” I think the normal, healthy animal instincts in the human species are surprisingly weak.”
Gotta disagree there. The instinct to care for offspring is very strong in man compared to other species. Humans generally provide extraordinary care to their young. It is comprehensive and of long duration. It is necessary, of course, to support the rather long maturation of an animal whose brain takes up so much volume and energy.
Right you are on every point except, I think, in calling that "instinct" tout court.
More accurate to call that instinct as vastly strengthened and elaborated by culture.
Our brains, which take up so much volume and energy, also enable us to develop morals and manners, customs and cultures, which support and refine the good healthy mammal instincts. And occasionally even empower us, when appropriate, to override instinct for an intellectually-grasped greater good.
For intance, the phenomenon of a society organized to support individuals born with missing or shortened limbs or diabetes or facial deformities (like my adopted son who was born with a cleft lip and palate) is unknown in any other species. Very often, per instinct, they kill their defectives.
So we have cultures. We cultivate, channel, strengthen, and refine our appetites tendencies, and drives. And sometimes redirect them, for good or ill.