1. Chapter 2: Biological Beginnings
Life-Span Development
Twelfth Edition
Chapter 2:
Biological Beginnings
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Natural Selection
Natural Selection: an evolutionary process by which those individuals of a species that are best adapted are the ones that survive and reproduce
Based on Darwin’s theory
Survival characteristics are passed on in genes
Can produce a gradual modification of the population over many generations
Survival characteristics may change based on environmental conditions
Adaptive Behavior: behavior that promotes an organism’s survival in the natural habitat
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3. Evolutionary Psychology
Evolutionary Psychology: emphasizes the importance of adaptation, reproduction, and “survival of the fittest” in shaping behavior
Fit: the ability to bear offspring that survive long enough to bear offspring of their own
Natural selection favors behaviors that increase reproductive success
David Buss is a very influential evolutionary psychologist
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4. Evolutionary Developmental Psychology
Extended childhood period allows time to develop a large brain and learn complexity of human society
Many evolved psychological mechanisms are domain-specific
Information processing
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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6. Evolution and Life-Span Development
Why do humans live so long after reproduction?
Perhaps older people improve the survival rate of babies
Paul Baltes: benefits of evolutionary selection decrease with age
Natural selection is tied to reproductive fitness
Does not weed out harmful conditions that appear among older adults
Increases our need for culture
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7. Evaluating Evolutionary Psychology
Evolutionary psychology approach is just one theory of many
It has its limitations and weaknesses, and its critics
Bidirectional view: environmental and biological conditions influence each other
Evolution gives us bodily structures and biological potentialities, but it does not dictate behavior
People create behavior in the context of culture
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Genetic Foundations
Human life begins as a single cell
Nucleus of each cell contains chromosomes
Chromosomes: thread-like structures made up of DNA
DNA: a complex double-helix molecule that contains genetic information
Genes: units of hereditary information in each chromosome
Genes direct cells to reproduce themselves and to assemble proteins
Proteins: building blocks of cells and regulators that direct the body’s processes
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Genetic Foundations
Each gene has its own unique location on a particular chromosome
Human Genome Project attempted to map the human genome
Genome: complete set of developmental instructions for the making of a human organism
Results indicated that humans have about 20,000 to 22,000 genes
Humans have far more proteins than they have genes
Genes collaborate with each other and with non-genetic factors inside and outside the body
Genetic expression is affected by the environment
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Genetic Foundations
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Genes and Chromosomes
All cells in the human body (except sperm and egg) have 46 chromosomes arranged in 23 pairs
Mitosis: reproduction of cells
Nucleus (including chromosomes) duplicate, and the cell divides
Meiosis: cell division that forms sperm and eggs (gametes)
Each cell divides twice, forming four cells with 23 unpaired chromosomes
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Genes and Chromosomes
Fertilization: fusing of sperm and egg to create a zygote
Creates one set of paired chromosomes (23 from each parent)
Child’s sex determined by 23rd pair of chromosomes
XX = female, XY = male
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13. The Genetic Difference Between Males and Females
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14. Sources of Variability
Combining genes of both parents increases genetic variability
Chromosomes in zygote are not exact copies
Identical (monozygotic) twins develop from a single zygote that splits into two
Fraternal (dizygotic) twins develop from separate eggs and sperm
Gene mutations can permanently alter segments of DNA
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Genetic Principles
Genotype: a person’s genetic material
Phenotype: observable characteristics
A range of phenotypes can be expressed for each genotype
Dominant-Recessive Genes Principle: a dominant gene always exerts its effects, overriding the potential influence of the recessive gene
A recessive gene only exerts influence if both genes in a pair are recessive
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Genetic Principles
Sex-linked genes:
X-linked inheritance occurs when a mutated gene is carried on the X chromosome
More likely to affect males than females
Females have a second X chromosome, which is likely to be unchanged
Men do not have a second X chromosome to counteract the effect
Females are still carriers
Examples: hemophilia and fragile-X syndrome
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Genetic Principles
Genetic Imprinting: occurs when genes have differing effects depending on whether they are inherited from the mother or the father
Polygenetic Inheritance: characteristics that are determined by the interaction of many different genes
Most characteristics are determined in this manner
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18. Chromosomal Abnormalities
Chromosome abnormalities usually involve the sperm and ovum lacking a normal set of 23 chromosomes
Down syndrome: caused by the presence of an extra copy of chromosome 21
Sex-linked abnormalities involve the presence of an extra X or Y chromosome (or the absence of one)
Klinefelter syndrome: males born with XXY 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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19. Chromosomal Abnormalities
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20. Gene-Linked Abnormalities
Gene-linked abnormalities are caused by harmful genes
PKU: inability to metabolize phenylalanine
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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21. Gene-Linked Abnormalities
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22. Dealing with Genetic Abnormalities
Every individual carries DNA variations, but most do not display a disorder
Today, many genetic diseases can be detected prior to and immediately after birth
However, knowledge of genetic flaws leads to difficult choices about how to manage such information
Genetic counselors help people make reproductive decisions
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23. Prenatal Diagnostic Tests
Ultrasound Sonography: high-frequency sound waves used to create a visual representation of fetus’s inner structures
Fetal MRI: magnetic resonance imaging designed to diagnose fetal malformations
Chorionic Villus Sampling: small sample of placenta is removed to detect genetic and chromosomal abnormalities
Amniocentesis: samples amniotic fluid to test for chromosomal or metabolic disorders
Maternal Blood Screening: identifies pregnancies with elevated risk for certain birth defects
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24. Infertility and Reproductive Technology
Infertility: the inability to conceive a child after 12 months of attempting
In Vitro Fertilization (IVF): egg and sperm are combined in a laboratory dish; fertilized egg is transferred to woman’s uterus
Success depends on woman’s age
Increases risk of multiple births
Higher risk of life-threatening problems
Health risks to mother
Possible psychological effects on children
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25. Infertility and Reproductive Technology
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26. Infertility and Reproductive Technology
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27. Infertility and Reproductive Technology
Adoption: an alternative to infertility treatment
Children adopted early in life fare better than children adopted later
Somewhat more likely to experience psychological and school-related problems than non-adopted children
No differences in antisocial behavior or self-esteem
Vast majority of adopted children adjust effectively, and most parents are satisfied with their decision to adopt
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Behavior Genetics: seeks to discover the influence of heredity and environment on individual differences in human traits and development
Twin studies: compare identical (monozygotic) twins with fraternal (dizygotic) twins
Adoption studies: compare the characteristics of adopted children with their adoptive parents and their biological parents
May also compare adopted and biological siblings
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Heredity – Environment Correlations: individuals’ genes may influence the types of environments to which they are exposed
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Behavioral Genetics
Shared environmental experiences: siblings’ common experiences
Non-shared environmental experiences: a child’s unique experiences, both within and outside the family
Shared environment accounts for little of the variation in children’s personality or interest
Heredity influences the non-shared environments through heredity–environment correlations
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The Epigenetic View
Epigenetic view: development is an ongoing, bi-directional interchange between heredity and environment
Heredity and environment operate together
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Conclusions
The relative contributions of heredity and environment are not additive
Complex behaviors have some genetic loading that gives people a propensity for a particular developmental path
Our environment is complex, and 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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