag its tail; a dog’s reflexes are quick, a cat’s reflexes are incredible; dogs are doers, cats are watchers. These differences are easily noted by simple observation. Now let’s explore some of the unseen microscopic world of the cat -- the invisible world of metabolism and chemistry that is just as real as those traits we can see with our eyes.
To begin with we must get a good grip on two terms ... carnivore and omnivore. The cat is considered by scientists to be a strict carnivore and the dog is considered to be an omnivore. Both species are in the Class Mammalia and the Order Carnivora, but here’s the difference: The cat cannot sustain its life unless it consumes meat in some form. Dogs, however, are able to survive on plant material alone; they do not have to consume meat. But always keep in mind that dogs do best and by nature are primarily meat-eaters. Just because by definition they are omnivores (can digest and utilize plant and animal food sources) does not mean that plant material alone makes a good source of nutrition for the dog. Far too many dogs have been undernourished by those cheap grain-based dog foods. And grain-based cat foods are even worse!
So a good way to think of it is that cats are carnivores, dogs are omnivores, but they both have evolved as hunters of other animals in keeping with their nature as meat-eaters.
There are numerous chemical substances that are required for a cat to remain alive. These substances, some very complex chemical molecules and some very basic and simple, must be provided along the internal chemical reaction pathways at all times. Like other living plants and animals, the cat can manufacture most of its own required substances within its own body’s chemical factory. For example, Vitamin C is a requirement for life sustaining processes for us Mammalia, and dogs and cats make plenty of their own within their body’s chemical factory -- the liver. We humans don’t make enough within our body chemical factory ... so to keep ourselves alive we have to find some Vitamin C already made (preformed) somewhere in our environment, gather or capture it, then eat it. Without the Vitamin C, we’d die.
Dogs and cats don’t have to worry about gathering, capturing, and eating other preformed Vitamin C. They don’t care where their next grapefruit will come from because they make all the Vitamin C they need inside their own personal chemical factory.
On the other hand, there are numerous nutrients and chemicals that cats need that they can only acquire if they eat animal-derived tissues. That is, they need to prey on other living creatures that do make the essential chemicals that cats don’t! Out of necessity, the cat has evolved ways to hunt down, capture and eat this prey in order to "borrow" the prey's nutrients.