THIS section must begin with a warning or two. One of the most surprising characteristics of man, considered as an animal species, is his capacity for moralising. The words ‘society ‘and ‘social ‘have an immediate association in the minds of most of us with the words ‘good,’ ‘bad ‘and ‘responsibility.’ It must be made clear, therefore, that when we set out to investigate the social relation of species to species, we are concerned simply with elucidation and our use of words derived from human affairs must not be taken to imply the usually associated moral judgments. This may sound easy enough, but a simple test will indicate probable difficulties : use the word’ parasite ‘of any organism or consider the female spider’s habit of devouring her mate and see if you do not feel some moral indignation.
Nevertheless, so long as we remember the danger of pushing comparisons too far, we may, with profit, apply some of the words and ideas derived from a social organism which we know pretty well, namely, our own species, to those which we know less well—the millions of species of plants. Such a method is almost certain to lead into some errors but no other course is really practicable. Even if it were, we may take it as next to impossible for any ordinary person to divest himself of all the preconceptions set up in the whole course of his conscious life. We must, therefore, begin with some fairly simple facts which everybody is likely to know, and use them to get notions which will broaden the scope of our inquiry.
SEPARATING THE INSEPARABLE: A FEAT OF THE HUMAN MIND A REMARKABLE human ability is that of considering separately things which are never so in our experience. This is a useful trick—indeed for some scientific purposes a necessary one—but we must be careful how we make use of it. When an engineer discusses the attributes of a weightless beam it is not because he has any idea of using such a dangerous structure, supposing he could lay hands on one. It means little more than an intention to consider his problem apart
from weight. Similarly, when an experimental biologist keeps his plants at a temperature constant within one-hundredth of a degree centigrade, he does not imagine he is reproducing natural conditions. He wants to be able to say no more than : ‘Whatever else causes the changes in my plant, it is not variation in temperature.’’
So in this consideration of social relations : we may think of the behaviour of a particular species as if no others were concerned, but we must never quite forget that it is a mental feat to do so. Any gardener will tell us that an absolutely pure growth of a single species of plant is a practical impossibility. He knows that he is engaged in a continual fight against the intruders which he calls weeds. Even the elaborate pure-culture methods of the bacteriologist cannot exclude unwanted organisms all of the time.
In the broad sense it is true to say that no portion of space which is capable of supporting living organisms remains unoccupied for long. So much is this true that places which seem fantastically improbable from our own standpoint support a living population of some kind : the thin water-film on the surface of a strong acid like sulphuric; the intestines of animals; the arctic ice; the sandy deserts of Arabia; all these places, and many others quite as strange, provide conditions in which some living things can carry on their life-processes.
It is not very surprising, therefore, that naturalists have not yet given up hope of finding new species of plants and animals, but, on the contrary, are painfully aware that they are ignorant of the mere existence of enormous numbers of inhabitants of this earth, let alone of anything about their methods of getting a living. It is obvious that of those parts of the world which man has subdued to his purposes we know more concerning the composition and behaviour of the other organisms inhabiting them than we know of the places where he is still a total stranger or very occasional visitor. As land animals we certainly know more of the land than we know of the depths of the sea or the heights of the atmosphere and stratosphere.