xii DOMESTICATED ANIMALS AND PLANTS 



CHAPTER PAi 



V. The Way of the Wild 50 



The astonishing abundance of life — The struggle for exist- 

 ence — Selective effect of the natural conditions — Competition 

 for food — Competition for room — Competition most severe 

 between individuals of the same species — Natural selection — 

 Survival of the fittest — The individual and the race — Signifi- 

 cance of numbers — Significance of vigor and length of life — 

 Significance of offensive and defensive weapons — Significance 

 of protective coloring and markings — Mimicry — Design in 

 nature — Causes of color in animals and plants 



VI. Effect of Natural Selection 83 1 



Natural selection means progressive development — Effect of I 



selection upon the individual — Selection good for the species 

 that can endure it — Selection fatal to a race that cannot en- 

 dure its hardships — Interest of the individual and the race 

 not identical — A close fit between a species and its environ- 

 ment is inevitable — Apparent exceptions due to absence of 

 severe selection — Adaptation not necessarily perfect — Our 

 standards of selection differ from those of nature — Not all the 

 results of natural selection are useful to us — Our standards 

 often require much readjustment of domesticated species — 

 Natural selection always at work — Power of selection to 

 modify type 



VII. Unit Characters 98 



Unit of study — Species composed of definite characters — 

 Every individual possesses all the characters of the race — 

 Characters developed and characters latent — Characters 

 dominant and. characters recessive — Correlation of characters 

 — Lost characters — New characters — Characters and unit 

 characters 



VIII. Variability of a Single Character 105 



Critical study of a single character — Types — Plotting the 

 frequency curve — The mean — The typical individual — Vari- 

 ability or deviation from type — Average deviation — Standard 

 deviation — Coefficient of variability — Suggestions as to tak- 

 ing measurements — Suggestions as to grouping — Sugges- 

 tions as to numbers — Suggestions as to taking samples — 

 Advantages of statistical studies 



IX. How Characters are Transmitted 121 



Every species of its own kind — The machinery of transmis- 

 sion — Fertilization — Fertilization in general — The material 

 transmitted — Chromosomes — Development, or growth and 

 differentiation — Termination to growth 



X. When Development goes Wrong 130 



Differentiation with development — Underdevelopment, or 

 dwarfing — Overdevelopment, or giants — Arrested develop- 

 ment of a single character or part — Overdevelopment of a 

 single part — Doubling of parts — Fusing of parts — When 

 unit characters get misplaced — Abnormal growths 



