Chapitre 12: Motivation
I. The Hungry Animal: Motives to Eat.
A. The Biology of Weight.
Psychologist use to think that being overweight = sign of emotional disturbance. Later research
showed that overweight people aren’t more/less emotionally disturbed than slim people. Also found that
heaviness is not always a result of overeating. Many heavy people eat in large quantity, but so do
skinny people -> in a study where people ate a lot, skinny people had a hard time gaining weight as it is
for most heavy people to lose weight.
1. Genetic Influences on Weight and Body Shape.
Explanat*: biological mechanism keeps your body weight at a genetically influenced set point
(the weight you stay at when you’re not trying to gain or lose) -> can vary about 10% in each direct*. If
you go too high/low, your body will produce the need to eat/reduce eating to go back to the set point.
Everyone has a genetically programmed basal metabolism rate (the rate at which the body burns
calories for energy) and a fixed number of fat cell (stores fat for energy and can change in size). Obese
people have 2 the number of fat cells as normal-weight adults, and their fat cells are bigger. Fat cells
can’t disappear, when you lose weight they only get smaller.
A complex interact* of metabolism/fat cells/hormones keeps people at the weight their bodies
are designed to be. When a heavy person diets, their metabolism slows down to conserve energy and
fat reserves. When a thin person overeats, metabolism speeds up, burning energy.
Set-point theory predicts that the heritability of weight and body fat should be high, and indeed it
is: In twin and adopt* studies, heritability estimates fall between 0.40/0.70. Identical twin who were raise
apart have the same body weight and shape as twins raise together -> when they gain weight, it’s at the
same place. Genes also determines how much brown fat (energy-burning type of fat that seems
important in regulating body weight and blood sugar) a person had in addit* to usual white fat. It is
lacking in obese people, which may be one reason that fat people can’t burn all the calories they
A team of researchers isolated a genetic variation of the gene that causes mouse to become
obese. The usual form of the gene, obese/ob, causes fat cells to secrete a protein -> leptin (travels
through the blood to the brain’s hypothalamus, which is involved in the regulation of appetite). When
leptin is normal, people eat just enough to maintain their weight. When leptin is low, the hypothalamus
thinks the body lacks fat reserve and signals the individual to overeat.
Studies suggest that leptin plays is most role early in life, by altering the brain chemistry that
influences how much an animal/person eats. More specifically, leptin helps regulate body weight by
strengthening neural circuits in the hypothalamus that reduce appetite/by weakening circuits that
stimulate it. During a critical period in infancy, leptin influences the format* of those neural connect*, and
the set point is set. Some researches speculate that because of this early neural plasticity, overfeeding
infants while the hypothalamus is developing may later produce childhood obesity.
Researchers have identifies a number of other genes that are linked to being overweight. They
have discovered a gene that modulates product* of a protein that apparently converts excess calories
into heat rather than fat. Possess* of this gene may be one reason why slim people stay slim even
when they temporarily overeat.
Those findings as often raise the public’s hope for a breakthrough drug that will help people
lose weight easily and quickly. But taking leptin when overweight doesn’t produce much weight loss ->
leptin is only one of the influences on body weight, dozens of genes/body chemicals are involved in
appetite/metabolism rate/weight regulat*. Ex: receptors in nose/mouth that keep urging you to eat more,
receptors in your gut telling you to quit, and leptin/other chemicals telling you that you stored enough fat
Also, your brain will get high on sugary food even if your tongue can’t taste them/enjoy their
texture. Sweets increase pleasure-inducing dopamine levels in the brain, making you crave more rich
food. Some obese people may have underactive reward circuitry, which leads them to overeat to boost
their dopamine level. The complexity of the mechanism governing appetite and weight explains why appetite-
suppressing drugs inevitably fail in the long run: They target only one of the many factors that conspire
to keep you the weight you are.
2. The Overweight Debate
Increase in obesity has occurred in both sexes/all social classes/all group of age, in many
countries. More than ½ of all North American adults, and at least ¼ of all children/teenagers are now
overweight/obese. In 1994, obesity was estimated to directly cost Canadian taxpayers more than 1.8
billion in health care, approximately 2.4% of the budget was spent treating obesity/diseases directly
resulting from it. The reason is not genes, which cannot have changed so much in just a couple of
Health researchers are worried about this trend cause obesity is considered a leading risk
factor in diabetes, high blood pressure, heart disease, stroke, cancer… But what if a person is
predisposed to be fat but not obese? Lately some scientists have been cautioning the against the
emotional reasoning that “thin is in”. They believe that for some people the real problem is not
overweight but lack of fitness. Fat people that are physically fit are healthier and have lower risk of
illness, on average, than thin people who are sedentary. Because many overweight people have
sedentary habits, scientists have never thought to spate these 2 factors.
