Transcript Evolutionary Anthropology

ANG 6930
Proseminar in
Anthropology IIA:
Bioanthropology
Day 3
ANG 6930
Prof. Connie J. Mulligan
Department of Anthropology
Next week
Genetics and the development of evolutionary theory
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Mendelian and molecular genetics
Population genetics
Evolutionary development biology (Evo Devo)
Reading
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The Human Species, Chpts 2 (Human genetics), 3 (Evolutionary
forces), 8 (Paleoanthropology)
Course packet
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Tattersall I. 2000. Paleoanthropology: The last half-century.
Evolutionary Anthropology 9:2-16
Foley R. 2001. In the shadow of the modern synthesis? Alternative
perspectives on the last fifty years of paleoanthropology. Evolutionary
Anthropology 10:5-14
Carroll SB. 2003. Genetics and the making of Homo sapiens. Nature.
422:849-857
“Beyond Stones and Bones”, Newsweek, March 19, 2007.
Topic and abstract for journal analysis is due
First set of questions/comments is due
Next week
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Primate evolution, ecology and behavior
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Primatology as anthropology
Diversity of living primates
Primate models for human evolution and behavior
Comparison of humans and other primates
Reading
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The Human Species, Chpts 5 (Primates), 6 (Primate behavior and ecology),
7 (The human species)
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Course packet
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Martin RD. 2002. Primatology as an essential basis for biological
anthropology. Evolutionary Anthropology 11:3-6.
Strier KB. 2003. Primate behavioral ecology: From ethnography to
ethology and back. American Anthropologist 105:16-27.
Rieseberg LH and Livingstone K. 2003. Chromosomal speciation in
primates. Science 300:267-268.
Khaitovich P et al. 2005. Parallel patterns of evolution in the genomes and
transcriptomes of humans and chimpanzees. Science 309:1850-1854.
Amici et al. 2010. Monkeys and apes: Are their cognitive skills really so
different? American Journal of Physical Anthropology 143: 188-197.
Judson O. 2008. Wanted: Intelligent aliens, for a research project, New
York Times blog
Journal analysis
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Once you choose your topic, you will write a paper (~10
pages, double-spaced) that discusses how your topic was
addressed in the five journals over that past 15 years
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An important point will be to examine how bioanthropology and
another subfield of anthropology cover your topic, e.g. what are the
important questions being addressed/hypotheses being tested,
what are the interpretations and conclusions, are there major
differences in interpretations/conclusions?
Compare coverage of your topic in three ways: 1) across five
journals, 2) through time, and 3) between two subfields. Be
EXPLICIT in your comparisons. This is not an explanation of your
topic or a review of the literature, but an explicit comparison of
coverage/treatment of your topic in the three ways listed above.
Provide # articles/journal, talk about how the questions addressed
differ through time, by subfield, etc
The final paper is due at our last class, Feb 18.
Quiz 1
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Average – 8.12, two 10s
http://www.clas.ufl.edu/users/cmulligan/Webp
age/Proseminar.2011/Quiz1answers.htm
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Difference between Lamark and Darwin, acquired
vs inherited variations/adaptations
Genetics and the
Modern Synthesis
Timeline of Key Developments
1859 Darwin lays out the theory of natural selection in his On the
Origin of Species.
1866 Mendel publishes findings on laws of inheritance; posits
“Elementes” as unit of heredity.
1882 German biologist Walter Fleming, by staining cells with
dyes, discovers rod-shaped bodies he calls "chromosomes."
1902 American biologist Walter Sutton shows that chromosomes
exist in pairs that are similar in structure. In light of Mendel's
theory that genetic "factors" segregate, he concludes that
hereditary factors must lie on chromosomes.
Timeline of Key Developments
1915 Thomas Hunt Morgan, an American geneticist, presents
results from experiments with fruit flies that prove genes are lined
up along chromosomes. He also describes the principle of “linkage”
and lays the groundwork for gene mapping.
