In the introduction to The Origin of Species, he stated, “I am well aware that scarcely a single point is discussed in this volume on which facts cannot be adduced, often apparently leading to conclusions directly opposite to those at which I arrived.”
Katika utangulizi wa asili ya chimbuko la spishi, alisema, "Mimi nafaamu vyema kwamba hatua moja imejadiliwa katika kitabu hiki ambao ukweli hauwezi tolewa, mara nyingi unaonekana kuelekeza kwa hitimisho moja kwa moja kinyume na ule ambao nilifikia."