Sexual Method Of Reproduction Governed By The Surface Of The Earth
( Originally Published 1940 )
In concluding, we shall endeavour to review the whole history of the evolution of the species, but specially now in its dependence on the history of the evolution of the surface of our earth, which after all governs everything that happens to us. It will then be seen that the gradual and complete conversion of the vegetative into the sexual method of reproduction, is ultimately an adaptation to the catastrophes of the earth's surface, which have always governed those influences which we have recognised as decisive.
In the beginning, when the surface of the globe was covered everywhere with a layer of water, there was nothing but water-organisms which only increased their numbers vegetatively, without sexual stimuli or sexual life.
Then later on, when the earth's surface became uneven, with local heaps of organic debris, the mosses which require moisture above everything, developed; at that stage vegetative reproduction was still the principal thing, while sexual reproduction remained the exception.
Still later, as here and there large tracts of dry land appeared, still covered, but now with marshes and bogs, the vascular cryptogams evolved, and sexual reproduction began to take a step forward with these. On dry hills and mountains, however, the coniferae grew, which high in the sun and air almost exclusively relied on sexual reproduction.
The majority of our monocotyledons also still prefer a marshy soil, and increase as well by bulbs and rootstalks, as they do sexually by seeds. In the tropics, however, the maize, rice and palms increase in the heat of the sun, just as corn in well manured land does with us, almost exclusively in the sexual way.
Like the latter, most of the dicotyledonous species prefer a loose soil and plenty of sun; they then reproduce mostly, and many of them exclusively, through seeds. Especially in the mountainous regions they revel in an abundance of sunshine, through which the most beautiful and abundant flora develop and delight us.
In the animal world, the vegetative form of reproduction was forced to give way much earlier and more completely to the sexual form, because animals possessing the power of locomotion can seek the sunshine for themselves, and their bodies are in various ways exposed to all kinds of local stimuli; whereas the plants, so thoroughly vegetative, are always doomed to lie quietly half buried in the darkness and moisture of the earth. Yet since the earliest times there have existed many varieties of worms and such-like which spend all their lives in darkness and water or moisture; and in many of their species the vegetative method of reproduction still rules rather than the sexual.
Fish and amphibia live in the water, but spawn in the sunshine.
The warm-blooded animals come higher in the scale with their increased oxidation and their increased sexuality.
But still all the higher species of plants and animals in which the sexual life has triumphed, always begin by passing through an asexual period of life in non-irritating moisture and deep-darkness; their nuptial flight, however, takes place on a fine day in the height of summer or in a midsummer night's dream.