Sentence:  Living organisms had existed on earth, without ever knowing why, for over three thousand million years before the truth finally dawned on one of them. His name was Charles Darwin. To be fair, others had had <WSD>inklings</WSD> of the truth, but it was Darwin who first put together a coherent and tenable account of why we exist. 
Meaning of the word marked with <WSD> tags:  A slight knowledge or suspicion; hint.