Chapter 2:Chapter 2:Biological BeginningsBiological Beginnings

Life-Span Development

Twelfth Edition

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Natural Selection: an evolutionary process by which those individuals of a species that are best adapted are the ones that survive and reproduce• $$ The study of human evolution was put forth by Charles

Darwin• 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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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

• $$ Evolutionary developmental psychology suggests that the way in which people develop is adaptive

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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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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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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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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 that are

comprised of short segments of DNA• 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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Each gene has its own unique location on a particular chromosome• Results indicated that humans have about 20,000 to 22,000 genes

Genes collaborate with eachother and with non-genetic factorsinside and outside the body Genetic expression is affected by the environment

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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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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

• XY = male XX = female

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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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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 Imprinting: 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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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• Turner syndrome: females born with XO rather than XX,

sometimes causing infertility• XYY syndrome: males with extra Y chromosome

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Fragile X syndrome• $$ is usually characterized by some sort of mental deficiency. This deficiency could include having:a. mental retardation.b. a short attention span &c. a learning disability.

•occurs more often in males than females; X chromosome constricted or breaks off

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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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$$ Ultrasound Sonography: high-frequency sound waves are directed into the woman's abdomen

1. 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

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$$ Maternal Blood Screening: identifies pregnancies with elevated risk for certain birth defects; such as both Down syndrome and spina bifida

Down Syndrome: genetic disorder that causes lifelong mental retardation, developmental delays and other problems. The cause of Down syndrome is one of three types of abnormal cell division involving chromosome 21.

Spina Bifida: a portion of the neural tube fails to develop or close properly, causing defects in the spinal cord and in the bones of the backbone.

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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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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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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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Epigenetic view: development is an ongoing, bi-directional interchange between heredity and environment• Heredity and environment operate together

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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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