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Anthropology
Appreciating Human Diversity
Fifteenth Edition
Conrad Phillip Kottak
University of Michigan
McGraw-Hill
© 2013 McGraw-Hill Companies. All Rights Reserved.
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EVOLUTION
AND GENETICS
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EVOLUTION AND GENETICS
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Evolution
Genetics
Biochemical, or Molecular, Genetics
Population Genetics and
Mechanisms of Genetic Evolution
• The Modern Synthesis
5-3
EVOLUTION AND GENETICS
• What is evolution, and
how does it occur?
• How does heredity work,
and how is it studied?
• What forces contribute
to genetic evolution?
5-4
EVOLUTION
• Humans have uniquely varied ways—cultural
and biological—of adapting to environmental
stresses
• Many scholars became interested in
biological diversity and our position within the
classification of plants and animals during the
18th century
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EVOLUTION
• Creationism: biological similarities and
differences originated at the Creation
• Linnaeus (1707–1778) developed the
first comprehensive and still influential
classification, or taxonomy, of plants and
animals
• Fossil discoveries during the 18th and 19th
centuries raised doubts about creationism
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EVOLUTION
• Catastrophism: modified version of
creationism that accounts for the fossil record
by positing divinely authored worldwide
disasters that wiped out creatures
represented in the fossil record
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THEORY AND FACT
• Evolution: transformation of species;
descent with modification
• Alternative to creationism and catastrophism
• Darwin best known of evolutionists
5-8
THEORY AND FACT
• Darwin influenced by:
• Theory of evolution – belief that species arise from others
through a long and gradual process of transformation; all life
forms are related and the number of species has increased over
time
• Grandfather, Erasmus Darwin, who proclaimed
a common ancestry of all animal Lyell’s principle of
uniformitarianism:
the present is the key to the past; past geological events can
bets be explained by observing ongoing events of the present
and generalizing backward through time
• Darwin applied uniformitarianism to living things; contributed a
theory of evolution through natural selection
5-9
THEORY AND FACT
• Darwin proposed natural selection to explain the origin of the
species, biological diversity, and similarities among related life forms
• Reached the conclusion along with Alfred Wallace
• Natural selection: the process by which nature selects the forms
most suited to survive and reproduce in a given environment
• Variety within that population
• Competition for strategic resources
• Giraffes – long versus short necks
• Argues that organisms that have a better fit within their
environment, will reproduce more frequently than those less fit
• Reproduction is the key
• Natural selection continues today
• Peppered moth
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GENETICS
• Genetic science helps explain causes/origin
of biological variation
• Mendelian genetics: ways in which chromosomes
transmit genes across generations
• Biochemical genetics: examines structure,
function, and changes in DNA
• Population genetics: investigates natural
selection and the causes of genetic variation,
stability, and change
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MENDEL’S EXPERIMENTS
• Austrian monk Gregor Mendel began series
of experiments that revealed basic principle
of genetics in 1856
• Studied inheritance of seven contrasting traits
in pea plants
• Concluded that heredity is determined by discrete
particles or units (genes) that may disappear in
one generation and reappear in the next
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MENDEL’S EXPERIMENTS
• Observed two traits: dominant and recessive
• Dominant forms appear in each
generation/recessive forms are masked when
paired with dominant form of same trait
• Concluded that a dominant form could mask
another form in hybrid individuals, without
destroying the recessive trait
• Basic genetic units Mendel described were
factors (now called genes or alleles) located
on chromosomes
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MENDEL’S EXPERIMENTS
• Chromosome: a paired length of DNA,
composed of multiple genes
• Gene: a place (locus) on a chromosome that
determines a particular trait
• Allele: a variant to a particular gene
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MENDEL’S EXPERIMENTS
• Heterozygous: dissimilar alleles of a gene in
an offspring
• Homozygous: two identical alleles of a gene
in an offspring
• Genotype: organism’s hereditary makeup
• Phenotype: evident biological traits
• Dominance produces a distinction between
genotype and phenotype
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INDEPENDENT ASSORTMENT
AND RECOMBINATION
• Independent assortment: traits are inherited
independently of one another
• Recombination: traits may appear in new
combinations with other traits; new types in
an offspring on which natural selection can
operate; two main ways produces variety
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Figure 5.1: Mendel’s Second Set
of Experiments with Pea Plants
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Figure 5.2: Simplified Representation of a
Normal Chromosome Pair
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Figure 5.3: Punnett Squares of a
Homozygous Cross and a Heterozygous Cross
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Figure 5.4: Determinants of Phenotypes
(Blood Groups) in the ABO System
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BIOCHEMICAL, OR MOLECULAR,
GENETICS
• Mutation: changes in the DNA molecules of which
genes and chromosomes are built; produces variety
(source of new forms on which natural selection may
operate)
• DNA:
• Can copy itself, which forms new cells that replace
old ones
• Produces the gametes: sex cells that make new
generations
• Guides the body’s production of proteins
BIOCHEMICAL OR MOLECULAR GENETICS
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BIOCHEMICAL, OR MOLECULAR,
GENETICS
• DNA molecule is a double helix
• Structure of RNA, with paired bases,
matches DNA
• Proteins are built following instructions sent by DNA with the
assistance of RNA
• RNA carries DNA’s message to cytoplasm
(outer area)
• A protein, or chain of amino acids, is constructed by “reading”
RNA’s bases (triplets)
• DNA, with RNA’s assistance, initiates and guides the
construction of proteins necessary for bodily growth,
maintenance, and repair
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Figure 5.5: DNA Replication
5-23
CELL DIVISION
• Mitosis: ordinary cell division; one cell splits to form two identical
cells
• Mistakes in this process of cell division, including chromosomal
