1. Behavior Genetics

2. Predicting Differences
Why are you the unique way you are?
While you are unique, you are also very similar to others.
Develop language
Feel hunger
Major physical features
Feel drawn to produce & protect offspring
Looks
Sound
Personality
Interests
Cultural & family background

3. Predicting Differences
What causes our diversity, and our shared human nature?
How much is attributed to environment?
How much is attributed to our genes?
These are questions of behavior genetics:
The study of the relative power and limits of genetic and environmental influences on behavior.

4. Nature vs. Nurture Nature:
The influence of our DNA that directs the inherited traits that influence our
Nurture:
The influence of the environment on our personality, physical growth, intellectual growth, and social interactions.
personality, physical growth, intellectual growth, and social interactions.

5. Let’s look at nature influences
Nature vs. Nurture
Let’s look at nature influences

6. A Little About Genes 46 Chromosomes, 23 from each parent
Each chromosome is made of a coiled chain of DNA
Genes
segments of DNA located on chromosomes
transmit all heredity traits

7. A Little About Genes
Genetically speaking, every other human being is your twin.
Your DNA is 99.9% the same as the person sitting next to you.
Humans and chimpanzees share about 96% of our DNA sequence.
How much difference does that 4% make?

8. A Little About Genes Most of our traits are influenced by many genes.
How tall you are
The size of your vertebrae, leg bones, etc.
Traits such as intelligence, happiness, aggressiveness are similarly influenced by groups of genes.

9. Adoption & Twin Studies
Identical Twins
Single egg that splits
Genetically identical
Don’t always have the same number of copies of those genes
Fraternal Twins
Separate eggs
Genetically similar, as ordinary brothers & sisters

10. Adoption & Twin Studies
Are identical twins behaviorally similar?
Studies on personality traits of extraversion & neurotic scales show they are more similar than fraternal twins
Social traits?
1500 same-sex, middle-ages twins divorce rates studied
When a fraternal twin divorced, other was 1.6 times more likely to divorce than twins who didn’t divorce.
Identical twin divorced resulted in other being 5.5 times more likely to divorce.
Differing divorce risk about 50% attributable to genetics.

11. Separated Twins
Twins separated at birth but raised in different homes have more traits of biological parents than adoptive parents.
Anecdotal stories of Identical twins separated at birth with amazing similarities.
The Jim Twins

12. Environmental Influence
Study by comparing biological relatives and environmental relatives
Personalities of biological relatives are as diverse as non-related people
While adopted children are more like their biological parents, most adopted children benefit greatly from the environment of their home.
Bottom line:
Environment affects genetic predisposition

13. Heritability Heredity and heritability are different.
Heredity is the percentage or proportion of a trait that is inherited.
Heritability is the proportion of variation among individuals that are attributed to their differing genes.
Heritability is the extent to which differences among people are attributed to genes.

14. Heritability
Mark Twain suggested raising boys in barrels until age 12, feeding through a knot-hole.
Boys would emerge with lower-than-average IQ scores because of their environment.
Because of the similar environment, test score differences would be attributed to heredity.
Heritability, the differences due to genes, would be near 100%

15. Heritability
As environments become more similar, heritability as a source of differences becomes more important.
If all people had very similar heredities, but were raised in different environments, heritability would be much lower.

16. Gene-Environment Interaction
Imagine two babies: one predisposed to be attractive, social & easy going, the other not so much.
First baby attracts more affectionate & stimulating care
Develops into a warmer and more outgoing person
Seeks activities & friends that further social confidence.

17. Gene-Environment Interaction
Certain types of environments trigger genetic expression.
Genes have the potential to influence development, environmental factors switch them on or off.

18. Gene-Environment Interaction
Genes are self-regulating
They react rather than lead the way.
Genes and the environment work together like two hands clapping. They interact.

19. Nature vs. Nurture is the wrong way to look at behavioral genetics
Nature vs. Nurture is the wrong way to look at behavioral genetics. Instead think of it as Nature via Nurture