The Factors of Organic Evolution

The Factors of Organic Evolution is by Herbert Spencer, reprinted with additions from The Nineteenth Century. The preface says the two parts of the essay were originally published in The Nineteenth Century for April and May 1886 respectively. The preface says that, though the direct bearings of the arguments in the essay are biological, the argument in its first half has indirect bearings upon Psychology, Ethics, and Sociology.

The essay says some few, rejecting also the hypothesis indicated by both Dr. Darwin and Lamarck, accepted the single vera causa, the modification of structures resulting from modification of functions. A pump is described: when the plunger of the pump is raised and relieves from atmospheric pressure the water below it, the atmospheric pressure on the water in the well, not being balanced by that on the water in the tube, forces the water higher up the tube. The essay says the differentiating action of the medium never ceased to be a co-operator in the development of the first animals and plants.