Which term describes a characteristic that can’t be controlled or learned?

The term that describes a characteristic that can't be controlled or learned is "instinct." Instincts are innate behaviors that organisms are born with, which means they do not have to be taught or developed through experience. These behaviors are often critical for survival and can include things like a bird building a nest or a newborn mammal's ability to suckle.

In contrast, the other terms listed—response, reaction, and behavior—often pertain to learned or controlled actions. A response is typically a reaction to a stimulus that may involve learned behavior, while a reaction is an immediate and sometimes conscious response to a specific event or stimulus. Behavior encompasses both learned actions and instinctual drives, and can include any range of activities or responses depending on the circumstances.

Thus, "instinct" stands out as the correct choice because it specifically refers to those traits and actions that are not learned and are inherent to an organism.