The lower animals, on the other hand, must have their bodily structure modified in order to survive under greatly changed conditions. They must be rendered stronger, or acquire more effective teeth or claws, in order to defend themselves from new enemies; or they must be reduced in size so as to escape detection and danger. When they migrate into a colder climate they must become clothed with thicker fur, or have their constitutions altered. If they fail to be thus modified, they will cease to exist.
Charles DarwinIn my simplicity, I remember wondering why every gentleman did not become an ornithologist.
Charles DarwinNow when naturalists observe a close agreement in numerous small details of habits, tastes and dispositions between two or more domestic races, or between nearly-allied natural forms, they use this fact as an argument that all are descended from a common progenitor who was thus endowed; and consequently that all should be classed under the same species. The same argument may be applied with much force to the races of man.
Charles DarwinI am actually weary of telling people that I do not pretend to adduce [direct] evidence of one species changing into another, but I believe that this view is in the main correct, because so many phenomena can thus be grouped end explained.
Charles DarwinThere is no fundamental difference between man and animals in their ability to feel pleasure and pain, happiness, and misery.
Charles DarwinI conclude that the musical notes and rhythms were first acquired by the male or female progenitors of mankind for the sake of charming the opposite sex.
Charles DarwinI fully agree with all that you say on the advantages of Spencer's excellent expression of 'the survival of the fittest.' This, however, had not occurred to me till reading your letter. It is, however, a great objection to this term that it cannot be used as a substantive governing a verb; and that this is a real objection I infer from H. Spencer continually using the words, natural selection.
Charles Darwin