CONTENTS. IX 



CHAPTER XX. 



THEOEIES OF PROGRESSION AND TRANSMUTATION. 



Antiquity and Persistency in Character of the existing Eaces of Mankind — 

 Theory of their Unity of Origin considered — Bearing of the Diversity of 

 Races on the Doctrine of Transmutation — Difficulty of defining the Terms 

 " Species" and " Race" — Lamarck's Introduction of the Element of Time into 

 the Definition of a Species — His Theory of Variation and Progression — 

 Objections to his Theory, how far answered — Arguments of modern Writers 

 in favor of Progression in the Animal and Vegetable World — The old 

 Landmarks supposed to indicate the first Appearance of Man, and of dif- 

 ferent Classes of Animals, found to be erroneous — Yet the Theory of an 

 advancing Series of organic Beings not inconsistent with Facts — Earliest 

 known Fossil Mammalia of low Grade — No Vertebrata as yet discovered in 

 the oldest fossiliferous Rocks — Objections to the Theory of Progression 

 considered — Causes of the Popularity of the Doctrine of Progression as 

 compared to that of Transmutation Page 385 



CHAPTER XXI. 



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 — Hypothesis of 

 definite and indefinite Modifiability equally arbitrary — Competition and 

 Extinction of Races — Progression not a necessary Accompaniment of 

 Variation — Distinct Classes of Phenomena which natural Selection exi^lains 

 — Unity of Type, rudimentary Organs, Geographical Distribution, Relation 

 of the extinct to the living Fauna and Flora, and mutual Relations of suc- 

 cessive Groups of Fossil Forms — Light thrown on Embryological Develop- 

 ment 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 — Sefstrbm on alternate Gene- 

 ration — How far the Doctrine of independent Creation is opposed to the 

 Laws now governing the Migration of Species 407 



CHAPTER XXII. 



OBJECTIONS TO THE HYPOTHESIS OF TRANSMUTATION CONSIDERED. 



Statement of Objections to the Hypothesis of Transmutation founded on the 

 Absence of intermediate Forms — Genera of which the Species are closely 

 allied — Occasional Discovery of the missing Links in a Fossil State — 

 Davidson's Monograph on the Brachiopoda — Why the Gradational Forms, 

 when found, are not accepted as Evidence of Transmutation — Gaps caused 

 by Extinction of Races and Species — Vast Tertiary Periods during which 

 this Extinction has been going on in the Fauna and Flora now existing — 



