In “The Invaders” (Twilight Zone ;Episode 51), Agnes Moorhead, alone in her rural shack, is tormented by a tiny spaceship no larger than a salad plate. Or so it seems until the episode’s dénouement , when it is revealed that the spaceship is not tiny (it contains several average-sized humans). Instead, Moorhead is a giantess.
Such changes of scale have been a staple of imaginative literature from the mythical lumberjack Paul Bunyan, who was said to be so large that his footprints created Minnesota’s 10,000 lakes, to the miniature people created by Dr. Pretorius in Bride of Frankenstein (James Whale, 1935). There seems to be an enduring human fascination with people who look and act pretty much like us, and live in a world very much like our own, except for the fact that everything in that world including the people themselves are orders of magnitude larger or smaller than we are.
Such changes of scale without corresponding changes of form must remain the province of legend and literature, however: they are impossible in the real world. To understand why, you need only consult John Tyler Bonner’s eminently readable Why Size Matters. In this slim volume, he argues that size is the supreme regulating force in biology as well as the prime mover of evolution. Bonner sums up his arguments in five rules (given on page 5):
- Strength varies with size.
- Surfaces that permit diffusion of oxygen, of food, and of heat in and out of the body, vary with size.
- The division of labor (complexity) varies with size.
- The rate of various living processes varies with size, such as metabolism, generation time, longevity, and the speed of locomotion.
- The abundance of organisms in nature varies with their size.
The most famous literary example of physically impossible changes in size is Jonathan Swift’s Gulliver’s Travels. Among the creatures Lemuel Gulliver encounters in his travels are the Lilliputians, who are 12 times smaller than himself, and the Brobdingnagians, who are 12 times larger. If Gulliver were a man 5’8” in height, Bonner calculates that the Lilliputians would be just under 6” and weight less than a pound, while the Brobdingnagians would be 68’ tall and weight 12-13 tons.
Unlike the depictions by Swift (and numerous illustrators), in which members of both races appeared very similar (except for the change in scale) like Gulliver himself, Bonner argues that the Lilliputians would very likely have had stilt legs like a sandpiper and rapid, high-pitched voices, while the Brobdingnagians would have had massively thickened legs (resembling a person with elephantitis) and deep, slow voices. These changes in form would be necessary because not all dimensions of an object increase in direct proportion: for instance, weight rises as the cube of linear dimension, while bone strength increases as the square of linear dimension. Therefore, the bone structure of larger creatures must be proportionately more massive in order to support their weight.
Bonner convincingly demonstrates his thesis with many examples from evolutionary biology to the organization of contemporary human societies. For instance, the principle that complexity increases in proportion to size is upheld both by the diversity of cell types in large as compared to small creatures and by the greater specialization of labor found in human societies of differing sizes.
No mathematical sophistication is required to follow Bonner’s arguments: Why Size Matters supports its points primarily with line drawings and graphs illustrating the many characteristics of biological organisms, from shape and appearance to generation time and abundance, which vary in relation to size. In addition, Bonner writes in an informal, engaging style and with admirable clarity, so Why Size Matters can be enjoyed by everyone from a bright junior high school student to a professional scientists on her/her day off.
John Tyler Bonner is Professor Emeritus of Ecology and Evolutionary Biology at Princeton University. His research pioneered the study of cellular slime molds to understand evolution and development. Bonner has written or edited numerous books, including Lives of A Biologist: Adventures in a Century of Extraordinary Science (Harvard University Press, 2002) and First Signals: The Evolution of Multicellular Development (Princeton University Press, 2000).
Sarah Boslaugh (firstname.lastname@example.org) is a Performance Review Analyst for BJC HealthCare and an Adjunct Instructor in the Washington University School of Medicine, both in St. Louis, MO. Her books include An Intermediate Guide to SPSS Programming: Using Syntax for Data Management (Sage, 2004), Secondary Data Sources for Public Health: A Practical Guide (Cambridge, 2007), and Statistics in a Nutshell (O'Reilly, forthcoming), and she is Editor-in-Chief of The Encyclopedia of Epidemiology (Sage, forthcoming).