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Transcript of Evolution. The unifying theme of biology is 1.A) taxonomy. 2.B) genetics. 3.C) ecology. 4.D)...
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Evolution
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The unifying theme of biology is
1. A) taxonomy. 2. B) genetics. 3. C) ecology. 4. D) evolution. 5. E) None of the choices are correct.
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Figure 13.00b
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Figure 13.00c
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Figure 13.00d
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Evolution
Evolution means change over time
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Outline
• Overview of evolution & natural history• Darwin’s voyage• Evidence for evolution• Natural selection• Population Genetics• Hardy-Weinberg Equilibrium• Microevolution
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The Earth today is not what it once was
• The earth is thought to be 4.5 billion years old
• Life is thought to have appeared ~3.8 billion years ago
• The early atmosphere had methane, carbon monoxide, and
• Essentially no oxygen
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Molecules common to all living things formed on a hot earth which lacked oxygen in its atmosphere
Stanley Miller took early earth ingredients and treated with “lightning” Results- Amino acids; nucleic acids
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The past contains species very diffent from familiar species of today
• Species of the past are radically different from what exists on earth today
• Converse is true- things that exist today are not seen in the past
• The Burgess Shale shows the rapid increase in diversity from the Cambrian explosion, ~530 M.y.a.
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Yet there are connections between species of past and present
• Species of today have physical similarities
• This archaeopteryx fossil shows feathers
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People did not always know the earth was ancient
• Anglican archbishop James Ussher, 1581-1656
• October 23, 4004BC: Earth was created
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Extinction was once only a theory
• Mary Anning, fossil hunter, found a plesiosaur in 1821• Other marine fossils were found several miles from
shore• This and other evidence caused speculation about the
age of the earth
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The Geologist Charles Lyell proposed that the earth was much, much older
• Posited the idea that continents have moved over time
• This is continental drift, caused by plate tectonics
• Continents move very slowly
• Earth must be very old• Darwin carried Lyell’s
book, Principles of Geology (1833), with him on the Beagle
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About 250mya, all continents were joined
• Contients had drifted together
• Continents subequently drifted apart
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Continents can collide to form mountains
• This raises aquatic sediments from ocean bottoms
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Charles Darwin became curious about how species came about
• February 12, 1809- April 19, 1882
• Flunked out of med school• Didn’t much like Divinity
school, either• Became a naturalist aboard
the HMS Beagle• Darwin lived in a time when
science, industry, and society were beginning to progress more rapidly
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The Voyage of the Beagle
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Darwin’s critical observations were comparisons between island species and
mainland species
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Marine Iguana and South American Iguana
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Flightless cormorants live only on the Galapagos
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A Variety of Finches are found in the Galapagos
Finches each have adaptations for different small island environments
They have many other traits in common
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Darwin’s inference: The finches have a single common ancestor
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Likewise, the marine iguanas must have come from the mainland
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Evolution- the change in species over time
• New species are formed from older ancestors
• Some become extinct, others evolve into different species
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But what was the mechanism?
• How did a species change over time?
• Lamarch proposed a mechanism:
-By repeated strain, a giraffe acquires a long neck
-The long neck is inherited by the offspring
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Natural Selection
The mechanism by which life evolves
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Darwin’s Mechanism: Natural selection
• Those best suited for their environment are selected for survival
• Genes are inherited by the next generation
• Better-adapted species pass on genes suited for the environment
• Next generation is better suited for environment than previous generation
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The parts of Darwin’s theory
• 1. Overproduction• 2. Variation of individuals• 3. Differential reproductive success
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1. Overproduction
• Living things tend to produce more offspring than are able to survive
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2. Individual Variation
• Individuals in a species are different from each other
• Some are better adapted to their environment than others
• Where does the variation ultimately come from?
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Mutations are the source of all genetic variaton
• Mutations- Changes in DNA of an organism
• Mutations can be caused by mutagens
• UV radiation, toxins, etc.• Also come from errors in
DNA replication• Also from errors in
crossing over• And meiosis, etc.
