Background Essay: Animal Mouths
Environmental conditions have shaped the evolution of every organism on the planet. From the structure of a maple tree's cells, to the camouflage of a praying mantis, to the wariness of a gazelle, countless physical and behavioral traits have grown out of the interaction between organisms and their environment. These traits, called adaptations, are the result of natural selection, and they give an organism the ability to survive and reproduce in a given set of conditions.
One component of the environment that has been particularly influential in the evolutionary process is food. Over millions of years, the amount and type of food available to a species has dramatically influenced both the manner in which individuals of that species find food and the physical traits that help them catch and eat their food most efficiently.
The mouth structure of the anteater, for example, demonstrates the influence a rich food resource can have on the evolution of an organism. Ants and termites are certainly plentiful, but they're tiny and must be consumed in huge quantities if an animal is going to survive on them and nothing else. The giant anteater of South America and similar creatures, including Africa's pangolin and Australia's spiny anteater, all possess adaptations that allow them to do just that. Each of these creatures has a long snout and tongue, salivary glands that produce copious amounts of sticky saliva to coat the tongue, and powerful forelimbs with long claws for digging. Nearly every physical feature of these creatures is specialized for eating small insects that live in underground colonies.
The distant ancestors of anteaters and pangolins were not nearly so specialized, however. They had much shorter snouts, shorter tongues, and legs and feet that were no doubt better for running but not nearly as good for digging. But millions of years ago, when these unspecialized creatures roamed the earth, ants remained an untapped resource with tremendous potential. Similarly, the energy-rich juices inside plants were also untapped. If you go back far enough in time, insects like fruit-piercing moths and snout beetles didn't exist either.
Over time, the ancestors of all of the creatures pictured in this image -- in fact, the ancestors of all organisms -- changed in tiny increments. An ancestor of the anglerfish may have been born with a mouth ever so slightly larger than the average fish of its species. This may have had no advantage whatsoever. Or, the larger mouth might have made this individual more successful than other fish at catching prey, giving the animal a better chance of surviving and passing its large-mouth genes on to the next generation. In such a way, tiny beneficial changes can be passed from generation to generation and can, over time, become much bigger changes that dramatically influence a species' way of life.