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 and after Darwin,’ delivered as Fullerian professor of physiology at the Royal Institution, a position which he held for three years (1888–91). The substance of these two courses of lectures was subsequently embodied in a treatise bearing the title of the Fullerian course, of which the first part was published in 1893; two other parts, completing the work, were left ready for publication at the time of his death. The first part deals with the ‘Darwinism of Darwin;’ the second part, which appeared with a portrait of the author in 1895, deals with those post-Darwinian problems which involve questions of heredity and utility; while the third part (at present unpublished) contains a discussion of the problems of isolation and of the author's theory of ‘physiological selection.’ This theory, which was regarded by Romanes as his chief substantive contribution to evolutionary doctrine, was first propounded by him in a paper contributed to the Linnean Society in 1886, the full title of which was ‘Physiological Selection: an Additional Suggestion on the Origin of Species.’ The suggestion is briefly as follows. It was part of the body of biological doctrine that when a group of animals or plants belonging to any species is isolated by geographical barriers, that group tends, under the influence of its specialised environment, to develop characters different from those of the main body of the species from which it is isolated. Eventually the divergence of characters may proceed so far as to render the isolated group reciprocally sterile with the original species, and thus to render it not only morphologically but also physiologically a distinct species. Romanes, in his Linnean paper, suggested that reciprocal sterility between individuals not otherwise isolated may be the primary event, the cause and not the effect; and that in this way a physiological barrier may be set up between two groups of the individuals originally belonging to one species and inhabiting the same geographical area. The essential feature of the suggestion is that this physiological barrier may be primary and not secondary. The title of the paper was unfortunate. ‘Physiological Isolation’ would have indicated the author's contention more accurately than ‘Physiological Selection,’ and would perhaps have more effectually guarded him from the attacks of those who charged him with the intention of substituting a new doctrine of the origin of species for that which was associated with the name of Darwin. The paper, which gave rise to much controversy, was unquestionably speculative, and the main contention was not supported by a sufficient body of evidence to carry conviction.

As early as 1874 Romanes suggested in letters to ‘Nature’ what he termed ‘the principle of the cessation of selection.’ He argued that since organs are maintained at a level of maximum efficiency through natural selection, the mere withdrawal or cessation of selection will lead to diminution and degeneration of organs. He distinguished this ‘cessation of selection’ from ‘reversal of selection’ where such diminution or degeneration is, through ‘the principle of economy of growth’ or otherwise, advantageous, and therefore promoted by natural selection. When Weismann advocated panmixia, which includes the effects of both cessation and reversal of selection, Romanes reiterated his former contention (Nature, 1890, xli. 437), and returned to the subject in ‘Darwin and after Darwin’ (vol. ii.) The matter has given rise to some discussion. It would seem that, though the cessation of selection may reduce the level of efficiency of an organ from the maximum maintained by natural selection to the mean efficiency in the individuals born subsequently to the withdrawal of the eliminative influence, it cannot reduce it in any marked degree unless we call in a further ‘principle’ of the failure of heredity. That the mere cessation of selection cannot of itself lead to great reduction was shown by Darwin before Romanes's letters were published (cf. Origin of Species, 6th edit. pp. 401–2).

With regard to the vexed question of the inheritance of acquired characteristics, Romanes lent the weight of his support to the Lamarckian side, but he constantly sought to put the matter to the test of experiment.

Romanes's ‘Essay on Christian Prayer and General Laws,’ which won the Burney prize at Cambridge in 1873, necessarily pursued the lines of orthodox apologetics; but there is no reason to suppose that it did not in the main indicate the author's own views at the time when it was written. But when he issued in 1878, under the pseudonym of ‘Physicus,’ a work entitled ‘A Candid Examination of Theism,’ he assumed towards orthodox religious beliefs a negative and destructive attitude. Powerfully written, and showing much dialectic skill, the ‘Candid Examination’ made some stir both in the orthodox and the unorthodox camps. But five years later Romanes struck another note in an article in the ‘Nineteenth Century’ on ‘The Fallacy of Materialism’ (1882); while in the Rede lecture, which he was chosen to deliver in Cambridge in 1885, he