The mutations of opinion on the subject during the last fifty years have been remarkable.
Bit by bit mutations are added to each other in different single characters until a sum or degree of mutations is reached which no zoologist would hesitate to place in a separate species or in a separate genus.
A due appreciation of the far-reaching results of " correlated variation " must, it appears, give a new and distinct explanation to the phenomena which are referred to as " large mutations," " discontinuous variation " and " saltatory evolution."
Professor Flinders Petrie, in his Huxley Lecture for 1906 on Migrations (reprinted by the Anthropological Institute), deals with the mutations and movements of races from an anthropological standpoint with profound knowledge and originality.
He proposed the term " mutations " for the minute progressive changes of single characters in definite directions as observed in successive stratigraphic levels.
More recent analysis has shown, however, that certain modifications observed within the same stratigraphic level are really grades of mutations which show divergences comparable to those found in successive levels.
He also demonstrated that mutations have this special or distinctive character, that they repeat in the same direction without oscillation or retrogression.
Huxley questioned the time value of fossils, but recent research has tended to show that identity of species and of mutations is, on the whole, a guide to synchroneity, though the general range of vertebrate and invertebrate life as well as of plant life is generally necessary for the establishment of approximate synchronism.
Such gradations, termed " mutations " by Waagen, are distinguished, as observed, in single characters; they are the xx.
The mutations of Waagen may possibly, in fact, prove to be identical with the " definite variations " or " rectigradations " observed by Osborn in the teeth of mammals.
The essence of Waagen's law is orthogenesis, or evolution in a definite direction, and, if there does exist an internal hereditary principle controlling such orthogenetic evolution, there does not appear to be any essential contradiction between its gradual operation in the " mutations of Waagen " and its occasional hurried operation in the " mutations of de Vries," which are by their definition discontinuous or saltatory (Osborn, 1907).
It should be remembered that palaeontology is the most unfavourable field of all for observation and demonstration of sudden saltations or mutations of character, because of the limited materials available for comparison and the rarity of genetic series.
De Vries gave the name "mutations" to such considerable variations (it is to be noted that a further concept, that of the mode of origin, has been added to the word mutation, and that the conception of relative size is being removed from it), and Bateson, de Vries and other writers have added many striking cases to those recorded by Darwin.
Even amongst the extreme advocates of the theory of mutations, the importance of magnitude is being discounted by their suggestion that some of the minute variations which have hitherto been regarded by them as insignificant "fluctuating variations" may be significant mutations.
The variations which de Vries has called mutations, and which were at first associated by Bateson with what he called discontinuous variations as the exclusive source of new species, are now supposed by de Vries to be distinguished from fluctuating variations by their mode of origin.
And finally, there are a series of variations, amongst which no doubt are the mutations of de Vries and the disintegrations and recombinations of the unit factors with which Mendel and his followers have worked, in which the external or environmental factor is most remote from the actual result.
If the first order of genetic modification is deliberately keeping desirable mutations, then this is the second order: creating conditions for such genetic modifications to occur more rapidly.
From this fundamental difference between the view held by history and that held by jurisprudence, it follows that jurisprudence can tell minutely how in its opinion power should be constituted and what power-- existing immutably outside time--is, but to history's questions about the meaning of the mutations of power in time it can answer nothing.