It behooves us, then, having found any faculty to be innate, not to rest content there, but steadily to follow backwards the line of causation, and thus to display, if possible, its manner of origin. This is the more necessary with the lower animals, where so much is innate.
The special laws of inheritance are indeed as yet unknown. All which is clear, and all which is to my purpose is, that there is a tendency, a probability, greater or less according to circumstances, but always considerable, that the descendants of cultivated parents will have, by born nervous organization, a greater aptitude for cultivation than the descendants of such as are not cultivated; and that this tendency augments, in some enhanced ratio, for many generations.
I do not think any who do not acquire -- and it takes a hard effort to acquire -- this notion of a transmitted nerve element will ever understand "the connective tissue" of civilization. We have here the continuous force which binds age to age, which enables each to begin with some improvement on the last, if the last did itself improve; which makes each civilization not a set of detached dots, but a line of colour, surely enhancing shade by shade.
