There is more beauty and unity of design in this continual balancing of life to circumstance, and greater conformity to those dispositions of nature … - Patrick Matthew

Throughout this volume, we have felt considerable inconvenience, from the dogmatical classification of plants, and have all along been floundering between species and variety, which certainly under culture soften into each other.

Matthew's response: To me the conception of this law of Nature came intuitively as a self-evident fact, almost without an effort of concentrated thought. Mr Darwin here seems to have more merit in the discovery than I have had; to me it did not appear a discovery. He seems to have worked it out by inductive reason, slowly and with due caution to have made his way synthetically from fact to fact onwards; while with me it was by a general glance at the scheme of Nature that I estimated this select production of species as an a priori recognisable fact – an axiom requiring only to be pointed out to be admitted by unprejudiced minds of sufficient grasp.

The circumstance-adaptive law, operating upon the slight but continued natural disposition to sport in the progeny (seedling variety), does not preclude the supposed influence which volition or sensation may have over the configuration of the body. To examine into the disposition to sport in the progeny, even when there is only one parent, as in many vegetables, and to investigate how much variation is modified by the mind or nervous sensation of the parents, or of the living thing itself during its progress to maturity; how far it depends upon external circumstance, and how far on the will, irritability and muscular exertion, is open to examination and experiment. In the first place, we ought to investigate its dependency upon the preceding links of the particular chain of life, varieties being often merely types or approximations of former parentage; thence the variation of the family, as well as of the individual, must be embraced by our experiments.