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Capítol VII. Miscellaneous Objections to the Theory of Natural Selection. | |
| Longevity — Modifications not necessarily simultaneous — Modifications apparently of no direct service — Progressive development— Characters of small functional importance, the most constant — Supposed incompetence of natural selection to account for the incipient stages of useful structures — Causes which interfere with the acquisition through natural selection of useful structures — Gradations of structure with changed functions — Widely different organs in members of the same class, developed from one and the same source — Reasons for disbelieving in great and abrupt modifications | 168-204 |
Capítol VIII. Instinct. | |
| Instincts comparable with habits, but different in their origin — Instincts graduated — Aphides and ants — Instincts variable — Domestic instincts, their origin — Natural instincts of the cuckoo, molothrus, ostrich, and parasitic bees — Slave- making ants — Hive-bee, it's cell-making instinct — Changes of instinct and structure not necessarily simultaneous — Difficulties of the theory of the Natural Selection of instincts — Neuter or esterile insects — Summary | 205-234 |
Capítol IX. Hybridism. | |
| Distinction between the sterility of first crosses and of hybrids — Sterility various in degree, not universal, affected by close interbreeding, removed by domestication — Laws governing the sterility of hybrids — Sterility not a special endowment, but incidental on other differences, not accumulated by natural selection — Causes of the sterility of first crosses and of hybrids — Parallelism between the effects of changed conditions of life and of crossing — Dimorphism and trimorphism — Fertility of varieties when crossed and of their mongrel offspring not universal — Hybrids and mongrels compared independently of their fertility — Summary | 234-263 |
