CONTENTS 



Architectural Changes in the Chromosomes 216 



Position Effects 219 



The Bar Eije "Gene" 219 



Chromosomal Rearrangements Differentiating Species 221 



Overlapping Inversions and Phijlogeny 222 

 The Architecture of the Chromosomes and Systemic Mutation 224 



Functional Organization of the Chromosome 225 



Difficulties of Neo-Darwinism 227 

 References 229 



PART FOUR: THE ORIGIN OF SPECIES 

 AND OF HIGHER CATEGORIES 231 



Chapter Fifteen: Natural Selection 233 



Severe Versus Mild Selective Forces 233 

 Experimental Demonstration of Natural Selection 234 

 Observed Changes in Natural Populations 236 



Industrial Melanism 236 



Additional Examples 237 



Polymorphism 237 

 Adaptive Resemblances 240 



Cryptic Coloration 240 



Warning Coloration 243 



Mimicry 244 



The Reaction against Protective Coloration 246 



Resolution of Difficulties 247 

 Sexual Selection 249 

 Selection and Nonadaptive Characters 250 



Cooperation and Selection 251 

 References 252 



Chapter Sixteen: Some Quantitative Aspects of Evolution 253 



Evolutionary Mathematics 253 



The Hardy-Weinberg Law 253 



Selection Pressure and Rates of Evolution 255 



Mutation Pressure and Genetic Equilibrium 256 



Population Size and the Effectiveness of Selection 258 



Genetic Drift, the Sewall Wright Effect 258 



Allometry 261 

 References 262 



Chapter Seventeen: Continuous Versus Discontinuous Variation 263 



The Bases of Discontinuous Variability 263 



Permutation of Genes 264 

 The Species Concept 264 



Magnitude of Difference 265 



Discontinuity and Interspecific Sterility 265 



Rassenkreise and Speciation 267 

 References 269 



Chapter Eighteen: Isolating Mechanisms and Species Formation 270 



Mendelian Genetics, Isolation, and Subspeciation 270 

 Isolating Mechanisms 271 



Restriction of Random Dispersal 272 



Restriction of Random Mating 274 



xo 



