_The Science of Organic Evolution, or Bionomics._ As a science, evolution is the study of changing beings acted upon by unchanging laws. It is a matter of common observation that organisms change from day to day, and that day by day some alteration in their environment is produced. It is a matter of scientific investigation that these changes are greater than they appear. They affect not only the individual animal or plant, but they affect all groups of living things, classes or races or species. No character is permanent, no trait of life without change. And as the living organism or group of organisms is undergoing alteration, so does change take place in the objects of the physical world about them. "Nothing endures," says Huxley, "save the flow of energy and the rational order that pervades it." The structures and objects change their forms and relations, and to forms and relations once abandoned they never return. But the methods of change are, so far as we can see, immutable. The laws of life, the laws of death, and the laws of matter never change. If the invisible forces which rule all visible things are themselves subject to modification and evolution, we have not detected it. Its cosmic movements are so fine as to defy human observation and computation. In the control of the universe we find no trace of "variableness nor shadow of turning." "It is the law of heaven and earth, whose way is solid, substantial, vast, and unchanging." But the things we know do not endure. Only the shortness of human life allows us to speak of species or even of individuals as permanent entities. The mountain chain is no more nearly eternal than the drift of sand. It endures beyond the period of human observation. It antedates and outlasts human history. So does the species of animal or plant outlast and antedate the lifetime of one man. Its changes are slight even in the lifetime of the race. Thus the species, through the persistence of its type among its changing individuals, comes to be regarded as something which is beyond modification, unchanging so long as it exists. "I believe," said the rose to the lily in the parable--"I believe that our gardener is immortal. I have watched him from day to day since I bloomed, and I see no change in him. The tulip who died yesterday told me the same thing."