The Origin of Species by Means of Natural Selection, Or The Preservation of Favoured Races in the Struggle for Life

accumulated adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells chapter characters climate closely allied color continent crossed crustaceans degree developed difficulty distinct species doubt effects eggs embryo existing extinct extremely facts favorable fertility flowers formation formerly forms fossil Fritz Müller Gärtner genera genus geological geological period Glacial period gradations greater number habits Hence hybrids important increase individuals inhabitants inherited insects instance instincts intercrossing kind larvae less living males mammals manner marsupial migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organs palaeozoic parent peculiar pedicellariae perfect pigeon pistil plants pollen present principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed tend theory tion trees variability variations vary whilst whole wings young