1944 Avery, MacLeod, and McCarty report that
the molecule that carries genetic
information is
deoxyribonucleic acid (DNA)
1953 Crick and Watson determine that the structure of
the DNA molecule is a double helix formed by strands of
sugar and phosphate molecules joined by the bonding of
four bases
Darwin’s Postulates
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Infinite ability of populations to grow, but finite
ability of environments to support growth
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Within populations, organisms vary in ways
that affect ability to survive and reproduce
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Variations are transmitted from parents to
offspring
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Natural selection – evolution by variation and
selective retention
Darwin’s Difficulties
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Blending inheritance
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Cannot explain how variation is maintained
Favors selection of discontinuous traits, not
accumulation of small changes
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Natural selection removes variation
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Natural selection cannot explain variation
beyond original range
Gregor Mendel (1822-1884)
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Austrian monk in
present-day Slovakia
Experiments with truebreeding garden peas,
1856-1863
Published in 1866, but
not widely read or
understood
Rediscovered in 1900
by Hugo de Vries and
Carl Correns
Green
parents
Yellow
parents
GG
YY
F1 generation:
all yellow
GY
GY
F2 generation:
3 yellow
1 green
Green
parents
Yellow
parents
GG
YY
F1 generation:
all yellow
GY
GY
F2 generation:
3 yellow
1 green
GG
GY
GY
YY
Mendel’s Insight
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Organism’s visible characteristics do not always represent heritable
qualities
 Genotype  phenotype
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Hereditary qualities are nonreducible particles, not blended in sexual
reproduction
 Mendelian inheritance
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Yellow peas can produce green peas
Each ‘particle’ retains its characteristic though it may not manifest in an
individual, i.e. a green gene is still a green gene even if the plant is not green
Hereditary particles generally function as pairs
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Transmission of pea characteristics only works if he has two ‘particles’ to
work with in each individual, i.e. recessive and dominant traits
Mendel’s Hereditary Principles
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Principle of particulate heredity
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Principle of segregation
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Heredity transmitted by many independent,
nonreducible particles that occur in pairs
Each hereditary pair is split during production of
sex cells, and new pairs are formed by fertilization
Principle of independent assortment
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Hereditary particles for different traits generally
inherited independently
Rediscovery of Mendel
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Hugo De Vries (1848-1935),
Dutch botanist
Suspected mutations as
source of new variation
Replicated Mendel’s insight
in experiments with evening
primrose
De Vries
Chromosomes
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In 1902, Sutton made connection between chromosomes and
Mendel’s principles of heredity
Long strands of DNA in cell nucleus, 23 pairs in humans
Genes
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Genetic equivalent of atom:
fundamental unit of heredity
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DNA is organized into chromosomes
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A locus is a particular site on
chromosome
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An allele is one of several forms of a
DNA sequence
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Gene is a locus that encodes a protein
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The genome is all genes on all
chromosomes in an organisms
DNA
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Invariant sugar-phosphate
backbone
Variable chemical bases that make
up the ladder ‘rungs’
Four complementary bases
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Adenine (A) bonds with thymine (T)
Guanine (G) bonds with cytosine (C)
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Complementary bases are key to
DNA function, i.e. provide variation
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Sequence of bases code for amino
acids that form proteins
DNA Structure Uniquely Suited for
Inheritance
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Nearly infinite variety of messages from
four-base structure
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Structure implies how inheritance works
 Two strands held together by weak
hydrogen bonds, i.e. can be unzipped for
DNA replication or RNA transcription
 DNA replication - Reliably replicates
message by unzipping and using singlestranded template to synthesize new
DNA
 RNA transcription – Again unzips DNA
and uses single-stranded DNA template
to synthesize RNA for protein synthesis
Types of DNA polymorphisms
SNP – single nucleotide
polymorphism
Large insertion
- causes myotonic dystrophy
Microsatellite
= STR (simple
tandem repeat)
= STRP (simple
tandem repeat
polymorpism)
= multiple copies
of a short (2-6bp)
sequence, eg.
CACACACA
Types of DNA
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Mitochondrial (mtDNA)
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no recombination
high copy number (but
haploid)
maternal inheritance
high mutation rate
studied first
large comprehensive
database
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Nuclear DNA (nDNA =
autosomes + sex
chromosomes)
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homologous
recombination
single genome/diploid cell
biparental inheritance
variable mutation rate
studied more recently
multiple studied loci make
comparisons more difficult
PCR - polymerase chain reaction
Kary Mullis – inventor, Nobel prize winner, 1983
1 copy of DNA sequence
Polymerase
chain
reaction
= PCR,
the exponential,
synthetic
amplification of
nucleic acid from a
targeted region of
the genome
Billions of copies of DNA sequence
Mitosis
Meiosis
(Cell division)
(gamete [eggs and sperm]
production)
Diploid
parent cell
Diploid
daughter cells
Diploid
parent cell
Haploid
gametes
Blending inheritance
(not true)
F0 generation
Gametes
F1 generation
Gametes
F2 generation
Mendelian inheritance
(True)
Predicting Offspring Distributions
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Mendel’s principles explain ratio of genotypes in the
offspring of particular parents
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A given allele of each parent has 50 percent chance
of transmittal
Meiosis Is Key To Human Variation
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First, independent assortment leads to differences
among gametes
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Haploid cells (egg or sperm) produced by meiosis
are all genetically different
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Requires selection of either paternal or maternal
copy of each chromosome
