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Life-Span Development
Twelfth Edition
Chapter 2:
Biological Beginnings
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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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 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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 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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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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 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 nongenetic factors inside and outside the body
 Genetic expression is affected by the environment
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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
• XX = female, XY = male
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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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a person’s genetic material
 Phenotype: observable characteristics
 Genotype:
• 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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 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
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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 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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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
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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 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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©2009 The McGraw-Hill Companies, Inc. All rights reserved.
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.
 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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– Environment Correlations:
individuals’ genes may influence the types of
environments to which they are exposed
 Heredity
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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
©2009 The McGraw-Hill Companies, Inc. All rights reserved.