Biological and Internal Theories of Motivation

Human behavior is motivated by biological drives such as hunger, thirst, and sexual desire and by psychological desires.

Motivation is the driving force behind actions and behaviors. Many different types of motivation inspire human behavior and goals. Basic biological drives, such as thirst and hunger, support the goal of survival. Another biological motive is sexual desire, which supports goals of pleasure and procreation.

According to the drive-reduction theory of motivation, imbalances in the body create a physical need and psychological motivation to return to balance. Homeostasis is the balanced or optimal level maintained within a biological system. In the biological system of the human body, the brain acts as the control center. It receives both neural (nerve-based) and hormonal messages from the rest of the body and uses that information to maintain balance. A behavioral response that returns the body to homeostasis is more likely to become a habit, or repeated behavior.

The arousal theory of motivation states individuals try to maintain an optimal level of arousal. In this context, arousal refers broadly to a state of mental or physical excitation. People will either approach or avoid certain people or situations to maintain this level. If someone has a low level of arousal, they feel bored and look for stimulation. If someone has a high level of arousal, they become anxious, overstimulated, and unfocused.

According to the Yerkes-Dodson law, developed in 1908 by psychologists Robert M. Yerkes and John Dillingham Dodson, the optimal level of arousal can change based on the task at hand. A high level of arousal boosts performance on simple tasks but impairs work on complex tasks.
In general, optimal task performance is reached when arousal levels are moderate. However, the Yerkes-Dodson law states that easy tasks are performed best at a higher level of arousal and difficult tasks are performed best at a lower level of arousal.
The regulatory focus theory states that human motivation is rooted in acquiring pleasure and avoiding pain. Pain and pleasure can involve more than basic physical states. Regulatory focus theory considers both promotion (achievement) and prevention (safety). For example, a person can improve his or her health either by exercising and eating healthy food (promotion) or by avoiding eating junk food (prevention).

Humans have evolved complex psychological motivations over time. The incentive theory of motivation suggests that people are motivated to act in order to acquire rewards (e.g., studying for an exam to earn a high grade). Intrinsic motivation (self-motivation) involves an internal drive to engage in behavior because one finds the behavior itself rewarding. Intrinsically motivated behaviors provide personal satisfaction, such as playing an instrument for pleasure. Canadian psychologist Albert Bandura identified self-efficacy, or a belief in one's ability to complete tasks successfully, as an important motivator. A higher level of confidence, or self-efficacy, makes people more likely to take on challenging tasks and see them through.

Self-determination theory states that internal and external factors work together to motivate an individual. Autonomy (acting of one's own volition), competence (self-efficacy), and relatedness (a sense of belonging or connection) are considered three basic psychological needs influencing individuals' motivation. When these needs are satisfied, people are more likely to be happy. Furthermore, people will be more motivated to engage in an activity when they feel they are doing so by their own choice, when they believe they are good at it, and when they can share the activity with others.

External Theories of Motivation

Once basic needs for food and safety have been met, social and environmental factors become important motivators.

People are often motivated by the desire for achievement or social connection. Extrinsic motivation is a drive to engage in a behavior to obtain an external reward or avoid an unwanted consequence. Extrinsically motivated behaviors are done with the hope of receiving some sort of benefit or recognition. Potential motivators include intimacy, popularity, public recognition, good grades, approval, money, and power.

In 1943 American psychologist Abraham Maslow introduced a hierarchy of needs ranking biological, internal, and external motivators. Maslow's hierarchy of needs is represented by a pyramid with the most important motivators as the base. The basic biological needs of food, water, and shelter take priority over more complex motivators. Next are needs for safety and security, followed by relationships and belonging. Maslow's hierarchy of needs also includes accomplishment, self-worth, and self-actualization. Self-actualization means reaching one's full potential. Maslow studied people he considered self-actualized, such as American author Helen Keller and Indian activist Mahatma Gandhi. He noted that they were creative, confident without being arrogant, and accepting of others. Self-actualized people do not depend on the approval of others, which makes them able to push back against social norms or unfair political structures.

Maslow's Hierarchy of Needs

Psychologist Abraham Maslow developed a hierarchy of needs. This hierarchy ranks basic physical survival needs as most important. It also recognizes the importance of higher social and emotional needs, which can be pursued once physical needs have been met.
In 1961 American psychologist David McClelland introduced the achievement theory of motivation. This theory states every person is motivated by one of three extrinsic motivators: achievement, affiliation, or power. These constructs are analogous to those in self-determination theory. Achievement is similar to competence, affiliation to relatedness, and power to autonomy. The theory also suggests these social motivators and need to belong are learned over time through culture and life experiences. Each motivator has a specific set of accompanying characteristics. The person motivated by achievement has a strong need to set and accomplish goals, likes to receive feedback on their progress, and prefers to work alone. The person motivated by affiliation wants to belong to a group, goes along with whatever the group decides, and favors collaboration and low-risk circumstances. The person motivated by power yearns for status and recognition, likes winning competitions, and wants to control and dominate others.


The human body has built-in mechanisms to regulate hunger, eating habits, and weight; however, social and environmental factors also have influence.

Eating is a primal instinct essential to the survival of humans and animals. Hunger motivates animals to seek food. Eating leads to satiation, or feelings of fullness and satisfaction.

Hunger is regulated by several systems. Empty stomach contractions cause hunger pangs and the release of chemical secretions. Low blood glucose levels causes the pancreas and liver to send chemical signals to the brain, triggering hunger. Eating causes blood glucose levels to rise. This leads the pancreas and liver to send signals to the brain to shut off hunger, and eating stops. Satiety signals are also sent to the brain when food passes through the gastrointestinal tract and when fat cells release leptin, a hormone that signals fullness. Within the brain, the lateral and ventromedial hypothalamus are responsible for regulating hunger.

Eating habits can influence body weight, but genes and the environment are also important factors. Calories are units of energy that are consumed and burned. If the number of calories eaten exceeds the number of calories burned, the excess energy is stored as fat. If the number of calories eaten is less than the number of calories burned, stored fat is used for energy. A person's energy expenditure is affected by their activity levels. However, their metabolic rate must also be considered. The metabolic rate is the rate at which an individual expends energy. People with a high metabolic rate, or a high metabolism, burn calories quickly and easily. People with a low metabolic rate, or a low metabolism, take greater effort to burn calories and burn them slowly.

Fluctuations in body weight are normal but usually occur within a narrow margin in the absence of extreme changes to diet or physical activity. A set point is a value where the physiological state of the body is stable, like a stable weight range for an individual, maintained by changes in metabolism. If changes in diet or exercise shift the body from this set point, metabolism will increase or decrease to restore balance. This resistance to change is one reason that people have difficulty maintaining weight loss. A person's set point is determined by their genes, which are inherited, and the environment.

Social, environmental, and socioeconomic factors also influence what and how much people eat. Portion sizes exceeding the suggested serving amounts became common in the late 20th and early 21st centuries, contributing to obesity worldwide. Inexpensive foods that are high in fat and sugar and low in nutritional value have also led to a global increase in obesity. For example, people living in urban areas or poorer neighborhoods may not have healthy food options at the grocery store. They must instead rely on readily available, inexpensive, and high-calorie fast food as their main source of nutrition. Because these foods have negligible nutritional value, larger portions are needed to feel full, as the body is starved for nutrients even after eating.

Obesity Rates in the United States

Over the last several decades, obesity has increased significantly in the United States. Almost 40 percent of adults are obese. Obesity can occur due to medical conditions, overeating, a lack of physical activity, or a combination of these factors.