We begin by noting a few facts about life’s general behaviour, starting with plants. Outwardly, plant life might appear to be passive and uneventful; endless cycles of germination, development, replication and death, with random mutations—possibly of significance to future species—happening in between. A cursory look at the life of animals might suggest the same pattern. However, as we will soon be reminded, the full story is much more complex. Each one of life’s many species is competitive, assertive, territorial, and occasionally very aggressive. Each does its utmost to expand into neighbouring territory, wherever it exists and whenever the opportunity arises.
Plants fit this description, once we look at what happens over several generations. Most gardeners know that any plant will expand its domain unless curbed. Creeping Charlie is a good example; it will sow seeds and extend runners ad nauseam, and is very difficult to eradicate. Mushroom fairy rings graphically and accurately portray this expansionist behaviour, as underground mycelia spread, then fruit. In fact, the history of any plant species may be viewed as one long quest to gain territory, and an outside intercession of some kind or another is always needed to halt the process. Plants invariably enlarge their domain until prevented by an inhospitable climate or by soil that lacks nutrients or is toxic in some way, or until they are overcome by some disease agent or eaten by insects or animals.
Insects exhibit exactly the same behaviour. We have all likely read about calculations showing that the offspring from one pair of flies, unless checked in some way, would number enough to blanket the world after a few weeks. Only impediments such as lack of food, its own excrement, poisons of some kind, parasites, attacks from aggressors seeking to control the same environment—some kind of external force—will stop the population from exploding. Locusts dramatically demonstrate this phenomenon. Every few years, huge swarms of these grasshoppers arise and decimate vast areas. Insects, like plants, multiply, strengthen their control of local food sources, increase again in number, move outward, and repeat the sequence if not halted by an opposing force. In fact, it has been said that if a catastrophe killed most of the life on Earth, insects would survive and evolve to dominate what remained.
Animals, too, behave in this manner, as demonstrated by many animal population-cycle studies. Plant food supplies increase, so the number of rabbits increases; the fox population then builds, and a bunny take-over is prevented. The number of rabbits then decreases, so the fox population declines, and before we know it, we have rabbits galore again. (It is a seven-year cycle, roughly, in this example; eight years for the lemming/stoat cycle.)
No species self-limits its own population. Microbes and mice, birds and bees, fish and flowers, horses and humans; all multiply profusely unless prevented. An external agent is always required to stop the expansion. Not infrequently, this external factor is itself living; it stops the growth of another by using this other as a source of food. The net effect of this has been to produce a precarious balance, maintained as our biosphere. The balance is preserved by each species defending what it possesses, and attacking to take what it needs.
Now, let’s consider what all this might imply. If every form of life behaves this assertively, then the assertive trait must have been present very early in the evolutionary chain. And, indeed, it was, because exploiting surrounding territory turns out to be the main characteristic that distinguishes living material from non-living material. To understand this more completely, we must again start at the beginning of the story.
- Darwin used the words “competition” and “competes” frequently in On the Origin of Species. He knew that life is assertive. Tennyson, too, knew what much of life was about, writing, “nature, red in tooth and claw,” when penning In Memoriam.
- Thomas Malthus, in An Essay on the Principle of Population, published in 1798, was among the first to write that life (although he limited his discussion to human life) would continue to grow in numbers unless prevented by external forces. Darwin’s thoughts were influenced by that essay. This chapter takes for granted that Malthus’ principles continue to operate, and apply to all forms of life.
- Even we “modern” parents do not automatically limit the number of children we have. We use contraceptives only when we consider that additional progeny will curtail, endanger, or affect the quality of our life, or adversely affect the lives of others we care about, or when a restriction is imposed and enforced, such as in China where more than one child per couple is made illegal and penalized.