CHAPTER 7        

ENVOI

Size and the actual organisms that are measured are rather like shadow and substance. The organisms are material objects. In correlation with their size, they come in many shapes and have different physiologies, degrees of internal complexity, generation times, life spans, speeds, and frequencies to their songs. A beast’s size is like a shadow: it has no substance. It is simply a statement of how much matter makes up a particular living entity.

What is remarkable is that although size is no more than a shadow, no more than a description, a property, it nevertheless exerts enormous power over the living world; it drives the form and function of everything that lives. How can this be so?

The root reason is natural selection. The size of an organism is under constant selective surveillance. Nature is made up of a vast network of size niches, and all living forms are always faced with the possibility that it may be advantageous to have their descendants become larger or smaller. If they are animals, size may be important for avoiding predators, or catching prey; for plants it may be important for success in the competition to catch the rays of the sun for photosynthesis. In microorganisms the most obvious advantages in becoming larger may also involve greater speed to pursue prey or escape predators. Becoming larger by multicellularity may mean more effective dispersal of spores, or more effective digesting of food, where the presence of more digestive enzymes are insured by increasing numbers of cells. The list could go on, as I have argued in much of this book. The key point is that size changes—increases or decreases—will have advantages or disadvantages and will be encouraged or discouraged by natural selection. Selection is the motive force for size change.

And if the size is changed there will be a myriad of consequences, especially if it is increased. It will mean various constraints bear down: size is volume, yet life’s activities require the appropriate surface to go with the volume and the result will be different shapes for different sizes. This will have many ramifications affecting properties such as metabolism and locomotion. It is particularly interesting that as the volume increases, there is an increase in the division of labor in the form of the number of cell and tissue types. Unless these and many of the associated changes occurred, larger organisms simply could not manage. They would not exist. Size increase has forced all these changes. The shadow is not really just a shadow: it is much more. Even though it is not substance, it is a dictator that holds complete sway over what on organism will look like and how it will function. Size rules life.

In the cases of size decreases, size plays a somewhat different role—it is no longer the absolute dictator. This is because having less bulk may permit a decrease in the structures that are involved in matters of strength or surfaces for diffusion, but they do not necessarily require it. It could be that with continued size decrease, they may not have room for all the structures their larger ancestor possessed and may ultimately have to shed some of them; clearly size decrease is far less demanding than size increase.

If we stand back even farther, we see a principle here that goes beyond life. In the inanimate physical world, size has the same effect as it does on living organisms: Galileo made this clear right from the start. A small pendulum swings faster than a large one; a large boat such as an eight-oared shell will move faster than a one-man single. I pointed out earlier that it takes longer to build an aircraft carrier than a rowboat, but also that the larger ship has a vastly larger division of labor in its parts. The proportions of bridges or of buildings must differ with size increase because of the weight-strength relationship. The engineer who builds airplanes, engines, or bridges must make size one of his prime concerns; if it is neglected, all his endeavors will fail.

One could say that what makes life unique is natural selection that culls so that only the efficient constructions survive, while the equivalent for human constructions is whether or not they work. Mechanical or physical efficiency in engineering structures simply has a different method of selection, just as the selection forces of economic efficiency governed the division of labor in human societies. Size is ubiquitous and casts its shadow on all material things, both the living and the nonliving.

Putting all these matters concerning size together leads to another insight. The size rules that have been laid out show that there is a connection between strength, surface activities, division of labor, and all activities that involve rates of processes such as metabolism, generation times, longevity, speed of locomotion, and even the abundance of organisms in nature. What connects them all is size. A change in weight will either require, or be correlated with, a change in strength, in surfaces, in the division of labor, in all the time-related rate processes, and even in the density of the distribution of organisms in nature. Each of the five size-related categories is interdependent with all the others: one changes and they all change. It is much the same thing as one finds in the gas law where changes in temperature will change the pressure or the volume of a gas: a similar kind of connectivity is found in the size rules.

All the thoughts in this book reflect the human preoccupation with size. This is so for Galileo and all the scientists who have followed him up to this very minute as I write these words. It is equally so in literature from Sinbad the Sailor through the delights of Gulliver’s Travels, right up to many artists and writers today. And one can add to them a multitude of aspects of human existence: architecture, engineering, business, transportation, and innumerable others. There is no corner of human endeavor and human thought that escapes the tentacles of size. Couple size with the evolution of living organisms—and this becomes the book I have written.