INTRODUCTION TO PSYCHOLOGY - Bilkent University



INTRODUCTION TO PSYCHOLOGY

Chapter 2

Evolution and the Biological Roots of Behavior

At the end of this Chapter you should be able to:

Learn about evolutinary roots of motivated behavior

Understand the achievement of Homeostatis

Learn about Eating

Learn about Threat and Agression

Learn about Mating

Charles Darwin

Rattled the world with his theory of natural selection

Wrote “Origin of Species”

Natural Selection

The Origin of Species

Finches developed gene mutation

Advantage over peers

More successful reproduction

Evolve to look different than species in different environments

How are these characteristics passed on?

How and why do traits evolve over time?

Gregor Mendel (1822-1884)

Studied pea plants

How characteristics change over generations

Set the framework for what we know today.

What do we know today about how characteristics are passed through generations?

Chromosomes

Structures in the nucleus of each cell that contain genes

Hold 1,000 or more genetic commands

Genes

Complex molecules

Provide basic blueprints as organisms mature from a fertilized cell.

DNA (deoxyribonucleic acid)

The complex molecule that is the constituent of genes

Controls production of proteins and enzymes that make up the body

Chromosomes

Come in pairs; from Mom and Dad

Corresponding gene pair

Dominant-exerts effect regardless of correponding gene

Recessive-exerts effect only if corresponding gene matches

Do not directly influence how we look, etc.

Controls enzyme and protein production

Enzymes and proteins influence our overall make up

Genotype –genetic blueprint determined by chromosomes

Phenotype –organism’sactual characteristics

Human Behavior

Homeostasis

Eating

Threat and Aggression

Mating

Homeostasis

Another area where biological perspective is helpful in understanding behavior:

Examining the mechanisms of HOMEOSTASIS and how they affect our behavior

Every organism has both an external and an internal environment.

Homeostasis: maintenance of the internal environment of the organism (concentrations of various salts in the body’s fluids, the dissolved oxygen levels, the quantities of nutrients like glucose etc)

Outside environment may fluctuate, but internal environment remains stable

Homeostasis involves many mechanism; including those that rely on “negative feedback”.

Ex: Home heating systems: A thermostata turns on the heater when the house’s temperature falls below a given setting. The heater than causes the house’s temperature to rise, and this rise serves as a negative feedback for the thermostat. When the house reaches the present temperature, the thermostat turns the heater off.

The Nervous System

All mammals (and all birds) are endotherms; organisms that maintain stable body heat.

Endothermic animals sometimes become too warm ; and so need to lose heat and sometimes too cold and so preserve the heat created by their own metabolic activity

These two activities are controlled by the autonomic nervous system

Autonomic Nervous System

Central Nervous System (CNS)

The brain and spinal cord

Peripheric Nervous System (PNS)

System of nerves outside of the brain and spinal cord

Send control to the glands and smooth muscles

Controls internal organs, usually not under voluntary control

The peripheral nervous system is subdivided into two:

sensory-somatic nervous system and the

autonomic nervous system

Autonomic Nervous System

Governed by the hypothalamus

Two branches

Sympathetic

Parasympathetic

[pic]

Sympathetic Nervous System

Triggered when body temperature is too low

Revives up body activity to prepare for rigorous activity

Increased heart rate

Slowing down of peristalsis (rhythmic contractions of intestines), so not using energy during digestion

Vasoconstriction

Contraction of skins capillaries

Parasympathetic Nervous System

Triggered when body’s temperature is too high

Restored body’s internal activities

Cardio slowing

Speeds up peristalsis

Vasolidation

Widening of skin’s capillaries

Stimulus

Body prepares for response

Body returns to normal

Human Behavior

Eating

Built-in system for regulating food intake

Maintain genetically determined set points; a weight the body tries to maintain (the target)

