Genetics & Behavior

1. Genetics
& Nature vs. Nurture

2. Nature vs. Nurture Debate
Nature:
Our genetics
determine our
behavior. Our
personality traits and
abilities are in our
“nature.”
Nurture:
Our environment,
upbringing, and life
experiences determine
our behavior. We are
“nurtured” to behave
in certain ways.

3. Pair-Share
Do you think you share any personality traits
with your parents or grandparents?

4. Behavioral Genetics:
The study of the effects of heredity on behavior.
Behavioral genetics tries to answer this question:
To what extent are our abilities, personality traits, sexual
orientations, sociability, and psychological disorders
determined by genes inherited from our parents?
Will this
child be
more
like her
birth
parents
or
adoptive
parents?

5. Twin Types
Sperm
Egg
Identical twins have 98-99%
gene similarity because they
both develop from a single
sperm and single egg (which
splits into two fetuses).
Fraternal twins have 50% gene
similarity because they develop from
two different sperm and two eggs.
Fraternal twins have the same gene
similarity as regular siblings.

6. Twin Types
Identical twins have 98-99%
gene similarity because they
both develop from a single
sperm and single egg (which
splits into two fetuses).
Fraternal twins have 50% gene
similarity because they develop from
two different sperm and two eggs.
Fraternal twins have the same gene
similarity as regular siblings.
Fraternal twins from mixed race parents!Identical twins are always the same gender.

7. Heritability
Heritability is an estimate that indicates how
much of a trait can be attributed to genes.
If a trait is more similar in
identical twin than it is in
fraternal twins, we predict
that the trait has high
heritability.
If an adopted child has a
trait more similar to their
biological parent than to
their adoptive parent, we
predict the trait has high
heritability.

8. Heritability
If we can see many generations of trait similarity between
parents and their children, we predict that the trait has high
heritability.
If great-grandma, grandma, mom, and daughter all have addiction
problems, we can predict that addictive habits are heritable.

9. Twin Studies
Twin Studies are used to help us answer the question of “nature
vs. nurture.” Because identical twins share the same genetic
makeup, we can assume that differences between them
are due to environmental factors.

10. Twin Studies
Pair 1:
Same DNA
Same Environment
However, twins often grow up in
very similar environments.
If intelligence is the same, it’s
hard to tell if it is due to genetics
or environment.
Pair 2:
Same DNA
Same Environment
If intelligence is different, we
can assume that there are tiny
differences in environment (different
friends, time spent studying, etc.)
that caused the difference.

11. Twin Studies
Pair 4:
Different DNA
Same Environment
One sibling is adopted.
If intelligence is the same,
it is likely due to environment.
If intelligence is different, it is
likely due to genetics.
Pair 3:
Same DNA
Different Environment
Twins adopted by different
families grow up in different
environments.
If intelligence is the same, it is likely due
to genetics. If intelligence is different,

12. Analyzing Twin Study Results
Extraverted
Neurotic
Agreeable
Conscientious
Correlation (How strongly twins shared the same traits)
0 0.1 0.2 0.3 0.4 0.5
Identical Twins (99% DNA match) Fraternal Twins (50% DNA match)
Open to New
Experiences

13. Analyzing Twin Study Results
Extraverted
Neurotic
Agreeable
Conscientious
Correlation (How strongly twins shared the same traits)
0 0.1 0.2 0.3 0.4 0.5
Identical Twins (99% DNA match) Fraternal Twins (50% DNA match)
Open to New
Experiences
We compare hundreds of
sets of identical twins to see
if they are both extroverted.
52% of twins strongly share
this same trait.
We compare hundreds of
sets of fraternal twins to see
if they are both extroverted.
18% of twins strongly share
this same trait.

14. Analyzing Twin Study Results
Extraverted
Neurotic
Agreeable
Conscientious
Correlation (How strongly twins shared the same traits)
0 0.1 0.2 0.3 0.4 0.5
Identical Twins (99% DNA match) Fraternal Twins (50% DNA match)
Open to New
Experiences
This means that if you have the
same genes, you are more likely to
share the trait of extroversion.
Researchers conclude that
extroversion is notably heritable.

15. Pair-Share
Do you think a Twin Study is a reliable way to
test whether our behavior is determined more
by nature (genetics) or nurture (environment)?
Why or why not?

16. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
For many traits, it seems that we are born with a range of
possibility (a maximum low and a maximum high).

17. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
Nature (genes) determines the maximum expression of a
trait, and the minimum expression of a trait.
Each person will be born with a different capacity for each
trait or ability.

18. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
This is Katie’s genetic potential for intelligence.

19. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
This is Leo’s genetic potential for intelligence.

20. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
Let’s pretend that the yellow box represents the potential
range for intelligence that Sally was born with.

21. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
However, Nurture is what determines how the trait
develops within that range during our lives.
Let’s look at how Sally’s intelligence might develop in two
different environments.

22. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
Sally’s parents read to her every night when she is young.
They provide her with activities at a young age to help her
think and explore.
Sally goes to a nice school and has friends who encourage
her to study.
Sally’s intelligence at age 18

23. Genes & Environment Together
Very low
intelligence
Low
intelligence
Average
intelligence
High
intelligence
Very high
intelligence
Sally’s parents don’t encourage reading. They are poor, and
don’t have enough time to spend with her.
Sally goes to a school that doesn’t receive enough
government funding, and her friends don’t care about
academics, so they distract sally from her studies.
Sally’s intelligence at age 18

24. Genes & Test Scores
In a recent study at University college London, researchers
compared test scores of high school students to their genes.
The study found that 58% of the variation on student test
scores was due to genetic factors.
The research drew
on the exam scores
of more than 11,000
16-year-olds.
Researchers also
compared the scores
of identical and non-
identical twins in a
supplementary study.

25. Nature? (Genetics) or Nurture? (Environment)
Study:
Novelty-seeking
behavior (impulsive
decision-making, the
need to explore,
adventurousness) is
related to the
presence of a certain
gene in the body, and
is highly inheritable.
(Golimbet et al., 2007).
Other Studies
That relate to the “nature, nurture” question

26. Genes & Environment Together
Very low
novelty-
seeking
behavior
Low
novelty-
seeking
behavior
Average
novelty-
seeking
behavior
High
novelty-
seeking
behavior
Very high
novelty-
seeking
behavior
Nature & Nurture work together to determine many of
our personality traits and abilities.
Limitations of nature

27. Which traits are highly heritable?
Openness (Sharing your thoughts/feelings) = .57
Extraversion = .54
Positivity (focus on positive emotions) = .50
Conscientiousness (being careful and thoughtful) = .49
Neuroticism (being moody, worried, anxious) = .48
Negativity (focus on negative emotions) = .44
Aggression = .42
Artistic = .39
Social = .37
Investigative = .36
Realistic = .36
Enterprising = .31
Genetic Influence on Human Psychological Traits, 2004 /. http://www18.homepage.villanova.edu/diego.fernandezduque/Teaching/
PhysiologicalPsychology/zCurrDir4200/CurrDirGeneticsTraits.pdf

28. Interaction of Nature & Nurture
I give you a trait that is highly heritable, and you
tell me how nurture (environment) could also
impact the development of that trait.
#1 Openness

29. Interaction of Nature & Nurture
I give you a trait that is highly heritable, and you
tell me how nurture (environment) could also
impact the development of that trait.
#1 Openness
#2 Agression

30. Schizophrenia is a mental disorder
characterized by a failure to understand
reality. Schizophrenics often feel paranoid and
confused.They see and hear things that aren’t
really there (hallucinations and voices).
Which disorders are highly heritable?
Schizophrenia = .80
Alcoholism = .50
Antisocial behavior (behavior which causes, or is likely to
cause, harassment, alarm or distress to others) = .41
Panic attacks = .30 - .40
Anxiety = .30
Phobias = .20 - .40

31. Genes & Success
Does having amazing genes lead to future
career success and wealth?
This boy had genius
parents.
Do you think his genes
will have a greater
impact on his life, or his
environment will?

32. Genes & Success
Studies show that for children living
in poverty, it did not matter whether
they had good genes or not.The
negative impact of the environment
almost always played a greater role
in their future success than their
genes.
For children in middle class and
wealthy homes, having good genes
became very important to
determining their future success.
Genes played a much greater role in
the future success of each child.

33. Genes & Success
Researchers concluded that for children in harsh living
conditions, it is harder for exceptional genes to “shine through.”
(EricTurkheimer, 2003)

34. Feral Children
Feral Children
are those who
lived away from
human contact
from a very
young age, and
have little or no
experience of
human care,
loving or social
behavior, or
human language.

35. Feral Children
Homework:
Investigate it yourself:
What can we learn from
Feral Children about nature
vs. nurture?
Research at least one feral
child, and write a paragraph
(at least 5 sentences) about
what feral children can teach
us about nature vs. nurture.
Also write 2 discussion
questions.
Examples:
Genie Wiley
Oxana Malaya
Kamala & Amala
Prava the Bird Boy
…