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The Struggle for Existence
Evolution and its Future
adapted advantage amount beak become bees believe best chance birds branches breed chapter climate closely common parent competition complex confined cross degree destroyed diagram distinct genera distinct species divergence of character diversified domestic doubt effect eggs exterminated extinct extremely facts favourable variations females fertilisation fertility flower to flower forms fossil genus geological periods gradations greater number groups habits Hence hermaphrodites humble-bees important increase in number independently created individuals inhabitants inherited insects instance instincts intercrossing intermediate intervals large number less improved living males manner modifica modified descendants natural selection naturalists nectar occasional offspring organic origin of species physical conditions pistil places pollen preservation prey principle probably produced progenitor quadruped red clover relations represented seedlings seeds self-fertilisation sexes sexual selection Silurian slight slowly stamens stigma structure struggle for existence successive supplant supposed tend terrestrial animals theory of descent tion tree variability vary well-marked varieties widely