Equal Opportunity Annoyance

The party line is that humping by dogs is a sign of dominance and is not related to sexual thoughts or connotations. I'm not so sure about that.

Regions of the brain that control both aggression and sexual behavior are so close that some overlap in executive function is inevitable. In intact males, testosterone activates both brain regions, enhancing aggressive responding, mounting (humping), wanderlust (roaming), and urine marking.

Neutering reduces or eliminates these behaviors in most but not all dogs. That is because these same brain regions were masculinized in utero so a neutered male is still a male (albeit with the "dimmer switch" turned down), not an "it." Neutered males may still exhibit aggression and some continue to hump. Drugs that reduce aggression (like Prozac) also attenuate sexual behaviors, an unwanted side effect in humans but not dogs. Estrogen is structurally almost identical to testosterone and can promote aggression in intact bitches when they are in heat. Aggression and humping may occur in intact and spayed bitches for similar reasons that they occur in males because both sexes are programmed to exhibit the same behaviors, though at different frequencies and intensities. I call this variable expression of sexually dimorphic behaviors the Lou Reed effect. 

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