CHAP. XXI. ORIGIN OF SPECIES. 407 



CHAPTER XXL 



ON THE ORIGIN OF SPECIES BY VARIATION AND NATURAL 



SELECTION. 



MR. Darwin's theory of the origin of species by natural 



SELECTION memoir BY MR. WALLACE MANNER IN WHICH FAVORED 



RACES PREVAIL IN THE STRUGGLE FOR EXISTENCE FORMATION OF 



NEW RACES BY BREEDING — HYPOTHESES OF DEFINITE AND INDEFINITE 

 MODIFIABILITY EQUALLY ARBITRARY — COMPETITION AND EXTINCTION 



OF RACES PROGRESSION NOT A NECESSARY ACCOMPANIMENT OP 



VARIATION DISTINCT CLASSES OF PHENOMENA WHICH NATURAL 



SELECTION EXPLAINS UNITY OF TYPE, RUDIMENTARY ORGANS, GEO- 

 GRAPHICAL DISTRIBUTION, RELATION OF THE EXTINCT TO THE LIVING 

 FAUNA AND FLORA, AND MUTUAL RELATIONS OF SUCCESSIVE GROUPS 



OF FOSSIL FORMS LIGHT THROWN ON EMBRYOLOGICAL DEVELOPMENT 



BY NATURAL SELECTION WHY LARGE GENERA HAVE MORE VARIABLE 



SPECIES THAN SMALL ONES DR. HOOKER ON THE EVIDENCE AFFORDED 



BY THE VEGETABLE KINGDOM IN FAVOR OF CREATION BY VARIATION 



SEFSTROM ON ALTERNATE GENERATION HOW FAR THE DOCTRINE 



■ OF INDEPENDENT CREATION IS OPPOSED TO THE LAWS NOW GOVERN- 

 ING THE MIGRATION OF SPECIES. 



TT^OE many years after the promulgation of Lamarck's doc- 

 -■- trine of progressive development, geologists were much 

 occupied with the question whether the past changes in the 

 animate and inanimate world were brought about by sudden 

 and paroxysmal action, or gradually and continuously, by 

 causes differing neither in kind nor degree from those now in 

 operation. 



The anonymous author of " The Vestiges of Creation" pub- 

 lished in 1844 a treatise, written in a clear and attractive 

 style, which made the English public familiar with the lead- 

 ing views of Lamarck on transmutation and progression, but 

 brought no new facts or original line of argument to sup- 



27 



