Volume 1

Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation.

Shipley A. E. (Arthur Everett), Sir, 1861-1927.

Date:: 1891-1892

Credit: Essays upon heredity and kindred biological problems / by August Weismann ; edited by Edward B. Poulton, Selmar Schönland, and Arthur E. Shipley, authorized translation. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$writers started with the hypothesis that there must be a direct connexion between the germ-cells of succeeding generations, and they tried to establish such a continuity by supposing that the germ-cells of the offspring are separated from the parent germ-cell before the beginning of embryonic development, or at least before any histological differentiation has taken place. In this form their suggestion cannot be maintained, for it is in conflict with numerous facts. A continuity of the germ-celis does not now take place, except in very rare instances; but this fact does not prevent us from adopting a theory of the continuity of the germ-plasm, in favour of which much weighty common group and converge to a common contribution, because they were both evolved out of elements contained in a structureless ovum, and they, jointly, contribute the elements which form the structureless ova of their offspring.' The following diagram shows clearly 'that the span of each of the links in the general chain of heredity extends from one structureless stage to another, and not from person to person :— Structureless elements ( . . Adult Father . . ) structureless elements in Father ( . . Latent in Father . . | in Offspring.' Again Galton states—' Out of the structureless ovum the embryonic elements are taken . . . and these are developed {a) into the visible adult individual ; on the other hand . . ., after the embryonic elements have been segregated, the large residue is developed {b) into the latent elements contained in the adult individual.' The above quoted sentences and diagram indicate that Galton does not derive the whole of the hereditary tendencies from the latent elements, but that he believes some effect is also produced by the patent elements. When however he contrasts the relative power of these two influences, he attaches comparatively little importance to the patent elements. Thus if any character be fixed upon, Galton states that it 'may be conceived (i) as purely personal, without the concurrence of any latent equivalents, (2) as personal but conjoined with latent equivalents, and (3) as existent wholly in a latent form.' He argues that the hereditary power in the first case is exceedingly feeble, because ' the effects of the use and disuse of limbs, and those of habit, are transmitted to posterity in only a very slight degree.' He also argues that many instances of the supposed transmission of personal characters are really due to latent equivalents. ^ The personal manifestation is, on the average, though it need not be so in every case, a certain proof of the existence of latent elements ' Having argued that the strength of the latter in heredity is further supported by the facts of reversion, Galton considers it is safe to conclude ' that the contribution from the patent elements is very much less than from the latent ones.' In the later development of his theory Galton adheres to the conception of ' gemmules ' and accepts Darwin's views, although 'with considerable modification.' Together with pan- genesis itself, Galton's theory must be looked upon as preformational and so far it is in opposition to Weismann's theoiy which is epi^enetic bee Appendix IV. to the next Essay (V).—E. B. P ]$