Nature Vs. Nurture

Nature = biology - your genetic make up - determines the range of

an individual’s potential Nurture = socialization - everything that influences a

person since conception - determines the ways that

our human potential is actualized

Genes -  few single genes are responsible for any

one personality trait * inheritance is complex and

indirect - environmental influences can determine

whether or not a genetic trait develops or the strength of the trait

-  environments can trigger genes to influence an individual to engage in certain experiences

example: addiction to alcohol – a person must be exposed to alcohol in order to find out if they are genetically disposed to addiction

Therefore, both nature and nurture play roles in the development of a trait in an individual

example: height is an inheritable trait (genetic), but if diet is poor, then environmental influences affect height

Genes and Behaviour -  Thinking of ourselves as genetically

pre-programmed changes how we see ourselves as human beings

-  If we blame genetics for a particular behaviour, then does carrying the gene cause a self-fulfilling prophecy for the way a person behaves?

Study of Criminals In 1965, a study conducted in

Scotland found that 4% of all male inmates in Scottish prisons carried two copies of the Y chromosome (rather than one).

- in the general population, only 1 in a

1000 people carry the double Y chromosome

Media exploited the data claiming a biological basis for violence had been discovered.

•  The extra Y chromosome is linked to

low cognitive functioning

•  Is there another explanation that would explain the predominance of the double Y chromosome in inmates?

Criminals carrying the double Y chromosome are more susceptible to being caught because of the link between the double Y chromosome and low intelligence.

Therefore, the link is NOT between

the double Y chromosome and violence.

Biological Basis for Behaviour 1. Behaviour is often species specific - some behaviours are used by biologists to differentiate between species 2. Behaviours often breed true

- we can reproduce behaviours in successive generations of organizms ie: instinctive retrieval of a Labrador retriever

3.  Behaviours change in response to changes in biological structures

- brain injury can change personality - drugs can modify behaviour by

altering chemistry 4. Some behaviours run in families ie: bipolar, schizophrenia

5.  Behaviour has an evolutionary history that persists across related species - humans share 98% of their DNA

with chimps - we share behaviours that are

characteristic of highly social primates: nurturing cooperation facial expression

How do we determine if a behaviour is caused by nature or nurture?

Twin Studies Studying identical twins, reared

apart, gives clues as to what traits are possibly genetic and what traits are environmental

*If environment were the major

influence in personality, then identical twins raised in the same home would be expected to show more similarity than would the twins reared apart

http://www.youtube.com/watch?v=1gwnzW4jOMI

Minnesota Twin Study – 2009 Body Fat Identical twins -reared together 75% -reared apart 61%

Optimism and Pessimism – both influenced by genetics

Optimism - more environmental

Pessimism - largely controlled by genes

Religiosity (religious conviction and church attendance)

- strong genetic influence

Conscientiousness -  strong genetic influence

Agreeableness - environmental

Divorce -  If one identical twin is divorced, the

other is 45% of the time

-  If one fraternal twin is divorced, the other is, 30% of the time

In fact, the Minnesota twin study led the researcher to conclude: "[On] multiple measures of personality and temperament, occupational and leisure-time interests and social attitudes, [identical] twins reared apart are about as similar as [identical] twins reared together."

Interestingly, adoption studies have also shown the strong influence of genes (or nature). For instance, the Texas Adoption Project found "little similarity between adopted children and their siblings and greater similarity between adopted children and their biological parents."

Researchers at the University of Southern California found that when it comes to taking that first smoke, women are more likely than men to be affected by environmental factors such as peer pressure. Genetic factors, however, play a larger role in influencing men to start smoking.

Mayo Clinic researchers found that environmental factors, such as exposure to pesticides and industrial chemicals, play a greater role in men developing Parkinson’s disease, while genetic factors affect Parkinson’s susceptibility in women.

Identical Twins – Case Study Identical twins, Jim Lewis and Jim Springer

were only four weeks old when they were separated from their birth mother. Each infant was taken in by a different adoptive family. At age five, Lewis learned that he had a twin, but he said that the notion never truly soaked in until he was 38 years old. Springer learned of his twin sibling at age eight, but both he and his adoptive parents believed the sibling had died. The two men were finally reunited at age 39. the similarities the twins shared not only amazed one another, but researchers as well.

-  both men were 6’ tall -  both men were 180 lbs. -  both suffered from migraine

headaches -  both were named ‘Jim’

…easy to explain, right?

… but how do you explain the following? -  as youngsters, each Jim had a dog he

named, ‘Toy’ -  each Jim had been married two times - first wives were both named Linda

- second wives were both named Betty -  one Jim named his son, James Allan -  the other named his son, James Alan

-  each twin owned a light blue Chevrolet

-  each twin had driven their Chevrolet to Pas Grille beach, Florida

-  both Jims smoked Salem cigarettes -  both Jims drank Miller Light -  both Jims had had part time jobs as

sheriffs -  both were finger nail biters -  both liked leaving love notes to his

wife throughout the house