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Number of possible combinations of haploid
chromosome subsets is 223 (8,388,608)
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Assuming no recombination
Meiosis Is Key To Human Variation
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Second, recombination (crossingover) creates new combinations of
genetic material
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During meiosis, chromosomes
physically line up
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At certain places, strands join together
and exchange pieces
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Process reshuffles genetic material in
creation of new gametes (egg or
sperm)
Meiotic recombination
Jobling et al. 2004, Fig. 2.17
Assortment and Recombination
Inheritance of recombining and nonrecombining segments of the genome
Jobling et al. 2004, Fig. 2.18
Genotypes and Phenotypes
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One of Mendel’s insights was that phenotype
does not necessarily reflect genotype
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Phenotype – observable trait of individual
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Genotype – set of two alleles at a particular
locus
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Homozygous if both alleles are the same (AA or aa)
Heterozygous if the two alleles are different (Aa)
Genotypes and Phenotypes
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Phenotype determined by relationship
between two alleles at a given locus
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Dominant alleles mask effect of other allele
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Phenotype of AA = phenotype of Aa
If selection favors dominant phenotype, AA and Aa
genotypes are equally favored
Recessive alleles are masked by other allele
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Recessive phenotype only expressed in aa
genotype
Molecular Basis of Recessiveness
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Most recessive disorders result in absence or
severe reduction of gene product
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Example – cystic fibrosis
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Present in homozygous recessive genotype
Sufferers lack protein that helps transport water
across cell membranes → thick and sticky mucus
Heterozygotes are carriers, but do not have
disease
Emergence of the Modern Synthesis
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Modern synthesis – a movement to unify evolutionary biology
under a single conceptual umbrella (1930s-1940s)
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Biologists first thought Mendelian inheritance was incompatible
with Darwinian evolution
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Mendel suggests inheritance fundamentally discontinuous, i.e. two
discrete heritable units
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Darwin emphasize accumulation of small changes
Fisher, Wright, and Haldane worked out mathematical theory to
show how Mendelian inheritance could explain continuous
variation
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Complex vs monogenic phenotypes
Individual Selection
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Selection arises from competition among
individuals, not among populations or species
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Example – individual reproductive success
and species’ survival
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Selection may favor high individual fertility,
even if population growth threatens survival
of species
Evolution and Population
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Evolution involves change in genetic makeup
of populations
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Two scales of evolutionary change
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Macroevolution – evolution of new species
Microevolution – evolution at level of population,
within species
Evolution = change in frequency of alleles in
a population from one generation to the next
Population Genetics
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Modern synthesis  genes in population
Four evolutionary mechanisms (phenomena
that change frequencies of alleles)???
Population Genetics
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Modern synthesis  genes in population
Four evolutionary mechanisms (phenomena that
change frequencies of alleles)
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Mutation
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Natural selection
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Gene flow
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Genetic drift
Microevolutionary mechanisms also underlie
macroevolution
Evolutionary Forces
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Mutation
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Ultimate source of all new genetic variation
Other evolutionary forces alter frequency of new
alleles
Natural selection
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Filters new variation
Analysis focuses on fitness – proportion of
individuals with given genotype who survive to
reproduce
Evolutionary Forces
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Genetic drift
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Random change in allele frequency from one
generation to next
Occurs each generation, reduces variation over
time
Gene flow
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Movement of alleles from one population to
another
Makes populations more similar over time
Genetic Drift
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Genetic drift causes
fixation and elimination
of new alleles
Magnitude of genetic
drift depends on size of
population
Present day variation
depends on past small
population sizes
Genetic drift in
populations of different sizes
Bottlenecks and Founder Effects
Gene Flow
Selection, Drift, Gene Flow, and Variation
Evolutionary
Force
Variation within
Populations
Variation between
Populations
Selection
Increase or
decrease
Increase or
decrease
Genetic drift
Decrease
Increase
Gene flow
Increase
Decrease
Disagree – selection for an advantageous variant will still decrease variation
because it decreases the frequencies of all non-selected variants
Monogenic and Complex Traits
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Mendel’s experiments involved discrete traits
shaped by single locus
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Single-gene (monogenic) traits are not typical
of human variation
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Many traits of interest to us are complex
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Involve multiple genes
Influenced by environment
Follow complex mode of inheritance
Distribution of Continuous Traits
Genotype
Genotypes
Genotypes
Genotypes
Genes and Biological Effects
Hardy-Weinberg Equilibrium
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Genotype and allele frequencies remain
constant over generations
Assumptions
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Random mating
No evolutionary forces
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No mutation
No selection
No genetic drift
No gene flow
Hardy-Weinberg Example
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Recessive monogenic disorder has incidence of 1 in 2500 - what is
frequency of carriers?
