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THE POPULAR SCIENCE MONTHLY 



culiarities, necessarily common to two fami- 

 lies whose modes of life are so exactly analo- 

 gous. No better practical specimen of the 

 new biological methods than that afforded 

 by this essay could possibly come into the 

 hands of readers with good common-sense 

 and little special scientific knowledge. 



The fifth and sixth essays, on " The 

 Colors of Animals and Sexual Selection," 

 and on " The Colors of Plants and the 

 Origin of the Color-Sense," lead us at once 

 into the region of controversy. They ap- 

 peared originally in MacmillarCs Magazine, 

 but they have since been enriched by nu- 

 merous additions and alterations, in accord- 

 ance with suggestions from Mr. Darwin or 

 other correspondents. In the first of these 

 two papers, Mr. Wallace brings a powerful 

 battery to bear against the accepted doctrine 

 of sexual selection, and it must be confessed 

 not without effect in shaking, if not in de- 

 molishing, that stronghold of Darwinism. 

 He contends that color is a natural product 

 of organic forms, which may be checked or 

 intensified by natural selection, but whose 

 occurrence is quite normal, and so stands in 

 need of no separate explanation. All col- 

 ors in animals may be classified under four 

 heads protective colors, warning colors, 

 sexual colors, and typical colors. The two 

 former do not now require further definition ; 

 but sexual differences of hue he attributes 

 not to conscious selection of mates, the 

 occurrence of which is emphatically doubted, 

 but to. a special necessity for concealment 

 in one or other sex ; as, for example, in the 

 incubating females of birds, or in the males 

 among those species in which that sex un- 

 dertakes the duty of hatching. This ex- 

 planation would refer the variety in color- 

 ing to natural selection alone, acting un- 

 equally upon the several sexes, and so caus- 

 ing a partial suppression of bright tints. 

 The vast majority of animal markings Mr. 

 Wallace attributes to typical coloring ; that 

 is to say, a conventional or meaningless dis- 

 tribution of pigment, serving mainly for 

 purposes of recognition between the mem- 

 bers of the same species. Though it would 

 be rash too readily to accept or reject these 

 careful and well-reasoned conclusions, it 

 seems probable that an intermediate belief 

 will ultimately prevail. Certainly, Mr. Wal- 

 lace has shown beyond a doubt that natural 

 selection will adequately and simply account 



for many curious phenomena which Mr. 

 Darwin believed to be due to conscious 

 preference. The partial elimination of this 

 markedly Lamarckian element in the theory 

 of descent cannot but be regarded as a dis- 

 tinct gain, though few readers will be in- 

 clined entirely to agree with the author in 

 his total rejection of sexual selection. 



The sixth essay applies the same general 

 principles to the colors of plants, and con- 

 tains some interesting speculations on the 

 beauty of Alpine flowers, and on the differ- 

 ence between succulent fruits and nuts. It 

 also touches briefly on the question of the 

 development in insects and vertebrates of a 

 faculty for the perception of colors, with re- 

 marks upon the theories lately advanced by 

 Geiger, Magnus, and Gladstone. This and 

 the succeeding paper are chiefly noticeable 

 for their exposition of the author's opinions 

 upon certain ultimate teleological questions. 

 In his book upon the Malay Archipelago, 

 Mr. Wallace advocated the belief that all 

 the beauty of the external world was due to 

 natural causes, without any divine after- 

 thought as to its effects upon the human 

 mind. But, since that time, the implications 

 contained in the doctrine of evolution seem 

 to have clashed with earlier prejudices, and 

 driven this otherwise acute and vigorous 

 thinker into a coquetry with so-called spir- 

 itualism, which has vitiated much of his 

 later work. In the present volume he sug- 

 gests that the colors of the organic world, 

 though developed by ordinary laws, may 

 have been specially directed by some supe- 

 rior agency with reference to the final en- 

 joyment of their beauty by man. In short, 

 he inclines to the purely gratuitous suppo- 

 sition that butterflies, birds, and flowers, ac- 

 quired brilliant tints in the Secondary and 

 Tertiary periods, partly in order that men 

 might look upon them in the Quaternary. 

 And the essay which we are now consider- 

 ing concludes with the ominous sentence, 

 " The emotions excited by color and by 

 music, alike, seem to rise above the level or 

 a world developed on purely utilitarian prin- 

 ciples." It is greatly to be regretted that 

 the joint discoverer of the theory of natural 

 selection should allow himself to make use 

 of such painfully dyslogistic and unscientific 

 language. 



The seventh essay, the presidential ad- 

 dress, bears the title of " By-paths in the Do- 



