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For me, the most amazing content of this chapter is the section for sexual orientation. Because it shows that the set orientation is determined not by childhood relationships with parents, nor does it relate to fear, hatred, being molested or sexually victimized. It is actually determined by our gene, and the sex hormone surrounding the embryo during the prenatal period.

Basic Motivational Concepts

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In this section, we will introduce several fundamental motivational theories, the instinct theory, the drive-reduction theory, and Maslow’s hierarchy of needs.

Instinct Theory

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Instinct theory states that the genes predispose the species-typical behavior, thus, many complex behaviors have a fixed pattern throughout a species and are unlearned. However, instinct theory failed to explain many complex motives of humans.

Drive-reduction Theory

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Drive-reduction theory is a replacement of instinct theory. It states that the physiological needs create an arousal state which drives us to reduce the need. In addition to the needs, there are also incentives, the positive or negative environmental stimuli, which lure or repel us. Such a process can maintain homeostasis. It can be represented as follows.

Physiological need (food) \& Incentives (aroma of food) $\longrightarrow$ Drive (hunger) $\longrightarrow$ Drive-reducing behaviors (eating)

However, we are not simply walking homeostatic systems but something more. When we are well-fed, we tend to do something more interesting, so are many animals. The motives that emerged after the satisfaction of basic needs can increase arousal, which is actually breaking the homeostasis.

Why you want to climb Mount Everest? -“Because it is there.”

A new term – optimum arousal – has to be involved in addition to homeostasis. We can therefore state that motivations aim not to eliminate arousal, but to somehow maintain it to an optimum level. When we are well-fed, we may go outside to explore the mall. Here, we have eating and shopping. Eating eliminates the arousal coming from homeostasis, whereas shopping increases the arousal again to some optimum level, making us not so bored. Bear this in mind, we have an interesting law.

Performance increases with arousal only up to a point, beyond which performance drops. - Yerkes-Dodson law.

According to this law, the arousal required is task-specific. A difficult task tends to require lower arousal. When we are taking an exam (a mild difficult task), it is good to be * focused, but not that *nervous. When we are driving on the high road (easy task), it is good to stay alert, instead of being sleepy.

Drive-reduction theory cannot explain the various priorities of needs. We need air, food, and water, we also desire to achieve personal success and establish a deep connection with others. Maslow’s hierarchy of needs can address this problem.

Maslow’s Hierarchy of Needs

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Maslow describes the priorities as a pyramid. At the base locates the physiological needs, only if which is satisfied can we move to the next level of needs, to love, achieve, etc. Some motives are more compelling than others. The pyramid is described as follows.

Physiological needs $\longrightarrow$ Safety needs (controllable and predicable) $\longrightarrow$ Belongingness and love (companion and acceptance) $\longrightarrow$ Esteem needs (achievement, independence, and recognition) $\longrightarrow$ Self-actualization needs (Accomplishment of the fullest and unique potential) $\longrightarrow$ Self-transcendence needs (meaning and identity beyond self)

When I started my Ph.D. life in NTU, though my physiological needs could be satisfied (by unfamiliar tastes), I felt not so safe, because it was hard to understand others’ speakings, let alone the coursework and group meeting. Two years later, after I got acquainted with *South-east Asian English, teaching assistant tasks, and noob-level deep-learning understanding, the safety needs were finally satisfied to some extent. Nowadays, I can finally proceed to the needs of belongingness, love, and esteem, to network, to achieve, to plan the future, and also seek to know myself.*


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In this section, we shall discuss the physiology and psychology of hunger, followed by an interesting topic about weight control.

Nobody wants to kiss when they are hungry.

The homeostatic system of ours is designed to maintain normal body weight and adequate nutrient supply, thus, we hunger and feed. So what exactly happens in our body when we are hunger?

Such an event involves multiple organs like the stomach, intestines, liver, and brain, all starting with the drops of blood glucose level. Without being consciously known, our brain, or specifically, the hypothalamus, which is the neural traffic intersection, monitors the blood chemistry and our body’s internal state, and trigger hunger. Once fed, other cerebral areas and hormones for appetite-suppressing function so that we feel sated.

In addition to physiology, there is more to hunger than meets the stomach. The memory of the last meal let us anticipate the next meal on time and feel hungry. And we also tend to favor sweet and salty tastes because they are genetically encoded.

Weight Control

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(Here we do not consider the genetic factor and long-term changes on food consumption and activity level.)

