Star-Begotten by H.G. Wells

Dr. Holdman Stedding lay awake that night thinking about the state of mind of Mr. Davis and about the queer idea of a genetic invasion of Martian qualities that he had propounded. There was something provocative about the idea; something that made his intelligence bristle defensively. 'Pure balderdash!' he said aloud, but as a matter of fact what made it so irritating was that it was not pure balderdash. There was an attenuated but not unbreakable thread of silly plausibility about the suggestion that prevented him from throwing it altogether out of his mind. He threw words like 'balderdash' at it as one might throw stones at a dog that persists in following one, and presently there was the damned thing back again.

'If it should chance that something of the sort was going on.'