Page:The Zoologist, 4th series, vol 5 (1901).djvu/58

36 student of the dominant phase of thought which now distinctly influences all philosophy, and less evidently moulds ethics and theology as well. Darwinism is no longer the sole property of the naturalist; it has invaded the "social contract," and the doctrine of "natural selection" as loosely used in social economy is often little different from utilitarianism, or what has been well called the cult of laisser faire. The last remarks are opportune, because Mr. Headley devotes the second part of his book to "Problems of Human Evolution," and in these pages we can now only refer to his first instalment dealing with the factors of organic evolution.

Mr. Headley surveys these factors under the usual different classifications, viz. Heredity, Variation and Death, the Lamarckian Principle, Natural and Sexual Selection, and Isolation, and describes and estimates their powers from the standpoint of his own analysis. The result is a most readable and instructive representation of much evolutionary evidence with advocacy of "selectionist" principles. (The term "selectionist" must now be recognised; it is largely used, and seems to have an extra Darwinian definition.) If there were no struggle for existence, many animals would, in a short time, become dominant by number. We have had many examples given us, and now Mr. Headley, who is an ornithologist, adduces the case of the House-Martin (Chelidon urbica):—"It is quite common for them to have three broods in the year, and we are not beyond the mark in allowing them four in each brood. In order to avoid any possible exaggeration, we will assume that each pair has eight young ones each season. At this rate, if there were no deaths, there would in five years be six thousand two hundred and forty-eight House-Martins sprung from one pair."

We are glad to find our author is free from the crass Cartesianism so prevalent among many "Neo-Darwinians" of the present day. "The problem of the origin of consciousness puts us on the horns of a dilemma. Either consciousness is present in the lowest forms of life, or else it was introduced at a higher stage of development. The latter alternative is abhorrent to the very principle of evolution. We are driven, then, to believe that even the micro-organisms, whether animal or vegetable, have some consciousness, however dim."