FullReads

The third definite objection made by Mr. Martineau is of kindred nature. The Hypothesis of Evolution is, he thinks, met by the insurmountable difficulty that plant life and animal life are absolutely distinct. “You cannot,” he says, “take a single step toward the deduction of sensation and thought: neither at the upper limit do the highest plants (the exogens) transcend themselves and overbalance into animal existence; nor at the lower, grope as you may among the sea-weeds and sponges, can you persuade the sporules of the one to develop into the other.”

This is an extremely unfortunate objection to raise. For, though there are no transitions from vegetal to animal life at the places Mr. Martineau names, where, indeed, no biologist would look for them; yet the connexion between the two great kingdoms of living things is so complete that separation is now regarded as impossible. For a long time naturalists endeavored to frame definitions such as would, the one include all plants and exclude all animals, and the other include all animals and exclude all plants. But they have been so repeatedly foiled in the attempt that they have given it up. There is no chemical distinction which holds; there is no structural distinction which holds; there is no functional distinction which holds; there is no distinction as to mode of existence which holds. Large groups of the simpler animals contain chlorophyll, and decompose carbonic acid under the influence of light, as plants do. Large groups of the simpler plants, as you may observe in the diatoms from any stagnant pool, are no less actively locomotive than the minute creatures classed as animals seen along with them. Nay, among these lowest types of living things, it is common for the life to be now predominantly animal and presently to become predominantly vegetal. The very name zoospores, given to germs of algae, which for a while swim about actively by means of cilia, and presently settling down grow into plant-forms, is given because of this conspicuous community of nature. So complete is this community of nature that for some time past many naturalists have wished to establish for these lowest types a sub-kingdom, intermediate between the animal and the vegetal: the reason against this course being, however, that the difficulty crops up afresh at any assumed places where this intermediate sub-kingdom may be supposed to join the other two.

Thus the assumption on which Mr. Martineau proceeds is diametrically opposed to the conviction of naturalists in general.

* * * * *

Though I do not perceive that it is specifically stated, there appears to be tacitly implied a fourth difficulty of allied kind–the difficulty that there is no possibility of transition from life of the simplest kind to mind. Mr. Martineau says, indeed, that there can be “with only vital resources, as in the vegetable world, no beginning of mind:” apparently leaving it to be inferred that in the animal world the resources are such as to make the “beginning of mind” comprehensible. If, however, instead of leaving it a latent inference, he had distinctly asserted a chasm between mind and bodily life, for which there is certainly quite as much reason as for asserting a chasm between animal life and vegetal life, the difficulties in his way would have been no less insuperable.

For those lowest forms of irritability in the animal kingdom which, I suppose, Mr. Martineau refers to as the “beginning of mind,” are not distinguishable from the irritability which plants display: they in no greater degree imply consciousness. If the sudden folding of a sensitive-plant’s leaf when touched, or the spreading out of the stamens in a wild-cistus when gently brushed, is to be considered a vital action of a purely physical kind; then so too must be considered the equally slow contraction of a polype’s tentacles. And yet, from this simple motion of an animal of low type, we may pass by insensible stages through ever-complicating forms of actions, with their accompanying signs of feeling and intelligence, until we reach the highest.