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3. Differential Reproductive Success
• Those that are better adapted to their environment are more likely to survive
• Those that survive will pass their genes to their offspring
• Populations evolve, not individuals
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As a result, populations
change • Population is better
adapted for survival in its environment
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In this way, the population changes- microevolution
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When populations of a species become isolated, they evolve independently, causing speciation
• The isthmus of Panama only formed ~3mya
• Its formation isolated shrimp species into Caribbean and Pacific populations
• Now they are separate species
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Given more time, microevolution results
in macroevolution
• Many speciation events over many millions of years leads to great changes
• Fossils from Pakistan and India have elucidated the evolution of the whale
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By this principle, all life evolved from a common ancestor
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More recently, humans and apes evolved from a common ancestor
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Primarily because of this, many people didn’t like Darwin’s theory
• One consequence of the theory is that all living things have a common ancestor
• Humans did not descend from chimpanzees- but they do share a common ancestor
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Consequences of Natural Selection
• Some insects can tolerate pesticide
• Survivors pass resistance genes to the next generation
• Do these genes exist before the crops are sprayed?
• What other examples are there of this?
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What can be said about these insects?
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Consequences of Natural Selection
• Some insects can tolerate pesticide
• Survivors pass resistance genes to the next generation
• Do these genes exist before the crops are sprayed?
• What other examples are there of this?
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Evidence for evolution
• Fossil evidence• Biogeography• Comparative anatomy • Comparative embryology• Molecular biology
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Which of the following is a orrectly written scientific name?
• A) Australopithecus afarensis • B) homo sapiens • C) musca domesticus • D) Acer pennsylvanicus
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Layers of sediment fall upon dead organisms, ultimately forming fossils,
creating the fossil record
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Looking down layers is looking back in time
• The principle of superposition
• The layers of the grand canyon go back over 600 million years
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Fossil Evidence shows variant species in different layers
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Which of these creatures would be least likely to be successfully fossilized?
• A) Turtle • B) Rose flower • C) Rhinoceros • D) Clam
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Biogeography
• Marsupials are not better adapted to Australia
• Invasive placental mammals are driving many marsupials to extinction
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Comparative anatomy
• Similar structures exist in dissimilar animals, serving dissimilar functions
• Homologous structures suggest a common ancestry
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Vestigial Structures suggest terrestrial ancestry in whales
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Comparative embryology
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Evidence from Molecular Biology
• Similar animals have similar DNA sequences
• Less similarity of species= less similarity of DNA
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Other ways a population can evolve without natural selection
Genetic DriftThe bottleneck effect
The founder effect
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Genetic Drift- the change in allele frequencies in a population or species over time by chance
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Figure 13.23
Population bottlenecks magnify the effects of luck
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Consequences of a bottleneck
• Cheetahs have very low genetic variation
• How can a bottleneck reduce diversity in a population?
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A population retains the genes of its founder(s)
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Special kinds of selection
• Sexual selection• Artificial selection
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Sexual Selection• Competition within sexes
is a major source of differential reproductive success
• Males compete, or females select
• Sexual selection leads to sexual dimorphism
• “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick”- Charles Darwin
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Pair bonding is greater in species which are less dimorphic
• What about humans?• Are humans a
tournament species, or are a pair-bonding species?
• How can you tell?
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Artificial selection shows the pliancy of species morphology
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Human Evolution
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Humans have several adaptations which distinguish us from relatives
• Pelvis for bipedal walking
• Opposable thumbs, but not toes
• Larger braincase
• Humans did NOT evolve from chimps- but the share a common ancestor
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Scarcity of fossils makes tracing human history difficult
• Hominin fossils are numbered in the dozens
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Humans have their roots in Africa
• Primates evolved in• While evidence of
Hominin ancestors can be found in Asia, true modern humans are believed to have come from Africa ~200-100kya, with migrations beginning ~60kya
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Homo neanderthalis is thought to be an extinct subspecies
• Found primarily in Europe• Arrived in Europe ~350kya,
extinct by ~30kya• Adapted for cold• Wiped out by H. sapiens?• Did they crossbreed with
modern H. sapiens?• mtDNA evidence suggests
they did not
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Which of the following refers to the ability of early hominids to
walk on two feet?• A) Bipedalism • B) Digitigrade • C) Plantigrade • D) Tetrapedal