The reader will now begin to understand the sense in which polarity applies to these complex conditions of an advanced evolution.
To return, however, from this digression to the point at which it began, viz. the origin of life, we have to show how the law of polarity prevails in the organic as well as in the inorganic world. In the first place the material to which all life is attached, from the speck of protoplasm to the brain of man, is strictly a chemical product of atoms and molecules bound together by the same polar laws as those of inorganic matter.
In like manner all the essential processes by which life lives, moves, and has its being, are equally mechanical and chemical. If the brain, receiving a telegram from without through the optic nerve, sends a reply along another nerve which liberates energy stored up in a muscle and produces motion, the messages are received and transmitted like those sent by a voltaic battery along the wires of a telegraph, and the energy is stored up by the slow combustion of food in oxygen, just as that of the steam-engine is produced by the combustion of coal. All this is mechanical, inorganic, and therefore polar.
But when we come to the conditions of life proper, we find the influence of polarity mainly in this: that as it develops from simpler into more complex forms, it does so under the law of developing contrasts or opposite polarities, which are necessary complements of each other’s existence. Thus, as we ascend in the scale of life, we find two primitive polarities developed: that of plant and animal, and that of male and female.
CHAPTER VII.
PRIMITIVE POLARITIES—PLANT AND ANIMAL.
Contrast in developed life—Plants producers, animals consumers—Differences disappear in simple forms—Zoophytes—Protista—Nummulites—Corals—Fungi—Lichens—Insectivorous plants—Geological succession—Primary period, Algæ and Ferns—Secondary period, Gymnosperms—Tertiary and recent, Angiosperms—Monocotyledons and Dicotyledons—Parallel evolution of animal life—Primary, protista, mollusca, and fish—Secondary, reptiles—Tertiary and recent, mammals.
Animals or plants? Judging by first impressions, nothing can be more distinct. No one, whether scientific or unscientific, could mistake an oak tree for an ox. To the unscientific observer the tree differs in having no power of free movement, and apparently no sensation or consciousness; in fact, hardly any of the attributes of life. The scientific observer sees still more fundamental differences, in the fact that the plant feeds on inorganic ingredients, out of which it manufactures living matter, or protoplasm; while the animal can only provide itself with protoplasm from that already manufactured by the plant. The ox, who lives on grass, could not live on what the grass thrives on, viz. carbon, oxygen, hydrogen, and nitrogen. The contrast is so striking that the vegetable world has been called the producer, and the animal world the consumer, of nature.
Again, the plant derives the material framework of its structure from the air, by breathing in through its leaves the carbonic dioxide present in the atmosphere, decomposing it, fixing the carbon in its roots, stem, and branches, and exhaling the oxygen. The animal exactly reverses the process, inhaling the oxygen of the air, combining it with the carbon of its food, and exhaling carbonic dioxide. Thus, a complete polarity is established, as we see in the aquarium, where plant and animal life balance each other, and the opposites live and thrive, where the existence of either would be impossible without the other.