Functional morphology involves the study of relationships between the structure of an organism and the function of the various parts of an organism. The old adage "form follows function" is a guiding principle of functional morphology. The function of an organ, appendage, tissue, or other body part dictates its form. Furthermore, the function can often be deduced from the form. The idea of relating form and function originated with the French naturalist Georges Cuvier (1769-1832).
The primary task of functional morphology is observing living organisms to see how they live and function. From observations of living organisms, scientists also attempt to discern principles that will allow them to determine function from the forms of fossils, such as bones, shells, or whatever happens to be preserved from organisms that no longer exist. Theoretical morphology tries to determine the limits of form; not every conceivable form could actually exist in nature.
Functional morphology studies the ways in which structures such as muscles, tendons, and bones can be used to produce a wide variety of different behaviors, including moving, feeding, fighting, and reproducing. Functional morphology integrates concepts from physiology, evolution, development, anatomy, and the physical sciences, and synthesizes the diverse ways that biological and physical factors interact in the lives of organisms. Functional morphology and biomechanics allow scientists to observe and quantify not only how animal skeletons and joints move and how muscles work but also how these things relate to the diversity of animal behaviors.
Functional morphology helps to understand the form of modern animals. For example, even casual observation reveals that elephants have very thick legs relative to their body size when compared with smaller animals such as antelope or horses. This is not just a fluke of nature's design; elephants need thick legs to hold up their body mass. But why are the legs of an elephant proportionately thicker than the legs of smaller animals?
The mass of an object is related to its volume. Imagine an animal, an elk for example, scaled up to be twice as tall (about the height of an elephant) while keeping all proportions the same. An animal twice as tall as another animal of a similar shape will have much more than twice the volume. Because it is also twice as long and twice as wide, the scaled-up elk will have eight times as much volume as the normal-sized elk. Assuming bone and muscle density remain about the same, the scaled-up elk will also have eight times as much mass. However, the legs of the larger elk will only have four times the area of the legs of the normal-sized elk.
According to the principles of engineering, the strength of a column of bone and muscle is proportional to its cross-sectional area. Legs with only four times the cross-sectional area will not be strong enough to hold up eight times the weight. To hold up the scaled-up elk, its legs must be proportionately thicker than the legs of the normal-sized elk. Consequently, in order to attain the great size they have, elephants had to evolve legs proportionately much thicker than those of smaller animals.
Elephants also have large ears. Functional morphology helps to understand this feature as well. As elephants evolved to larger body size, the area of their skin did not increase as rapidly as their volume. Thus, the elephant's skin could not dissipate enough heat to keep the elephant cool. The elephant's relatively large ears, however, significantly increase its ability to give off heat. Forest elephants live in somewhat cooler environments, so their ears are not as large as elephants that spend more time in the sun.
Functional morphology also helps to understand the limits on the size of cells. If a spherical bacterial cell grows to twice its original size, it has eight times the volume but only four times the surface area. Because the cell absorbs nourishment through its surface, it must sustain eight times as much mass with only four times as much nourishment. At some point, a cell will become so large that it cannot absorb enough materials to sustain its mass, and it will then divide.
see also Allometry.
Curtis, Helena, and N. Sue Barnes. Biology, 5th ed. New York: Worth Publishing, 1989.
Cuvier, Georges. Memoirs on Fossil Elephants and on Reconstruction of the GeneraPalaeotherium and Anoplotherium. New York: Arno Press, 1980.
Gould, Stephen J. The Panda's Thumb. New York: Norton, 1980.
Huxley, Julian S. Problems of Relative Growth. New York: Dial Press, 1932.
Purves, William K., and Gordon H. Orians. Life: The Science of Biology. Sunderland, MA: Sinauer Associates Inc., 1987.
Thompson, D'Arcy W. On Growth and Form. Cambridge: Cambridge University Press, 1942.
Functional Morphology>FUNCTIONAL MORPHOLOGY
A couple walk hand in hand along the beach. Suddenly an ant appears at the top of a sand dune, scaring the wits out of the couple. This is no ordinary ant, this is a giant ant the size of an elephant! Since ants are extremely strong for such small animals, this gigantic ant must be unbelievably strong, able to throw automobiles around like toys, right? Actually, no. As an object increases in size, its weight grows much faster than its strength. When an object doubles in size, it becomes four times as strong, but eight times as heavy. The thin legs of the ant are strong enough to support several times its own weight. However, if the ant were scaled up to be as tall as an elephant, its legs would be too flimsy to hold up its own weight.