Includes bibliographical references and index.

Natural selection. Preamble to natural selection ; Variation under domestication ; Variation under nature I ; The struggle for existence ; Natural selection I ; Laws of variation ; Evolution today : a modern perspective on natural selection -- Speciation. Preamble to speciation ; Variation under nature II ; Natural selection II ; Hybridism ; Evolution today : the mosquitoes of the London underground -- Theory. Preamble: What is a theory? ; Difficulties on theory ; Instinct ; Geology I: Background ; Geology II: On the imperfection of the geological record ; Geology III: On the geological succession of organic beings ; Geology IV: Evolution today ; Geographical distribution ; Geographical distribution, continued ; Mutual affinities of organic beings : morphology: embryology: rudimentary organs ; Recapitulation and conclusion ; Evolution today : the witness has been found, again and again.