Page:Popular Science Monthly Volume 64.djvu/507

Rh unknown millions of years it has had to do with forms innumerable, a great battle going on in which myriads of unlike combatants were pitted against one another, each species being produced in such multitudes as to give it the fullest opportunity to sustain itself if capable. At every stage of the conflict the best adapted forms crowded down or annihilated their inferior competitors; themselves to be similarly dealt with when some new and superior combatant appeared. One needs only to look down the long record of paleontology, and consider that this represents only unit survivors of untold myriads, to recognize that nature has dealt with a superabundance of material, and to conceive that the final result may have been inevitable rather than fortuitous.

If we attempt to review the course of organic evolution upon the earth, we find ourselves confronted with so many types of life, so great a diversity of forms, such varied methods of motion and degrees of activity, that it is quite out of the question to deal with the subject adequately in a brief space. We can simply glance at it here, as an attempt to follow the whole line of progress would lead us too far afield.

Taking organic evolution as a process of colloid cell development—in distinction to the inorganic crystal development—we meet with a probably very long period of pristine evolution in which a single cell composed the whole organism. From this period examples indicating perhaps nearly the whole process of evolution still survive. The possibilities of progress in this direction were apparently very fully tried before organisms composed of a number of cells appeared. But when these came they quickly showed their superiority to the single-celled type alike in size and in complexity of organization.

From the basic generalized condition of living substance two great organic kingdoms arose, the fixed and the moving forms, plants and animals, the one living upon inorganic, the other upon organic material. Between these two inevitable resultants of the nutrient conditions the question of comparative rank is self-evident, the animal takes precedence of the plant. But the development of the latter was only in a minor degree due to inorganic influences. In water, where the animal assault on plants is not great nor varied, their evolution has been small. On land, where it has been severe and diversified, plant evolution has been large. But in no instance has it advanced from the purely physical to the conscious stage.

It is to the metazoa that we must go for the higher stages of evolution. Of the varied phases of this type of life, we can refer only to those of general character. No matter upon what planet life may have originated, we can not well avoid the conclusion that it must have had the organic cell as its unit, and that everywhere in its upward progress the many-celled self-moving form, feeding upon organic nutriment.