breaks and rearrangements, can cause diseases such as cancer
• Meiosis: process that produces sex cells
• Four cells produced from one
• Each cell carries half genetic material of
original cell
• Products of meiosis from one parent combine with those from
the other parent
• Chromosomes sort independently
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CROSSING OVER
• Crossing over:
• Chromosomes temporarily intertwine in the
course of reduplication and exchange lengths of
their DNA
• the process wherein homologous chromosomes
exchange segments by breakage and
recombination
• Can occur with any chromosome pair
• An important source of variety on which natural
selection operates
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Figure 5.6: Crossing Over
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MUTATION
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Mutations: the most important source of variety upon which natural
selection acts
Base substitution mutation: substitution of one base in a triplet by another
Chromosomal rearrangement: pieces
of a chromosome break off and reattach someplace else on that
chromosome
• A mismatch of chromosomes resulting from arrangement can lead to
congenital disorders, cancer, and possibly to speciation
Chromosomes may also fuse:
• When ancestors of humans split off from those of chimpanzees around
six milion years ago, two ancestral chromosomes fused together in the
humans line
• Humans have 23 chromosome pair versus 24 for chimps
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MUTATION
• Approximately three mutations will occur in
every sex cell
• Most mutations are neutral
• Evolution depends on mutations
• Mutations are major source of genetically
transmitted variety
• Mutations may be neutral, harmful, or acquire an
adaptive advantage through changing selective
forces
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POPULATION GENETICS AND
MECHANISMS OF GENETIC EVOLUTION
• Population genetics studies stable and changing
populations
• Gene pool: alleles and genotypes within
breeding population
• Genetic evolution: change in allele frequency
in a breeding population
There are four basic mechanisms that produce changes
in gene frequency in a population: natural selection,
mutation (already discussed), random genetic drift, and
gene flow.
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NATURAL SELECTION
• Genotype: the genetic makeup of an organism
• Phenotype: organism’s biological traits (outward physical
appearance as well as internal organs, tissues, and cells
and physiological processes and systems)
• Natural selection acts only on phenotypes
• Human biology has considerable plasticity
• The environment works on a genotype to build
a phenotype
• Diet and altitude affect how a person grows
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DIRECTIONAL SELECTION
•
After several generations of selection,
gene frequencies change
• Adaptive traits (favored by natural selection) will be selected from generation to
generation
• Directional selection (long-term selection of same traits) continues as long as
environmental sources stay the same
• Maladaptive alleles removed from gene pool
• If environment changes, new selective forces start working, favoring different
phenotypes
• Selection operates only on traits that are present in a population
• Favorable mutation may occur but doesn’t usually happen just because one
is needed or desirable; many species are extinct because they couldn’t
adapt to environmental shifts
• Humans adapt rapidly to environmental variation by modifying biological
responses and learned behavior
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SEXUAL SELECTION
• Selection also
operates through
competition for mates
• Sexual selection:
based on differential
success in mating;
a selection of traits
that enhances
mating success
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STABILIZING SELECTION
• Balanced polymorphism:
frequencies of two or
more alleles of a gene
remain constant from
generation to generation
• Homozygous HbA produces normal hemoglobin
• Homozygous HbS produces sickle-cell anemia
• Heterozygosity for this gene produces the harmful but nonlethal
sickle-cell syndrome
• Africa, India, and Mediterranean
• Traits that are maladaptive in one environment, can be adaptive
in a different environment (and visa versa)
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Figure 5.7:Distribution of Sickle-Cell
Allele and Falciparum Malaria in the Old World
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RANDOM GENETIC DRIFT
• Random genetic drift: change in allele
frequency that results from chance
• Alleles can be lost by chance rather than because
of any disadvantage they confer
• Lost alleles can reappear in gene pool only
through mutation
• Fixation—the replacement, for example, of blue
eyes by brown eyes—is more rapid in small
populations
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GENE FLOW
• Gene flow: exchange of genetic material between populations of the
same species
• Direct or indirect interbreeding
• Allele that isn’t advantageous in one environment might reach an
environment in which it has selective advantage
• Alleles spread through gene flow even when selection not
operating on the allele
• Species: group of related organisms whose members can
interbreed to produce offspring that live and reproduce
• Gene flow tends to prevent speciation:
the formation of new species
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Figure 5.8: Gene Flow between Local Populations
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THE MODERN SYNTHESIS
• Currently accepted view of evolution:
• Modern Synthesis: combination of Darwin’s theory of evolution
by natural selection and Mendel’s genetic discoveries
• Speciation occurs when related populations become
reproductively isolated from one another
• Microevolution: small-scale changes in allele frequencies over
just a few generations, but without speciation
• Macroevolution: large-scale changes in allele
frequencies in a population over a longer time period, which
result in speciation
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PUNCTUATED EQUILIBRIUM
•
Punctuated equilibrium: long periods of stasis (stability) may be interrupted by
evolutionary leaps (revealed in fossil record)
• Occurs through:
• Extinction of one species followed by invasion of closely related species
• Replacement of one species by a more fit related group in particular
environment
• Period of sudden environmental change that permits survival of radically
altered species with significant mutations or a combination of genetic
changes
• Sudden environmental change offers possibility for the pace of evolutions to
speed up
• Species can survive radical environmental shifts, but extinction is more common
• Extinction of dinosaurs was accompanied by rapid spread of mammals and
birds
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