Three terms are directly related to weight control: food intake, energy output, and basal metabolic rate. The latter refers to the rate of energy expenditure for maintaining basic body functions when at rest.

A fourth term set point comes to combine the three. The set point defines our body weight, so that when our weight falls below it, hunger increases and metabolic rate decreases, in order to restore the lost weight.

Now we can explain why is it so difficult to lose weight. Fat has a lower metabolic rate than muscle does. As a result, an over-weight person has a lower basal metabolic rate, and requires less food to maintain the weight. (This means that once the person overeats, it’s easier to attain weight.) Once an over-weight person’s body drops below its set point, the brain will trigger increased hunger and decreased metabolism. And the body will burn off fewer calories (tend to sit still longer) and seek to restore lost weight. Such a process may easily lead to excessive energy intake.

Let’s try another question, why two people of the same height, age, and activity level can maintain the same weight, even if one of them eats much less than does the other? Recall the three terms we aforementioned. Here, the energy output is the same, and the food intake is quite different. Therefore, to maintain the same weight, the basal metabolic rate should also be different. The one eating less has lower basal metabolic, his/her body burns off fewer calories. The one eating more has a higher basal metabolic, his/her body burns off more calories. Though they have the same activity level.

Here comes the tips for weight control.

  • Take exercise.
  • Get enough sleep.
  • Minimize food-related incentives.
  • Limit food variety.
  • Eat healthy foods.
  • Use smaller bowls.
  • Eat less, eat slow, and eat regularly.
  • Decide how much to eat before attending a meal.
  • Be persistent even if lapsed occasionally.


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Sex is a part of life.

Sex is not like hunger. Without it, we may feel like dying, but we will not.

Sexual motivation is influenced by sex hormones. During the prenatal period, they guide our development as males or females. During puberty, they usher us into adolescence. After which in our later adult years, they activate sexual behavior.

Testosterone is one of the most important sex hormones. The sexual interest of males and females may wane once the testosterone level drops. Sexual arousal can be both a cause and consequence of an increased testosterone level. Testosterone to humans is like fuel to cars, without which a car will not run. But if the fuel is minimally adequate, adding more fuel won’t change how the car runs.

Sexual Orientation

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How many people are exclusively homosexual? A study conducted in Europe and the United States report $3-4\%$ for men and $2\%$ for women. And about $5\%$ of Google pornography searches are for gay porn.

What is the feeling of being homosexual in a heterosexual culture? To answer, we may simply imagine the feelings that we are blamed and isolated because we openly admit or display our feelings towards someone of the other sex. Or, if all the media and ads portray or imply homosexuality. Or, if our families are persuading us to change our heterosexual lifestyle and to embrace homosexual marriage. We may at first attempt to ignore or deny our desires, hope that it will go away. But it doesn’t. Then we may resort to psychotherapy, willpower, or prayer. But the feeling is still there. Indeed, sexual orientation operates unconsciously, and is neither wilfully chosen nor wilfully changed.

What determines sexual orientation? Is it related to childhood relationships with parents? Does it involve fear or hatred of people of the other sex? Or is it related to being molested, seduced, or sexually victimized as children by an adult homosexual? No. Abundant researches find no evidence supports the claims.

Then, where do these preferences come from? There are at least three types of differences: brain differences, genetic differences, and prenatal influences.

For brain differences, compared to straight men, one of women’s and gay men’s hypothalamic cell clusters is smaller. Gay men’s hypothalamus reacts as the same as straight women’s do to the smell of sex-related hormones.

For genetic differences, shared sexual orientation is higher among identical twins than among fraternal twins. Sexual attraction in fruit flies can be genetically manipulated.

For prenatal influences, altered prenatal hormone exposure may lead to homosexuality in humans and other animals. Exposure to the hormone levels which ought-to-be-experienced by female fetuses can lead the person (regardless of the sex) to be attracted to males in later life. Thus, female fetuses most exposed to testosterone, and male fetuses least exposed to testosterone, tend to later exhibit most likely gender-atypical traits and same-sex desires.

Another prenatal influence comes from the mother’s immune system. Men who have older brothers are somewhat more likely to be gay. The homosexuality is roughly $2\%$, $\sim 3\%$, and $4\%$ for the first, second, and third sons, respectively, with an approximately one-third increase in percentage. The reason? Maybe the defensive maternal immune response to foreign substances produced by male fetuses. With each pregnancy with a male fetus, the mother’s maternal antibodies become stronger and may prevent the fetus’ brain from developing in a male-typical pattern.