The biological category includes many different theories; I have included three that I find to motivate the most. These are instinct, arousal, and drive-reduction.
The instinct theory describes behavioral patterns that are unlearned, such as curiosity, fear, love, etc. Instincts vary from person to person, but we are all naturally drawn to behaviors that keep us safe as well as alive. We are motivated by evolution; programmed, as it were, to behave according to what survival deems necessary. As babies, we suckle in order to eat, and we get scared when something startles us. We also have many human instincts that determine our behavior. We blush when we feel embarrassed, bow our heads when we feel shame, and feel nauseous when we are repulsed. This helps us to survive and gives behavior a genetic component.
Drive or drive-reduction is when a state of tension is created (drive) and we are motivated to reduce it. This theory has a biological component because there are biological needs that have to be met. For example, when we are thirsty, we seek something to eliminate that thirst. We sleep because we are tired and we eat because we are hungry. The tension of these needs drive us to reduce that tension by fulfilling that need.
In this theory, we are motivated to achieve certain levels of arousal; too much or too little diminishes our performance. Biologically, we are compelled to engage in certain behaviors. For example, we want to be playful as children so we seek to maintain that arousal through behaviors of playfulness. If a child is able to play, then their arousal can be met, and that drive is being fulfilled. However, if that child does not get to play, that arousal will be unmet, making that child’s behavior reflect that unfilled arousal (cranky, crying, tantrums, etc.). If that child gets too much play, they will continue to stay at that state of arousal, wanting and needing to play all the time.
We behave in such a way to help satisfy, as well as, maintain optimal levels of arousal. We all have arousal needs but some people need more than others. Someone with high levels of arousal will seek behaviors that are more exciting (sky-diving, speed racing, rock-climbing, etc.) whereas people with lower levels of arousal will seek less exciting behaviors to stay optimal. We are also motivated to sustain optimal levels and will behave a certain way in order to do that. When we are bored, anxious, or antsy, we call a friend, go for a walk or do something else in order to bring arousal levels back up. The same goes for when arousal levels are too high. We seek to bring down those levels by finding ways to calm oneself by reading, watching TV, or adult coloring (love the new trend).