Evolution / by Patrick Geddes and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1911?]
Catalogue details

Licence: Public Domain Mark

Credit: Evolution / by Patrick Geddes and J. Arthur Thomson. Source: Wellcome Collection.

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    it will tend to re-establish itself, but if the range is overpassed, it will topple over into a new position; also that both of them are more likely to topple over towards the posi¬ tion of primary stability than away from it.” The Mutation Theory.—In 1900 Professor Hugo de Vries of Amsterdam published under the title 44 The Mutation Theory ” an account of his very interesting and important experi¬ ments and observations on the origin of species in the vegetable kingdom. The most striking of his conclusions was that species arise from one another by discontinuous leaps and bounds, as opposed to a continuous process. Whereas Darwin relied on the action of selection on minute individual variations or fluctuations, de Vries believes that these have nothing to do with the origin of species, which appear 44 all at once ” by mutations. Let us quote some of his characteristic state¬ ments. 44 By the mutation theory I mean the proposition that the attributes of organisms consist of distinct, separate and independent units. These units can be associated in groups, and we find, in allied species, the same units and groups of units. Transitions, such as we so frequently meet with in the external form both of animals and plants, are as