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Chapter 3:
Biological
Beginnings
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2. The Evolutionary Perspective
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Natural selection is evolutionary a process:
Based on Darwin’s theory.
Best-adapted members of species survive to reproduce.
Survival characteristics passed on in genes.
Ideas explain behavior in evolutionary psychology approach.
David Buss: evolution shapes our physical features, and how we make life decisions.
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Evolutionary developmental psychology:
Extended juvenile period allows brain to develop and learn complexity of social interactions.
Many aspects of childhood are preparation for adulthood evolving over time.
Some childhood characteristics promote adaptation during development before reaching adulthood.
Many evolved psychological mechanisms are domain-specific or specific to environmental needs.
Evolved mechanisms are not always adaptive in contemporary society.
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Brain Sizes of Various Primates and Humans in Relation to Length of Juvenile Period
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Evaluating evolutionary psychology:
Evolutionary psychology approach has its limitations and weaknesses, and its critics.
Evolution gives us bodily structures and biological potentialities, but it does not dictate behavior—people do in the context of culture.
Evolved mechanisms are not always adaptive—many behaviors of our ancestors do not serve us well today.
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Genetic Foundations
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Genetic process:
Human life begins as a single cell.
Nucleus of each cell contains DNA.
DNA carries genetic information in double-helix.
Genes are units of hereditary information in each chromosome.
Human Genome Project mapped the human genome and found that it included only about 20,000 to 25,000 genes.
Project found that humans have more proteins than they have genes.
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9. Cells, Chromosomes, Genes, and DNA
The body contains trillions of cells
Nucleus (center of cell) contains chromosomes and genes
A gene, a segment of DNA (spiraled double chain) containing the hereditary code
Chromosomes are threadlike structures composed of DNA molecules
Figure 3.3
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All cells in human body (except the sperm and egg) have 46 chromosomes arranged in 23 pairs.
Meiosis forms sperm and eggs (gametes).
Fertilization: fusing of sperm and egg to form one set of paired chromosomes (offspring gets half of its genes from each parent).
Child’s sex determined by 23rd pair of chromosomes.
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11. The Genetic Difference Between Males and Females
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Genotype: a person’s genetic material containing:
Phenotypes: observable or physical characteristics such as height, body style, and psychological characteristics such as personality and intelligence.
Dominant genes in each pair have the most influence on characteristics unless the pair contains two recessive genes which will have a dominant effect.
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Sex-linked genes:
X-linked diseases and mutations such as hemophilia and fragile-X syndrome.
Females have a second X chromosome so chances of having mutation or disease are less, BUT they are carriers of it.
Males have no second chance; more males than females have X-linked diseases.
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How Brown-Haired Parents Can Have a Blond-Haired Child B
Brown hair
Blond hair b
The gene for blond hair is recessive.
Father
B b
Mother
B b
B B
b b
B b
b B
Figure 3.6
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Chromosome abnormalities usually involve the sperm and ovum lacking a normal set of 23 chromosomes:
Down syndrome—caused by presence of extra copy of chromosome 21.
Sex-linked abnormalities involve presence of extra chromosome or absence of one:
Klinefelter syndrome: males born with XXY mutation instead of XY.
Fragile X syndrome: occurs more often in males than females; X chromosome constricted or breaks off.
Turner syndrome: females born with XO rather than XX, sometimes causing infertility.
XYY syndrome: males with extra Y chromosome.
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Gene-linked abnormalities:
PKU: occurs in 1 out of 10,000-20,000 births but can be treated if detected early enough.
Sickle-cell anemia: impaired red blood cells die more quickly; more often found in African Americans.
Other abnormalities: cystic fibrosis, diabetes, spina bifida, Huntington disease, and Tay-Sachs disease.
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17. Dealing with Genetic Abnormalities
Everyone has genetic flaws, but most don’t cause disorders.
Today, genetic flaws can be detected prior to and after birth.
But knowledge of genetic flaws brings hard choices about what to do with the information.
Genetic counselors help people make reproductive decisions.
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18. Challenges and Choices
Reproductive
Challenges and Choices
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Prenatal diagnostic tests:
Amniocentesis: samples amniotic fluid.
Ultrasound sonography: high frequency sound waves used.
Chorionic villus sampling: small sample of placenta is removed during 8th–11th week.
Maternal blood screening identifies pregnancies with elevated risk for birth defects.
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Infertility and reproduction technology:
In vitro fertilization (IVF): egg and sperm united in laboratory dish.
Gamete intrafallopian transfer (GIFT): egg and sperm deposited directly into fallopian tube.
Zygote intrafallopian transfer (ZIFT): eggs fertilized in lab, then zygote deposited into fallopian tube.
Consequences of multiple births:
Higher risks of life-threatening problems.
Health risks to mother.
Psychological effects on children.
Another alternative: adoption.
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Success Rates of Three Different Assisted Reproduction Techniques 10 20 30 40
29.2%
31%
24.5%
ZIFT
IVF
GIFT
There was little variation in success rates based on couples’ ages, so results are combined.
Type of Assisted Reproduction
Figure 3.10
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Socioemotional Functioning of Children Conceived Through In Vitro Fertilization or Naturally Conceived
In vitro fertilization 40
Natural conception 30 20 10
School functioning
Peer relations
Self- esteem
Figure 3.11
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Childrearing challenges after adoption:
Infancy: attachment?
Early childhood: integration into family.
Middle and late childhood: curiosity about real/biological parents.
Adolescence: child’s reflection on adoptive status.
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24. Heredity and Environment Interaction: The Nature-Nurture Debate
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Heredity and environment interact to produce development; each person’s development varies.
Behavior genetics:
Most research based on twin and adoption studies.
Twin studies compare identical (monozygotic) twins with fraternal (dizygotic) twins.
Adoption studies compare child’s traits with those of adoptive and biological parents.
All studies conducted in developed countries only.
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Heredity–environment correlations - genetic propensities influence environment to which individuals are exposed. Sandra Scarr described three such interactions:
Passive genotype-environment correlations—parents raise children in the way in which they are comfortable.
Evocative genotype-environment correlations—child’s characteristics elicit certain types of environments.
Active (niche-picking) genotype-environment— children seek out environments they find compatible and stimulating.
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Examples:
Intelligent biological parents who like to read provide books and encouragement for child to read – likely outcome is skilled reader (passive).
Active, smiling, cooperative, and attentive child gets more pleasant, encouraging responses from adults than passive, quiet child (evocative).
Some children actively seek out aspects of their environment that enhance their ability to excel (active).
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Siblings’ shared and nonshared environmental experiences analyzed 2 ways:
Shared experiences examined as common experiences like family SES, parental personalities, and neighborhood.
Nonshared experiences examined as child’s unique experiences inside & outside family not shared by siblings:
Personal relationship with each parent.
Friends and classmates.
Teachers and other influential adults.
“Niches” sought out due to unique personality traits (musical/artistic abilities).
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Epigenetic view: development is an ongoing, bi-directional interchange between heredity/genetics and environment.
Example: baby has inherited genes but is exposed to toxins during prenatal development.
Outcome can change genetic development during the prenatal or infancy period.
Such an example can impact on the nature vs nurture debate.
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Comparison of the Heredity–Environment Correlation and Epigenetic Views
Heredity–environment correlation view
Heredity
Environment
Epigenetic view
Heredity
Environment
Figure 3.14
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31. Conclusions about Heredity-Environment Interaction
Complex behaviors have some genetic loading that gives people a propensity for a particular developmental path.
Our environments are complex.
The interaction of heredity and environment is extensive.
Much needs to be learned about specific ways in which environment and genetics interact to influence development.
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