By George Gamow
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The former seems to be much the more important; for nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform. The effects on the offspring are either definite or in definite. They may be considered as definite when all or nearly all the offspring of individuals exposed to certain conditions during several generations are modified in the same manner. It is extremely difficult to come to any conclusion in regard to the extent of the changes which have been thus definitely induced.
He believes, like Dean Herbert, that species, when nascent, were more plastic than at present. He lays weight on what he calls the principle of finality, "puissance mysterieuse, indeterminee; fatalite pour les uns; pour les autres volonte providentielle, dont l'action incessante sur les etres vivantes determine, a toutes les epoques de l'existence du monde, la forme, le volume, et la duree de chacun d'eux, en raison de sa destinee dans l'ordre de choses dont il fait partie. " (From references in Bronn's "Untersuchungen uber die Entwickelungs-Gesetze", it appears that the celebrated botanist and palaeontologist Unger published, in 1852, his belief that species undergo development and modification.
There can, however, be little doubt about many slight changes, such as size from the amount of food, colour from the nature of the food, thickness of the skin and hair from climate, etc. Each of the endless variations which we see in the plumage of our fowls must have had some efficient cause; and if the same cause were to act uniformly during a long series of generations on many individuals, all probably would be modified in the same manner. Such facts as the complex and extraordinary out growths which variably follow from the insertion of a minute drop of poison by a gall-producing insect, shows us what singular modifications might result in the case of plants from a chemical change in the nature of the sap.
A Planet Called Earth by George Gamow