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Its bearing on natural selectionThe term used in a wide sense
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according action adapted admit allied America amount animals appear become believe belonging birds breeds called cause certain characters climate closely common considered continued crossed descended developed difficulty distinct domestic doubt effects existing extinct extremely facts families favourable fertility flowers follow formation forms genera genus give given groups habits hand Hence hybrids important increase individuals inhabitants inherited insects instance instincts intermediate islands kind known land laws less living look males manner means modified namely natural selection naturalists nearly never objections observed occasionally occur organs origin parent perfect period plants points pollen present principle probably produced range remarked resemblance respect seeds seems seen separated shown side similar single slight sometimes species stage sterility structure successive supposed tend theory tion trees variability variations varieties various vary whole widely young