Truer notions of genetic physiology are given by the Hebrew expression "seed". If we speak of a man as "of the blood-royal" we think at once of plebe… - William Bateson

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.

Of the contributions made during the essayist period three call for notice: Weismann deserves mention for his useful work in asking for the proof that "acquired characters" or, to speak more precisely, parental experience can really be transmitted to the offspring. The ocurrence of progressive adaptation by transmission of effects of use had seemed so natural to Darwin and his contemporaries that no proof of the physiological reality of the henomenon was thought necessary. Weismann's challenge revealed the utter inadequacy of the evidence on which the beliefs were based. They are doubtless isolated observations which may be interpreted as favouring the belief in these transmissions, but such meagre indications as exist are by general consent admitted to be too slight to be of much assistance in the attempt to understand how the more complex adaptive mechanisms arose.

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.