It by no means necessarily follows, however, that this tendency is actually being carried into effect, and that new species of the higher animals and plants are actually now produced.

They may be so or they may not, according as existing circumstances favour, or conflict with, the action of those laws.
It is possible that lowly organized creatures may be continually evolved at the present day, the requisite conditions being more or less easily supplied.

There is, however, no similar evidence at present as to higher forms; while, as we have seen in Chapter VII., there are _a priori_ considerations which militate against their being similarly evolved.

{226} The presence of wild varieties and the difficulty which often exists in the determination of species are sometimes adduced as arguments that high forms are now in process of evolution.

These facts, however, do not necessarily prove more than that some species possess a greater variability than others, and (what is indeed unquestionable) that species have often been unduly multiplied by geologists and botanists.