On the surface, L'Humanite is about a detective, Pharaon, dealing with his hyper sensitive nature to a rape/murder of a young girl he is investigating, but especially for his unrequited love to his neighbor, Domino. Pharoan is like a wounded, or fearful child, dumpy, perpetually slumped over, soft spoken, watery eyed, whereas Domino is considerably working class, modern, damaged, but not nearly as fearful, at least, not as openly sensitive; unlike Pharaon, she doesn't wear her fear like bad suit. But, that is just the surface of the characters and story, the actual definition of these key elements is left up to the viewer. The plot and the characters are fragments. Instead of miring itself in details, long monologues, heavy dialogue in general, or normal cinematic conventions, the film is purposefully left incomplete in many areas. Thus, the viewer is left to speculate how these gaps should be filled, left to ponder the scraps given to them.
For example, we are told Pharaon's girlfriend and child left him, but not why. Is Pharaon's sensitivity a product of his being abandoned by this woman, or was his sensitivity the cause of her leaving? Domino is clearly upset when Pharaon mentions the case of the rape/murder of the young girl, but is her reaction just empathy, or something deeper? For every detail we are given, there are often unresolved questions that are never conveniently answered.
It somewhat reminds me of a Shohei Imamrua film, like Vengeance is Mine or The Eel, in that the story unfolds through rather mundane scenes, but these scenes end up speaking volumes over the course of the film. You could also say it is a bit like Antonioni as well, as the ordinary, often bright, landscape often contributes just as much emotion as the characters. Basically, Brumo Dumont, like Imamura or Antonioni, eschews normal narrative conventions to tell a story. He lets the viewer fill in the gaps, and much of the film will always remain an engaging mystery.