"It was in the attempt to ascertain the interrelationships between species that experiments n genetics were first made. The words "evolution" and "origin of species" are now so intimately associated with the name of Darwin that we are apt to forger that the idea of common descent had been prominent in the mnds of naturalists before he wrote, and that, for more than half a century, zealous investigators had been devoting themselves to the experimental study of that possibility. Prominent among this group of experimenters may be mentioned Koelreauter, John Hunter, Herbert Knight, Gartner, Jordan. Naudin, Godron, Lecoq, Wichura--men whose names are familiar to every reader of Animals and Plants unders Domestication."

“If species had really arisen by the natural selection for impalpable differences, intermediate forms should abound, and the limits between species should be on the whole indefinite. As this conclusion follows necessarily from the premisses, the selectionists believe and declare that it represents the facts of nature. Difference between species being by axiom indefinite, the differences between varieties must be supposed to be still less definite. Consequently the conclusion that evolution must proceed by insensible transformation of masses of individuals has become an established dogma.”

“I am well aware that some very eminent systematists regard the whole problem as solved. They hold as Darwin did that specific diversity has no physiological foundation or causation apart from adaptation, and that species are impermanent groups, the delimitations of which are ultimately determined by environmental exigency or "fitness." The specific diversity of living things is thus regarded as being something quite different in nature from the specific diversity of inorganic substances. In practice those who share these opinions are, as might be anticipated, to be found among the 'lumpers' rather than among the 'splitters.' In their work, certainly, the Darwinian theory is actually followed as a guiding principle; unanalysed intergradations of all kinds are accepted as impugning the integrity of species; the underlying physiological problem is forgotten, and while the product is almost valueless as a contribution to biological research, I can scarcely suppose that it aids greatly in the advances of other branches of our science.”

“I well remember receiving from one of the most earnest of my seniors the friendly warning that it was waste of time to study variation, for "Darwin had swept the field." Parenthetically we may notice that though scientific opinion in general became rapidly converted to the doctrine of pure selection, there was one remarkable exception. Systematists for the most part kept aloof. Everyone was convinced that natural selection operating in a continuously varying population was a sufficient account of the origin of species except the one class of scientific workers whose labours familiarised them with the phenomenon of specific difference. From that time the systematists became, as they still in great measure remain, a class apart.”

“Misconception was especially brought in by describing descent in terms of "blood". The common speech uses expressions such as consanguinity, pure-blooded, half-blood, and the like, which call up a misleading picture to the mind. Blood is in some respects a fluid, and thus it is supposed that this fluid can be both quantitatively and qualitatively diluted with other bloods, just as treacle can be diluted with water.”

“In the light of the new knowledge various plausible, but frequently unsatisfying, suggestions put forward, especially by Wallace, Weismann, and their followers, as probable accounts of evolutionary progress, must be finally abandoned.”

“That the variations are controlled by physiological law, we have now experimental proof; but that this control is guided ever so little in response to the needs of adaptation there is not the smallest sign.”