Liver

Hypothalamus

Stomach and Duodenum

Adipose Tissue

Maintains constant level of glucose in bloodstream

Liver

Too much glucose detected…

Glucose turns into glycogen and fatty acids

Liver signals to stop eating

Not enough glucose detected…

Stored glycogen and fatty acids turn back into glucose

Liver signals to eat

Hypothalamus

Contains glucoreceptors

Also sensitive to glucose levels in the blood

Sends signals similar to that of the liver

Stomach and Duodenum

Contains receptors sensitive to nutrients dissolved in digestive juices

Stops signaling hunger when proper nutrients are on the way

Adipose Tissue

Stores fat in cells to be used when glycogen runs out

Secretes leptin when cells are full

Chemical that indicates when no more fat storage is needed

Inhibits appetite stimulants

Such as neuropeptide Y (NPY)

Why so many signals?

Safety provided by backup systems

If one system fails, the organism is still protected

Different signals monitor different aspects of our nutritional needs

Leptin-longer term needs

Others (cues from stomach)-hour-by-hour energy requirement variations

Aside from our internal structures, what else can influence what and when we eat?

Immediate outside influences

Culture

Social

Cognitive

Obesity

Obesity is an eating disorder. We need to consider multiple factors if we want to understand eating behavior.

Is it because we eat too much?

Some people are predisposed to obesity due to their individual genetic pattern (i.e., set points).

Threat and Aggression

What happens biologically when we feel threathened? Self-protection

Internal adjustments necessary to respond to threat in environment

When threat detected: Sympathetic branch of ANS activated

Prepares body for immediate, intense activity. Surge of adrenaline released

Male aggression and hormones:

The male is the far more aggressive sex. This gender difference holds only for physical aggression. Testosterone (the male sex hormone) is associated with physical aggressiveness in many species.

Male versus female aggression:

Males use physical aggression (pushing and punching). Females use social aggression (spreading gossip and rumors, isolating unwanted friends).

Learning to be aggressive?

1. Explicit learning: someone demands or teaches us

2. Implicit: we observe

3. Seems to be causal; when we observe violence, we become violent

Is aggression inevitable?

Cultural values, testosterone, defending your territory, revenge etc...

If your opponent is stronger than you are, then you better not start the battle at all! This is a limit on aggression. Dominance hierarchy: who is the strongest in the group? Assigned status is a limit on aggression.

Nature-Nurture Debate

Relative importance of an individual's innate qualities (“nature”) versus personal experiences (“nurture”) in determining individual differences in behavioral traits.

Mating

Appearance

Matching

Gender Differences

Appearance

Humans value attractiveness in a partner

Who is attractive?

Isn’t beauty the eye of the beholder?

Facial Appereance

Cross-culturally

Shiny hair

No visible deformities

Clear skin

Symmetrical face

Average face (slight deviation can help)

Developmentally

Infants

Infants as young as 3-months-old look longer at adult-rated attractive faces

12-month-olds interact more positively with adult wearing “attractive” mask.

Why is there a preference for attractiveness?

Indication of health

Body Appearance

Women

Not size

Waist-to-hip ration

Mature pelvis adequate fat supply

Fertility and readiness for pregnancy

Not a strong relationship between facial attractiveness and health

The Matching Hypothesis

There is a strong correlation between the level of attractiveness of two partners

Prefer partners similar to themselves

The Matching Hypothesis

Attractiveness

Personality

Race

Ethnic origin

Social status

Education level

Family background

Income

Religion

Habits

Gender differences in mate selection / Animals

Females

Decide when to mate and mating partner

Most physical investment in breeding

Males

Advertise sexual availability

Gender differences in mate selection / Humans

Man seeking woman…

Physical attractiveness

Healthy and fertile

Youth

More reproductive years

Kindness

Intelligence

Less value of commitment

More jealous by sexual disloyalty

Women seeking men…

Older

Social and financial status

Better ensures offspring’s survival

Kindness

Intelligence

More value of commitment

More jealous of emotional disloyalty

Contribution of Biological Perspective

Biological perspective: much to teach us about mechanisms, evolutionary influence on behaviors

No aspect fully explained by biological perspective

Focus thus far: large scale processes/mechanisms

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