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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



ing more and more. In the history of the devel- 

 opment of living things, on the contrary, entire 

 confidence was reposed in the ancient and unten- 

 able myth, according to which every species of 

 animals or of plants was, like man himself, cre- 

 ated independently of every other species. These 

 creations, it was supposed, had succeeded to one 

 another in series, without any tie of filiation. This 

 flat contradiction of the two doctrines — the ge- 

 ologists' theory of natural development, and the 

 naturalists' myth of a supernatural creation— was 

 ended by Darwin in 1859 in favor of the former. 

 Since then we no longer make any difficulty about 

 believing that the formation and the transfor- 

 mation of the living things inhabiting our globe 

 obey the grand eternal laws of a mechanical evo- 

 lution, precisely like the earth itself and the whole 

 system of the universe. 



We no longer are required now, as was the 

 case fourteen years ago at the Stettin meeting of 

 the Congress of Naturalists, to gather together 

 proofs of the new theory of evolution founded by 

 Darwin. Since that time, the knowledge of that 

 truth has made most satisfactory progress. In 

 the field of research with which my own labors 

 are concerned, in the extensive science of organic 

 forms or morphology, it is everywhere recognized 

 as of the very highest importance, as basic. Com- 

 parative anatomy and embryology, systematic zo- 

 ology and botany, can no longer disregard the 

 theory of descent. It alone is able to explain the 

 mysterious relations of innumerable organic forms 

 to one another ; in other words, to refer them to 

 their mechanical causes. Their mutual resem- 

 blances are explained to be a natural conse- 

 quence, as being an inheritance from a common 

 ancestral form ; and their differences are ac- 

 counted to be the necessary effect of an adapta- 

 tion to different conditions of existence. By the 

 theory of descent alone can we explain, simply 

 and naturally, the facts of paleontology, of cho- 

 rology, and of oecology ; ! by its aid alone can we 

 account for those remarkable rudimentary organs 

 — eyes that see not, wings that do not fly, mus- 

 cles that do not contract — in a word, all those 

 useless parts of the body which so embarrass the 

 prevailing teleology. These organs clearly show 

 that conformity to an end, in the structure of or- 

 ganic forms, is neither general nor complete ; 

 they do not emanate from a plan of creation 

 drawn up beforehand, but were of necessity pro- 



1 Chorology treats of the geographical and topo- 

 graphical distribution of organisms ; oncology of the 

 habitations, the means of existence, and the mutual 

 relations of organisms. 



duced by the accidental clash of mechanical 

 causes. 1 



The man who, in the face of these imposing 

 facts, should still demand proofs in favor of the 

 theory of descent, would himself give evidence 

 only of one thing, namely, his lack of knowledge 

 and of understanding. To demand proofs exact 

 and strictly experimental "would be a totally dif- 

 ferent thing. Such a demand — and it is cften 

 made — results from a very wide-spread, errone- 

 ous idea, that all natural sciences may be exact 

 sciences. But the truth is, that only a small frac- 

 tion of the natural sciences is exact, namely, such 

 of them as are based on mathematics. These are, 

 first, astronomy, and, above all, the higher me- 

 chanics ; then the greater part of physics and 

 chemistry, as also a good deal of physiology, and 

 only a very small portion of morphology. In 

 the last-named department of biology the phe- 

 nomena are so complex, so variable, that, as a 

 rule with respect to them, the mathematical 

 method is out of the question. Though we may ) 

 as a broad principle, require for all sciences an 

 exact and even a mathematical basis, and though 

 the possibility of finding such a basis may be ad- 

 mitted, nevertheless, in nearly all the branches 

 of biology we are absolutely unable to comply 

 with this condition. Here the historical, the his- 

 torico-philosophical method is the best substitute 

 for the exact or physico-mathematical method. 



This is particularly true of morphology. In 

 truth, we attain scientific knowledge of organic 

 forms only through the history of their develop- 

 ment. The great progress of our times in this 

 branch of science comes from the fact that we 

 have extended the signification and the scope of 

 the history of development infinitely beyond the 

 limits it had before Darwin's day. Before his 

 time, that term was applied only to the develop- 

 ment of the organized individual, now styled em- 

 bryology or ontogeny. When the botanist traced 

 the plant to its seed, or the zoologist the animal 

 to the egg, they both supposed that with this 

 history of the embryo they had settled the whole 

 question of morphology. Our greatest embryolo- 

 gists, Wolff, Baer, Remack, Schleiden, and (till re- 

 cently) the whole school founded by them, knew 

 only of individual embryology. Nowadays, and 

 for us, the mysterious phenomena of embryology 

 are very different things. They are no longer 

 incomprehensible enigmas ; we grasp their pro- 

 found meaning. In obedience to the laws of 



1 Dysteleology treats of rudimentary organs ns con- 

 tradicting the " conformity to an end " of the support- 

 ers of teleology, or the doctrine of final causes. 