Jeffrey Friedman, primary discoverer of the gene for leptin, said that obesity epidemic is mainly
a result of the fact that fat people are getting fatter; thin people have remained pretty much the same.
Other scientists agree that genes plays a powerful role, but they observe that changes in
environment/culture are the reason why so many people are putting on weight.
Another major influence on weight is exercise, which boost body metabolic rate. When obese
women are put on severely restricted diets, their metabolic rates drop sharply, as set-point theory would
predict. But when they combine the diet with moderate physical activity, they lose weight and their
metabolic rate rise almost to the previous level.
B. Environmental Influences on Weight
1. The increase abundance of fast food and processed foods that is inexpensive, available,
and high in sugar. Human beings are genetically predisposed to gain weight when rich food is abundant
because, in our species evolutionary past, starvation was all often a real possibility. A tendency to store
calories in the form of fat provided a definite survival advantage. Unfortunately, evolution didn’t produce
a comparable mechanism to prevent people from gaining weight when food is easily available.
2. The widespread consumption of high-sugar, high-calories soft drinks. Throughout
human history, the proportion of calories consumes in beverage was really low, and thus the human
body did not evolve a mechanism that would compensate for fluid intake by lowering food intake.
3. The sharp decline in exercise and other expenditures of energy because of remote
controls, a preference for sedentary activity, and the speed and convenience of driving rather than
4. The increased portion sizes of food and drink. Servings of food/drink have become
supersized, double/triple what they were only one generat* ago. Even babies/toddler are being fed as
much as 30% more calories they need.
5. The abundance of highly varied food. When diets are predictable and routine, people
habituate to what they are eating and eat less of it.
C. The Body as Battleground: Eating Disorders
Evolut* has designed woman to store fat which is necessary for the onset of menstruat*,
healthy childbearing, nursing, and, after menopause, the product* and storage of estrogen. In cultures
that think women should be very thin, therefore, many women become obsessed with weight and are
continually dieting, forever fighting their bodies need for a little healthy roundness.
Some people lose that battle, developing serious eating disorders that reflect irrational terror of
being fat. In bulimia (eating disorder characterize by episodes of excessive eating, bingeing, followed
by force of vomiting or use of laxative, purging). In anorexia (eating disorder characterized by fear of
being fat, a distorted body image, radically reduced consumption of food and emaciation). Many people recover, but others damage their health permanently, or, in the case of anorexia, die of heart, kidney
failure or complications of osteoporosis. Their weakened bones simply collapse.
Those two are the most well-known eating disorders and occur most often among young white
women. But more than 40% of all cases of eating disorders occur among men, ethnic minority groups,
young children, and athletes, and do not fit criteria of anorexia/bulimia.
Genes may play a role in dvlp of eating disorders, particularly anorexia nervosa, which has
been found across cultures and throughout history, but so do psychological factors, including depress*
and anxiety, low self-esteem, perfectionism, a distorted body image, drug use and perceived pressure
from peers to lose weight. American culture is rife with “bodysnarking”, the relentlessly critical and snide
appraisals of other people’s bodies that get posted on blogs… and are constant topics for entertainment
magazines and talk shows.
Eating disorders and body-image distortions among boys/men are increasing too, thought they
take different forms. Just as anorexic women see their gaunt bodies as being too fat, some men have
the delusion that their muscular bodies are too puny. So they abuse steroids and exercise or pump iron
II. The Social Animal: Motives for Love.
A. The Biology of Love
Psychologists who study love distinguish passionate love (“romantic”), from companionate
love (affection and trust). Although the experience of romantic love is universal, many cultures have not
regarded it as the proper basis for anything serious, such as marriage.
Researchers try to explain passionate love by looking at the brain. There are olfactory cues in a
potential partner’s scent that can turn you on/off. There are physical cues in the potential partner’s voice
and body shape, and even in how similar his/her face is to you. There is the dopamine jolt of reward,
from the same dopamine that makes anticipation of a fabulous meal or an addictive drug so
pleasurable, and there are the arousal and excitement provided by adrenaline. And then there are key
hormones that turn that first phase of exhilaration into the longer-lasting phase of attachment and
Many biologically oriented researchers believe that the neurological origins of passionate love
being in infancy, in the baby’s attachment to the mother. In this view, maternal and romantic love share
a common evolutionary purpose, preserving the species, and so they share common neural
mechanisms, the one that make attachment and pair-bonding feel good. In fact, certain key
neurotransmitters and hormones that are involved in pleasure and reward are activated in the mother-
baby pair-bond and again later in the pair-bond of adult lovers and even of passionate friends.
