The phrase "baser instincts" refers to our primal or more animal-like instincts and desires. It often implies basic needs or desires that are considered less civilized or morally acceptable. Full definition
The resulting game of cat and mouse leads Tadek down an increasingly obsessive path which, unsurprisingly, exposes some of his own baser instincts in the process. (latimes.com)
We also know that the authorities can not watch everything we do, so it became necessary to invent all - seeing authorities that could manage people's baser instincts when nobody was looking. (religion.blogs.cnn.com)
The casual manner in which Nazis kill Jews, the semi-documentary tone, the horrors and ironies of the war itself and the gradual manner in which the audience comes to see Schindler as a man whose baser instincts slowly give way to compassion. (deseretnews.com)