Darwin's book 'On the Origin of Species by Means of Natural Selection' (henceforth The Origin) abounds with metaphors. In fact, the very theory of natural selection is couched in a system of metaphors that exhibit striking consistency and coherence. I argue that the phenomenon for which Darwin tries to detect the basic mechanisms, that is, biological evolution, involves vast, indeterminate, and ambiguous observations that are difficult to subject to the empirical methods. This fact motivates Darwin's extensive use of metaphors to organize his observations, structure the vague concepts, and ultimately render his observations meaningful and intelligible. I demonstrate that Darwin's metaphors, as far as they are elements of Idealized Cognitive Models, prove valuable in achieving this goal. First, I identify the conceptual metaphors underlying the main metaphorical expressions and show how these conceptual metaphors give rise to entailments and inferences central to Darwin's theory. The conceptual metaphors I identify are "NATURE IS A MOTHER," "NATURE IS A BREEDER," "LIFE IS WAR," "LIFE IS A RACE," and "EVOLUTION IS PROGRESS." I also comment briefly on the conceptual blending involved in these metaphorical mappings. I then turn to characterizing the idealized cognitive models (ICMs) that function as the pre-conceptual ground in virtue of which Darwin's metaphors are meaningful, coherent, and helpful to scientific thinking. These ICMs are the ICM of STRUGGLE and the image-schema of SOURCE-PATH-GOAL. (Abdulsalam Al-Zahrani)