Chris Meissner, age 15, of Brodenton, Florida, for his question:
Why does a cow have four stomachs?
A cow lives with chronic indigestion, or so it seems. Every meal is followed by a long series of hiccoughs and cud chewing. This tiresome way of life is governed by the complicated stomach she inherited from her remote ancestors. They needed it to protect them from their mortal enemies and without it they would not have survived. In which case, the domesticated cow would not be with us. Her ice cream and other dairy products would be missing from our menu.
In nature, the reason for any biological feature is related to many other things, directly or indirectly. The cow's complicated stomach made it possible for her ancestors to survive and perhaps also made possible the age of mammals. Her earliest ancestors chewed and digested their food more or less like most other mammals. But their simpler stomachs caused far more serious problems than indigestion. Like most mammals of their day they were vegetarians. They had to spend long hours grazing and browsing. Digesting vegetation is a slow process and dining occupied most of the day.
They shared their long ago world with several cat, dog and bear type carnivores. These meat eaters had the role of reducing the vegetarian populations who otherwise would have multiplied too fast, devoured all the greenery and starved themselves out of existence. The most successful carnivores of each generation were the fastest, strongest and most cunning ones. Hence, they thrived and grew more menacing. The herds of primitive cattle, grazing out in the open, were at their mercy. Without some new device, the meat eaters would have devoured all the vegetarians thereby putting themselves and all the other mammals out of business.
However, the hoofed cattle developed a compartmentalized stomach that saved the day. This began when they discovered the swallow now chew later method of dining. While the carnivores dozed, usually at dawn and dusk, the vegetarians zippy toed into the open and filled their stomachs with hastily swallowed greenery. Then they retired to hide themselves in the shelter of the shady woods, coughed up gobs of food, patiently chewed the cud and reswallowed it to be properly digested. This cud chewing system was a life saver and gradually through the ages the cow stomach evolved separate compartments to cope with it.
The domesticated cow inherited her fancy stomach from her wild ancestors. When in the course of nature a simple organ evolves into a more complex one, there is no way to return to the original model. For centuries, the dairy cow has led a pampered life, protected from the prowlers and pouncers that plagued her ancestors. She no longer needs her complicated digestive system, but there is no way to change it.
When a cow grazes, each mouthful is swallowed whole and goes down to fill the rumen compartment. Later, she hiccoughs to bring up a gob of moist food and patiently chews it. This is reswallowed and goes down to be partially digested in the reticulum compartment. Digestion is completed as the food goes on through the omasum, the psalterium and finally the abomasum compartments.