NA TURE 



341 



THURSDAY, FEBRUARY 7, 1901. 



A NEO-DARWINIAN ON EVOLUTION. 

 Problems of Evolution. By F. W. Headley. Pp. xvi + 



ni. (London: Duckworth and Co., 1900.) 

 A yf UCH of the work that has lately appeared on the 

 ■L» i subject of organic evolution has been character- 

 ised, if not by a misapprehension of the main points at 

 issue, at any rate by a want of due proportion in the 

 treatment of data, and by a tendency to build an elaborate 

 superstructure on a very slender foundation of fact. This 

 applies less to the work of English authors than to those' 

 of other countries. It is satisfactory to find that English 

 men of science, who have always taken a leading part in 

 the promotion of sound and rational views on the methods 

 of evolution, are still distinguished by the thoroughness 

 and good sense which they bring to bear on the dis- 

 cussion of evolutionary problems. 



Mr. Headley's book is on the whole a favourable 

 example of this kind of literature. It is true that his' 

 statements of fact are not always free from error, nor are 

 his arguments on all points convincing ; he shows, 

 nevertheless, a just appreciation of the difficulties of the 

 subject and a wide acquaintance with the various attempts 

 that have been made towards their solution, while his 

 own suggestions have been well considered, and are 

 often of distinct value. His standpoint is more thoroughly 

 Darwinian than that of many other recent writers, and in 

 him the principle of natural selection as the most im- 

 portant factor in evolution finds a powerful and skil- 

 ful advocate. He is an uncompromising opponent of 

 Lamarckism, and one of the most satisfactory sections of 

 the book is that in which he shows how completely the 

 Lamarckian principle fails to account for those very 

 phenomena which have been most confidently appealed 

 to in its support. This, however, does not preclude 

 him from recognising the importance of the suggestion 

 made independently by Profs. Mark Baldwin and Lloyd 

 Morgan, viz., that the selection value imparted to a con- 

 genital variation by exercise may enable such variation 

 to become the starting-point for other variations in the 

 same direction (Darwin's "Continuity of Variation"). 

 Not only does he adopt the principle in the form here 

 stated, but he goes on to show that parental care and the 

 gregarious habit may act in a similar way by promoting 

 the survival of certain characters which can be increased 

 by practice, and so giving an opportunity for their 

 enhancement, by further variation, in successive genera- 

 tions. But he rightly points out that this cannot properly 

 be claimed by Lamarckians as a concession to their 

 views ; those who would so claim it must have, as he 

 says, "a singular power of mistaking an utter rout for 

 a compromise." For, as Prof. Lloyd Morgan makes 

 clear, there is here "no transmission of modifications 

 due to individual plasticity " ; and what really emerges 

 is that natural selection is capable, without such trans- 

 mission, of doing all that was exclusively claimed on 

 behalf of Lamarckism. 



On the defensive side, Mr. Headley makes a forcible 

 use of the phenomena of adaptation. He has little to 

 bring forward that is actually new on this head, but his 

 NO. 1632, VOL. 63I 



statement of the case is a clear and cogent one. The 

 principle of recognition marks is acknowledged by him 

 as supplying the key to many instances of apparently 

 useless characters, and this line of argument might 

 profitably have been expanded. He is on strong ground 

 when asserting the importance of slight points of 

 difference. 



" Two races are brave beyond dispute, but one will 

 stand a little longer under fire than the other, and it is 

 this little that makes all the difference in the struggle. 

 Two young men are about on a par, and seem likely to 

 run neck and neck in the race of life, but an almost im- 

 perceptible superiority in one seems to act with cumu- 

 lative effect, and in twenty years, say, he is miles ahead." 



The latter illustration will appeal to most readers with 

 experience of life. 



The author's treatment of the important subject of 

 variation is interesting and suggestive. True to his 

 anti-Lamarckian principles, he denies any direct influence 

 of the environment on the origin of variations properly 

 so-called: "An external condition can do nothing but 

 bring to light some quality" already latent. To explain 

 the variations among offspring we must fall back on the 

 doctrine of the continuity of the germ-plasm coupled 

 with the specialising effect of cell-division. 



"When fission takes place, inequality must result. . . . 

 There is a thorough shuffling of the cards before they 

 are cut." 



This view is to some extent akin to Weismann's earlier 

 position as to the import of reducing divisions and am- 

 phimixis. But the author goes further than Weismann. 

 Not only have the reducing divisions of the germ-cells in 

 the metazoa the value of an incipient specialisation, but 

 the simple fissions of the protozoa have precisely the 

 same significance. Over-speciaHsation, such as would 

 in many cases result from a process of fission indefinitely 

 continued, is a cause of failure and death. This in the 

 bulk of the protozoa, at all events, is counteracted by 

 periodical conjugation, which tends to restore to each 

 cell some elements which it had lost, or was in process of 

 losing, by repeated fission. Amphimixis in the metazoa 

 has a similar role. Hence both fission and conjugation, 

 or amphimixis, are a cause of variation, though the latter, 

 while increasing the possibilities of deviation, tends to 

 prevent it from taking a harmful direction. An obvious 

 criticism on this view is that two imperfect organisms do 

 not necessarily make a perfect one. The speculation, 

 nevertheless, is ingenious and interesting, even though 

 it may fail to convince. 



In a further discussion of that perfection of adaptation 

 which almost appears to call for a '' directive force " pre- 

 siding over variation, he takes occasion to give an account 

 of Prof. Weldon's application of the law of chance. The 

 argument is fairly stated, but in his comments upon it 

 Mr. Headley seems disposed to blame Prof. Weldon's 

 results for not clearing up points with which they were 

 never intended to deal. His criticism is thus somewhat 

 beside the mark, for, as he himself admits. Prof Weldon's 

 aim was chiefly to demonstrate the high probability of 

 advantageous variations affecting a large number of 

 individuals at the same time, in this way affording abun- 

 dant material for selection. The question why variation 

 should take one direction more than another belongs to 



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