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Frequency of AA genotype = p2
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Frequency of Aa genotype = 2pq
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Frequency of aa genotype = q2
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p+q=1
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Equations only possible if genotype and allele frequencies remain constant
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Frequency of recessive allele = q2, therefore q = (0.0004)0.5 = 0.02
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Allele frequencies must sum to 1, therefore p = 1-q = 0.98
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Frequency of heterozygous genotype, i.e. carriers, is
2(0.02)(0.98) = 0.0392, about 1 in 25
2pq =
Significance of Hardy-Weinberg
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Quantitative demonstration that variation is preserved
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No inherent tendency for dominant allele to increase
frequency
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Unifies Darwinian evolution with Mendelian inheritance
Addresses Darwinian idea that dominant alleles should be
most common
Springboard for research into evolutionary forces
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Populations not in Hardy-Weinberg equilibrium are
undergoing microevolutionary change
Chpt 8 – Serial Homology
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Serial homologs – structures that
arose as repeated series, became
differentiated to varying degrees in
different animals
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Huxley (1963)
Evidence as to Man’s Place in Nature
Vertebrae and ribs, forelimbs and
hindlimbs, digits, teeth, etc.
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Changes in number and kind of
serial homologs are key themes in
evolution
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Unique human features result from
developmental changes that
modified existing primate or great
ape structures
Chpt 8 - A Brief History of Life
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Perspectives on Geologic Time
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The universe is roughly 15 billion years old
The earth is about 4.6 billion years old
Two major eons: Precambrian eon (4.6 bya to 545
mya) and Phanerozoic eon (545 mya to present)
A Brief History of Life
The universe is roughly 15 billion years old
The earth is about 4.6 billion years old
Two major eons: Precambrian eon (4.6 bya to 545
mya) and Phanerozoic eon (545 mya to present)
Figure 4.6: Carl
Sagan’s Cosmic
Calendar. The history
of the universe is
compressed into a
single year, with its
origin happening on
January 1 and the
present day occurring
at midnight on the
following January 1.
A Brief History of Life
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Precambrian Eon
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Paleozoic Era
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545 to 245 mya
Origin of first vertebrates, jawless fish
Evolution and diversification of fish, amphibians, and reptiles.
Mesozoic Era
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Beginning of the planet (4.6 billion years ago) to 545 mya
Single-celled and multi-celled organisms first appeared
245 to 65 mya
Age of reptiles, dominated by dinosaurs
First egg-laying mammals (Triassic Period) followed by first placental
mammals (Jurassic Period).
Cenozoic Era
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65 mya to present
Age of mammals
Evolution of primates and humans
Chpt 8 - Dating methods
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Dating fossil remains
Chronometric dating
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Determines an exact age
Relative dating
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Determines which fossils are older, but not their
exact age
Relative dating methods
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Stratigraphy
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Biostratigraphy
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Older remains are found deeper in the earth b/c of
cumulative build-up of the earth’s surface over time
Fossils/sites can be assigned an approximate age based
on the similarity of animal remains with those from other
dated sites
Paleomagnetic reversals
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Uses the fact that the earth’s magnetic field has shifted
back and forth from north to south at irregular intervals
Chronometric dating methods
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Carbon-14 dating
 Absolute dating of carbon-based remains (organic) based on the half-life
of carbon-14 (5,730 yrs), useful over past 50,000 yrs
Potassium argon dating
 Based on half-life of radioactive potassium (1.31 billion yrs), useful for
samples older than 100,000 yrs
Argon-argon dating
 Based on half-life of argon, useful for very small samples
Dendrochronology
 Based on tree ring counts of trees in dry climates where trees accumulate
one growth ring per year
Thermoluminescence
 Certain heated objects accumulate trapped electrons over time, allowing
the date that the object was initially heated to be determined
Electron spin resonance
 Estimates dates from observation of radioactive atoms trapped in calcite
crystals present in materials such as bones and shells, useful less then
300,000 yrs altho can be used over a million yrs
One more chronometric dating method
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Molecular dating
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Use of molecular genetic data to determine genetic distance
between species/populations/etc and calibrate a molecular
clock to determine # differences = # years divergence
Need locus with mutation rate appropriate to question
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Colonization of the New World
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Emergence of modern Homo sapiens
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100s or 1000s of yrs
Divergence of man from non-human primates
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10s of 1000s of yrs
millions of yrs
Example – draw a phylogeny
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Distance b/t species A and B = 3 (bp changes or some other unit)
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Distance b/t species A and C = 30
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Distance b/t species B and C = 30
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Divergence of C from A and B (fossil evidence) = 30 million
yrs ago
Current hot topics on humans
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Top 10 mysteries about humans
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http://www.livescience.com/history/091026-top10origins-mysteries.html
Top 10 things that make humans special
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http://www.livescience.com/culture/091030origins-top10-special.html