Evolutionary Evolutionary PsychologyPsychology

The study of evolutionary The study of evolutionary explanations for shared explanations for shared

human behaviors.human behaviors.

Topics in Evolutionary PsychologyTopics in Evolutionary Psychology

Why do humans tend to pair off Why do humans tend to pair off monogamously?monogamously?

Why do babies tend to develop Why do babies tend to develop stranger anxiety at about the same stranger anxiety at about the same age (8-13 mo.)?age (8-13 mo.)?

Why are people more likely to Why are people more likely to develop a phobia of spiders than of develop a phobia of spiders than of guns?guns?

Evolutionary psychologists use Evolutionary psychologists use natural selection to explain natural selection to explain

behaviors.behaviors. What is natural selection?What is natural selection?

– (1) Genetic differences between (1) Genetic differences between individuals in a species causes (2) some individuals in a species causes (2) some organisms to be better suited to their organisms to be better suited to their environment. (3)These organisms are environment. (3)These organisms are more likely to survive and pass on their more likely to survive and pass on their genes so (4)these traits become more genes so (4)these traits become more common in successive generations.common in successive generations.

Why does stranger anxiety appear Why does stranger anxiety appear between 8-13 mo?between 8-13 mo?

1.1. Genetic mutations create variation in Genetic mutations create variation in when stranger anxiety appears:when stranger anxiety appears:

1.1. 0 months0 months2.2. 3 months3 months3.3. 6 months6 months4.4. 9 months9 months5.5. 1 year1 year6.6. 2 years2 years7.7. 3 years3 years8.8. NeverNever(For simplicity, assume stranger anxiety persists (For simplicity, assume stranger anxiety persists

for 6-8 months from onset.)for 6-8 months from onset.)

Why does stranger anxiety appear Why does stranger anxiety appear between 8-13 mo?between 8-13 mo?

In what way are the infants that In what way are the infants that develop stranger anxiety at 9-12 develop stranger anxiety at 9-12 months better suited to their months better suited to their environment?environment?

0-6 months – what is the danger in 0-6 months – what is the danger in getting stranger anxiety too early?getting stranger anxiety too early?

2 years-never – what is the danger in 2 years-never – what is the danger in getting stranger anxiety too late?getting stranger anxiety too late?

Your turn:Your turn:

Develop an evolutionary hypothesis for Develop an evolutionary hypothesis for the following common human the following common human behavior:behavior:

Children protest going to bed.Children protest going to bed.

Evolutionary Psych DataEvolutionary Psych Data1. 5-year-old 1-year-old

2. 40-year-old 20-year-old

3. Older Younger

4. Good financial prospects An attractive body

Good-looking face Ambition and industriousness

Caring personality Exciting personality

5. a. Father Mother

b. Parents of father Parents of mother

c. Younger parents Older parents

6. a. Death of a son Death of a daughter

b. Death of an unhealthy child Death of a healthy child

Gender Differences in Gender Differences in ReproductionReproduction

Women

• Sure the baby is hers• Invests lots of time/energy

into each child• Can only make one baby

per 9 month period (usually)

Men

• Less sure the baby is his

• May invest very little time and energy into each child

•Have virtually unlimited reproductive potential

Therefore, it is in the woman’s best interest to be choosy about who she mates with, picking only men who are 1) likely to have good genes, and 2) willing and able to provide for her and the child.

How does a women know?How does a women know?

Good looks often indicates good genes.Good looks often indicates good genes.

- Masculinized physical features - Masculinized physical features correlates positively with better correlates positively with better immune function.immune function.

- Facial symmetry indicates lack of - Facial symmetry indicates lack of parasite infection.parasite infection.

How does a women know?How does a women know?

- Feminized facial features correlate - Feminized facial features correlate positively a greater willingness to positively a greater willingness to help raise children.help raise children.

-So do we look for masculine or feminine features?

-It depends.

Mate selection and the menstrual Mate selection and the menstrual cyclecycle

Menstrual Cycle Alters Face Preference

0

5

10

15

20

25

Low conceptionrisk

High conceptionrisk

% fe

min

izat

ion

pref

erre

d

Japanese Faces

Caucasian Faces

Darwin AwardDarwin Award

Honoring those who improve the Honoring those who improve the species...by species...by

accidentally removing themselves accidentally removing themselves from it!from it!