Marlow is an English place name meaning "land remaining after the draining of a pond," so thoroughly practical in origin that it becomes almost charming as a name for a living creature. The literary association matters more: Charles Marlow, narrator of Conrad's Heart of Darkness, gives the name a quiet, watchful, morally serious quality.
The Literary Register
Conrad's Marlow is a reflective figure who witnesses difficult things and tries to make sense of them through storytelling. That narrative quality transfers to pets with an observant temperament: dogs who watch the room carefully, who track the household's mood. Border Collies and Aussies are obvious candidates.
Gender Neutrality and Human Crossover
The registry marks Marlow gender-neutral, tracking its emergence in baby naming for both boys and girls. See Marlow on the human side. That crossover quality follows the same logic that made Scout a popular neutral.
The Counter-Reading: Requires a Certain Dog
Marlow is a thoughtful name for a thoughtful dog. On a loud, excitable, uncomplicated personality, it sits awkwardly. The name makes a quiet promise about the dog's character that the dog then needs to keep, at least occasionally.