The hormone oxytocin plays a crucial role in the attachment-caregiving system, influencing
feelings and expressions of love, caring, and trust not only between mothers and babies but also
Studies of animals also find that the characteristic feelings and actions that occur during
attachment are mediated by reward circuits in the brain and involve the release of endorphins
(chemical substances in the nervous system that are similar in structure and action to opiates). Findings
suggest that endorphin-stimulated euphoria may be a child’s initial move for seeking affection and
cuddling, that, in effect, a child attached to a parent is a child addicted to love. The addictive quality of
adult passionate love, including physical and emotional distress that lovers feel when they are apart,
may involve the same biochemistry.
Using fMRI, neuroscientists have founbd other neurological similarities between infant-mother
love and adult romantic love. Two researhcers have found that certain parts of the brain light up when
people look at images of their sweethearts, in contrast to other parts that are activated when they see
pictures of friends/furniture. And these are the same areas that are activated when mothers see images
of their own children as opposed to pictures of other children.
Clearly, the bonds of attachment are biologically based. But human love affairs involve many
other factors that affect whom we choose, how we get along, and whether we stay with a partner over
B. The Psychology of Love Evolut* has made it possible to form deep and lasting attachments without travelling the world.
In fact, the first major predicator of whom we love is plain proximity: the proximity effect (the people
who are nearest to you geographically are most likely to be the dearest to you, too). The similarity
effect (similarity in looks, attitudes, beliefs, values, personality and interest is attractive to human
beings). Although it is a commonly believed that opposites attract, the fact is that we tend to choose
friends and loves ones who are most like us.
1. The Attachment Theory of Love
Adults, just like babies, can be secure, anxious or avoidant in their attachments.
Securely attached: Rarely jealous or worried about being abandoned, more compassionate and
helpful and are quicker to understand and forgive their partners.
Anxious lovers: Always agitated about their relationships, they want to be close but worry their
partner’s going to leave them.
Avoidant people: Distrust and avoid intimate attachments.
According to the attachment theory of love, people’s attachment styles as adults derive in
large part from how their parents cared for them. If a child’s parents were cold and rejecting and
provided little or no emotional and physical comfort, the child learns to expect other relationships to be
the same. If children from secure attachments to trusted parents, they become more trusting of others,
expecting to form other secure attachments with friends and lovers in adulthood.
The avoidant style is particularly resistant to change, because people who are busy avoiding
one another never learn to trust someone long enough to become securely attached. However, even
avoidant or anxiously attached people can have successful, stable relationships if they find securely
attached partners who will put up with their insecurities. Although those who display an avoidant style
are not necessarily pathological, this style is commonly reported by people who also display
But a person’s own temperament could also account for the consistency of attachment styles
from childhood to adulthood.
C. Gender, Culture and Love
Neither sex loves more than the other one in terms of love at first sight, passionate love or
companionate love. Men and women are equally likely to suffer the heart-crushing torments and
unrequited love. They are equally likely to be securely or insecurely attached.
However, they differ, on average, in how they express love. Males in many cultures learn early
that revelations of emotion can be construed as evidence of vulnerability. Which are considered
unmasculine -> men than develop ways of revealing love that differ from the ways women do. Ex:
Western society, many women express feelings of love in words, whereas men express these feelings
in actions. Similarly, many women tend to define intimacy as shared revelations of feelings, but many
men define intimacy as just hanging out together.
These gender differences in ways of expression the universal motives of love and intimacy
reflect social, economic and cultural forces.
III. The Erotic Animal: Motives for Sex
It is true that for most special, sexual behavior is genetically programmed. But as observed in
human beings “sex is not a natural act”. For one thing, the activities that one culture considers normal
are often considered unnatural in another culture or historical time. Second, people have to learn from
experience/culture what they are supposed to do with their sexual desires and how they are expected to
behave. Third, people’s motivation for sexual activity is by no means always and only for intrinsic
reasons. Human sexuality is influenced by a blend of biological, psychological and cultural factors.
A. The Biology of Desire
1. Hormones and Sexual Responses One biological factor that seems to promote sexual desire in both sexes is the hormone
testosterone, and androgen that both sexes produce. This fact has created a market for the legal and
illegal use of androgens. The assumption is that if the goal is to reduce sexual desire testosterone
should be lowered and vice-versa. Yet these efforts often fail to produce the expected results. One
reason is that the symptoms of androgen deficiency are also those of depression and marital problems