560 



SCIENCE. 



[Vol. VIII., No. 203 



DR. WALLACE ON THE DEVELOPMENT 

 THEORY. 



Dr. Alfred Russell Wallace, the distin- 

 guished evolutionist, delivered four lectures in the 

 lecture course of the Peabody institute in Balti- 

 more on Nov. 30, Dec. 2, 7, and 9. His general 

 subject was ' The development theory and protec- 

 tive coloring.' The first lecture was devoted to a 

 general outline of the Darwinian movement. The 

 lecturer began by calling attention to a circum- 

 stance which he thought was too often neglected 

 in evolutionary discussions ; namely, the notions 

 as regards species that existed before Darwin. At 

 that time the fixity of species was regarded as an 

 incontrovertible fact ; and the origin of them, 

 when explained at all, was referred to independ- 

 ent acts of creation. It is only by contrasting 

 present zoological notions with the ones just men- 

 tioned that the immensity of Darwin's influence 

 wiU be fully appreciated. It is true that before 

 him a few writers had been bold enough to ques- 

 tion the validity of the theory of the fixity of 

 species. Foremost among them were Lamarck, 

 Chambers, the author of the 'Vestiges of crea- 

 tion,' and others. But what was lacking in the 

 speculations of these writers, and the reason why 

 they were not as widely read as Darwin, was that 

 they failed to produce any motive power sufficient 

 to cause the transformation of species, and were 

 not sufiiciently acquainted with the facts that 

 would suggest such a power. This was the distinc- 

 tive work of Darwin, and through this the theory 

 bears his name. 



There are three main principles derived from 

 the facts of nature from which the Darwinian 

 theory and its consequences follow as an inference. 

 The first of these is the high rate of multiplica- 

 tion of animal life, which makes it impossible for 

 all the offspring to be sustained, and thus creates 

 a necessary struggle for existence among them- 

 selves and with other animal forms. The inten- 

 sity of this struggle depends on the rate of multi- 

 plication of the animal in question ; and, when 

 that is great, the life-period will be short, and the 

 number who live to maturity correspondingly 

 small. To appreciate how severe this struggle is, 

 it may be mentioned that if a pair of partridges, 

 a single species of birds, live for sixteen years, ;and 

 breed, as they do, about eighteen young, and all 

 these were to live and multiply at the same rate, 

 then at the end of the sixteen years the whole sur- 

 face of the earth, land and water, would not be 

 sufficient to give all the partridges standing-room. 



The second important principle is furnished by 

 the variability of all parts of living tissue. It is 

 difficult to appreciate the extent of this variation. 

 Only by accurate measurements can it be realized 



that the variation within species is by no means as 

 small or insignificant as is often supposed. The 

 published writings of Darwin deal more with the 

 evidences of artificial variation than of that in a 

 state of nature. But evidences of the extreme varia- 

 bility of natural species are abundant. Diagrams 

 representing the variation in the size of the chief 

 parts of the body of specimens of several species 

 of birds, of squirrels, and so on, were exhibited, 

 and pictured not only the extent of this variation, 

 but the independence of the variation in one part 

 of that in another. Each part varies independent- 

 ly. It was shown, too, that while the ordinary 

 probability curve represents the natural variation 

 of an organ, the curve must be flat and long 

 drawn out to express the extreme limits of varia- 

 tion and the comparatively slight tendency to- 

 wards extreme crowding about the average form. 

 •With these facts we pass to the third main 

 principle, the hereditary character of these varia- 

 tions. The offspring of parents with similar varia- 

 tions will tend to preserve them ; and the (though 

 not the exclusive one, as Darwin knew) motive 

 power which selects certain variations for preserva- 

 tion by hereditary transmission, and consigns the 

 rest to oblivion, is natural selection. Those varia- 

 tions most in accord with the environment, best 

 adapted to succeed in the struggle for existence, 

 will survive as the fittest. To the objection that 

 such favorable variations would be overshadowed 

 by the other variations all with equal hereditary 

 tendency, the answer was given that variation 

 was sufficiently universal to insure the variation 

 of many individuals in a similar direction, though 

 in less degree, at any time. All variations are ly- 

 ing latent in the background, ready to assert them- 

 selves when the environment gives them an op- 

 portunity. The great rapidity of this change is 

 shown in those cases where man makes artificial 

 selections, and causes any part of a plant, for in- 

 stance, which happens to be edible by him, to ex- 

 hibit the greatest variability in size, nutrition, 

 taste, and all else. 



In conclusion, the lecturer expressed the view 

 peculiar to himself, that the human mind is ex- 

 cluded from this evolution from more lowly 

 forms, and that the belief in the gradual develop- 

 ment of man's body is in no wise inconsistent with 

 the belief that his soul springs from a higher 

 source, and should yield to all those aspirations 

 Avhich religion is intended to satisfy. 



In the second lecture. Dr. Wallace confined him- 

 self to the consideration of one of the devices by 

 which animals rendered themselves the more fit 

 to survive. This consists in adapting themselves 

 to their environment by imitating it. The object 

 of such imitation is primarily to escape observa- 



