Page:Popular Science Monthly Volume 12.djvu/195

Rh It is to be regretted that this phrase "natural selection" has been introduced. It is very unscientific, very inferior to the old expression adaptation. It implies a personification of Nature. It is anthropomorphic. But Nature never selects, never accepts or rejects, knows nothing about duties, nothing about fitness or unfitness. Nature simply obeys laws.

Natural selection is thus supposed to perpetuate an organism after adaptation to its environment has taken place. The change implied by adaptation must precede it. It should be regarded rather as a metaphorical expression than a scientific statement of an actual physical event.

Darwinism, therefore, does not touch the great question as to the manner in which variation of organisms arises. It only teaches how such variations are perpetuated.

The publication of Humboldt's "Essay on the Geography of Plants" (1805) first formally drew the attention of botanists to the connection between the distribution of plants and the distribution of heat on the surface of the earth. As an advance is made from the equator toward the pole in either hemisphere, the mean annual temperature declines, and in succession a series of vegetable zones is encountered, merging gradually into each other, though each, where best marked, is perfectly distinguished from its successor. In the tropics there are the palms which give so striking a characteristic to the landscape, the broad-leaved bananas, and great climbing plants throwing themselves from stem to stem like the rigging of a ship. Next follows a zone of evergreen woods, in which the orange and citron come to perfection. Beyond this, another of deciduous trees, the oak, the chestnut, and the fruit-trees of our orchards. Here the great climbers of the tropics are replaced by the hop and the ivy. Still farther is a belt of conifers, firs, larches, pines, and other needle-leaved trees; and these lead through a range of birches, becoming more and more stunted, to a region of mosses and saxifrages, but which at length has no tree nor shrub; and finally, as the perpetual polar ices are reached, the red-snow alga is the last trace of vegetable organization.

A similar series of facts had long previously been observed by Tournefort in an ascent of Mount Ararat. The distribution of vegetation from the base to the top of the mountain bears a general resemblance to the distribution from the base to the polar regions. These facts were generalized by subsequent observers. It was established that there exists an analogy between horizontal distribution on the surface of the globe, and vertical distribution at different altitudes above the level of the sea. Even in the tropics, if a mountain be sufficiently high, a short ascent suffices to carry us from the characteristic endogenous growths at its foot through a zone of evergreens