Harmony and Conflict in the Living World - Alexander F. Skutch [7]
In the animal kingdom, the course of evolution has paralleled that of plants. Life is simple for the amoeba and other blobs of protoplasm that live always immersed in the water that forms the greater part of their substance; but as we all know, life is complicated for humans in our multiform, constantly changing environment. The more we contemplate the transformation, the more incredible it appears that organisms forsook the ease and security (except from other organisms) of their primitive aquatic ambience to live unquietly amid all the stresses and perils of the less stable aerial environment. Had they been forced by some external power to assume forms whose preservation demands ever-increasing effort, their metamorphosis would have been surprising enough. We marvel the more when we remember that the impulse that drove them from change to change has always come from within them.
It is not that the universe, or that immediately effective part of it that we call the environment, is actively hostile to life, as Bertrand Russell (1917) believed. Save for an occasional hurricane, volcanic eruption, or flood, the environment is passive enough. In many
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regions, it is so favorable for vital processes that it almost seems to invite the presence of living things. Its fitness to support them has many aspects. Water is, of all known liquids, that which best serves as a medium for intricate processes that can go forward only within a narrow range of temperatures; and it is the only liquid abundantly present on the surface of our planet. Among the properties that make it a fit medium for life are its high specific heat, which retards changes in temperature; its abrupt change from contraction to expansion as, in cooling, it approaches the freezing point, which causes it to congeal from the surface downward rather than from the bottom upward and increases the thermal stability at low temperatures of deep lakes and seas, making their complete congelation improbable. Add to this its chemical stability combined with its versatility as a solvent, and its capacity to form, with carbon, compounds rich in latent energy. Likewise oxygen, hydrogen, nitrogen, the sunlight, and the soil all have properties that make them peculiarly favorable for vital processes. The environment is friendly enough to life.
Life, on the other hand, often seems to challenge or defy the environment, like an aggressor invading a hostile land. Had it been content to remain in the warm seas where it began, in the humid tropical lands where today it flourishes most lushly, it might have existed in vast profusion yet remained in friendly inorganic surroundings. But not satisfied with these immense yet almost uniformly congenial domains, restless life, impelled by its own great capacity for multiplication, invaded the arid deserts, advanced far toward Earth's frigid poles, climbed ever higher up rocky mountain slopes, battling against thin air and intense insolation and cruelly sudden changes in temperature. On every front, life armed itself to battle with the environment, which is not intentionally cold or arid or changeableseized it by the throat, so to speak, and by sheer force compelled it to yield what imperious life needed and demanded. When conflict arises between life and its milieu, life is usually the aggressor; the passive environment is what it must be.
In these uncongenial regions where intrusive life exists precariously, a slight intensification of the prevailing conditions, such as more prolonged drought in an arid land or exceptionally intense
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It was once the habit to look upon all those features of Earth that make it a favorable home for living things as special provisions for this end. This interpretation