Transcript Ch. 4 Evolution - gettingbuggywithit

Evolution
Biology 20
Classification of Organisms
• Taxonomy – classification of organisms
• Approximately, 10 million species on the
planet, 2 million classified.
• Carl Linnaeus – 1707-1778 Developed a
naming system called Binomial
nomenclature (Genus-Species)
– Ex. Homo Sapiens
Order of Classification
Six-Kingdom Systems of
Classification
Monera
Monera
Phylogeny
Evidence of Evolution
• Evolution: all changes that have occurred in
living things since the beginning of life.
• If history of Earth is condensed to one 24hour day:
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Earth is formed at the beginning of midnight
Prokaryotes appear about 5:00 in the morning
Eukaryotes present at 4:00pm in the afternoon
Invasion of land starts about 10:00pm at night
Humans appear 30 seconds before midnight at
the end of the day
Fossil Evidence
• Fossils are remains, traces or other direct evidence
of past life forms
• Most fossils form from the burial of plants and
animals in the sediment
• Most fossils are embedded in sedimentary rock
• Paleontologists study the fossil record based on the
boundaries between the strata, this helps determine
the relative age of fossils
• Fossil links combined with modern comparative
anatomy allows us to deduce vertebrate descent:
– Fish  amphibians  reptiles  birds and mammals
Evolution of the Modern Horse
One of the few animals for which we have a fairly
complete evolutionary record is the horse, as all
the main stages of horse evolution have been
preserved in fossil form. Over 60 million years
the horse evolved from a dog-sized rainforestdwelling creature, into an animal adapted to
plains-dwelling and standing up to 2 metres high.
In the process it traded-in its multi-toed feet,
adapted for walking across the forest floor, for
single-toed hooves, suited for running over open
country.
Geological Time Scale
• Geological history of Earth is divided
into eras and periods
• Fossil record provided relative dating
of rock layers; top layer of rocks are
younger than lower layers of rock
• Absolute dating methods uses
radioactive isotopes
– Isotopes each have particular half-life or
time it takes for half of the isotopes to
decay and become non-radioactive
– Carbon 14 is used to date organic
matter; half decays to nitrogen 14 each
5730 year; limited to about last 50,000
years.
Mass Extinctions
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Extinction is death of all members of a species in wild; mass extinctions
are extinctions of many species in a short time.
Five mass extinctions in the fossil record
Following extinctions, remaining groups expand to fill habitats vacated
by extinct species
Proposed that most mass extinctions are caused by asteroid impact
– Impact of the asteroid would create climate similar to a nuclear winter with
worldwide cooling (ice age)
– Cretaceous-Tertiary(64-1.8 million years ago) border has a higher level of
iridium, rare in the Earth’s crust but common in meteorites
– Huge meteorite crater of correct age ground in Caribbean Ocean and
Yucatan peninsula; suspected sight of impact of meteor that results in
dinosaur extinction
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Marine animals fossil record indicates mass extinction occurs every 26
millions year; corresponds to movements of solar system within the
Milky Way galaxy.
Craters
Biogeographical Evidence
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Biogeography is the study of distribution of plants and animals
throughout the world
Current distribution of organisms reflects the evolutionary history,
organisms evolve in one location and spread out into other regions; for
example, no rabbits are found in South America – they originated
elsewhere and did not reach South America
Physical factors, including locations of continents, limit population
ranges
Continental drift states that continents have slowly moved over time
– Explains close puzzle-piece fit of east coast of South America with west coast
of Africa, and other continent edges
– Explains distribution of seed ferns throughout southern continents
– Explains distribution of early reptiles across many continents from time
when land was joined
– Explains divided distribution of mammals that evolved after continents
parted.
Movement of the Continents
Anatomical Evidence
• Many organisms share a unity of plan, for example, the
vertebrate forelimbs contain same sets of bones used for
different functions in bat wings, whale fins, etc
• Simplest explanation in having a common ancestor whose
basic forelimb plan was modified in succeeding groups as
each continued along it own evolutionary pathway.
• Homologous structures are similar in structure derived
through descent from a common ancestor
• Analogous structures have similar functions but differ in
anatomy and did not derive from the same ancestral
structure; for instance, an insect wing and a bird wing
Homologous and Analogous
Structures
Embryological Development
• Theory of Recapitulation
– “ontogeny recapitulates phylogeny”
– “life history repeats evolutionary history”
• All vertebrates have a tail, notochord and
pharyngeal pouches during development
• In humans
– The notochord develops into the vertebral column
– The tail becomes the sacral vertebrae (tailbone)
– The pharyngeal pouches become the Eustachian tubes,
middle ear and thyroid gland
• Simplest explanation is that the notochord and
pouches are primitive fish features and fish are
ancestral to other vertebrates
Comparative Embryology
Biochemical Evidence
• Almost all living organisms use the same basic
biochemical: DNA, ATP, many identical enzymes,
DNA triplet codes and 20 amino acids
• Similarity of biochemistry is explained by descent
from a common ancestor
• DNA base sequences differences is DNA between a
number of organisms shows less difference the
more closely related they are; for example, 2.5%
difference between humans and chimpanzees but
42% difference between humans and lemurs.
Contributors to the Theory of
Evolution
• Linneaus
– Developed the classification system (binomial nomenclature)
– Linneaus did not believe in evolution, but his classification system
helped to organize many organisms to show similar ancestry
• Buffon
– Anticipated many of Darwin’s ideas
– Extreme conflict with the church
• Larmark
– Recorded the first theory of evolution
– Two major disputable points:
• Nature has an innate tendency to evolve in the direction of increasing
complexity, determined by the interaction with environment
• Acquired characteristics will be passed onto offspring (not genetically
acquired)
Other Contributors to the Theory of
Evolution
• Cuvier
– Founder of paleontology
– Also did not believe in evolution, but did lay the ground work for
Darwin’s theory
• Hutton
– Geologist
– Proposed the Earth is always changing and is very old
• Charles Darwin
– Studied medicine and theology
– At 22 became a naturalist on the HMS Beagle which sailed through
the Galapagos Islands
– Proposed the Theory of Natural Selection
• Alfred Wallace
– Proposed the same idea as Darwim
Theory of Natural Selection
• Natural selection is a theory that proposes
that individuals whose genetic variation best
adapt them to their environments will be
most likely to survive and pass on those
traits.
Darwin’s Discovery of the Theory of
Natural Selection
(Fact 1) There is a potentially exponential increases
in population  Overpopulation
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(Fact 2) Population sizes are relatively stable
(observation)
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(Fact 3) Resources are limited
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(Inference 1) There is a struggle for existence
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Darwin’s Discovery of the
Theory of Natural Selection
(Fact 4) Individuals are unique (observation) 
Variation
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(Fact 5) Many characteristics are inherited
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(Inference 2) There is a differential survival, that is
natural selection Survival of the Fittest
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(Fact 6) The Earth is very old
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(Inference 3) Through many generations species
evolve  Origin of species by inheritance of
successful variation
Key Points of Natural Selection
• Individual differences are essential for evolution
• The struggle in nature that is of greatest consequence to
evolution is not that between different species; rather, it
is the competition within a population of a single species
to obtain food, attract a mate, escape predators, etc.
• Only the difference that are inherited are relevant to
evolution
• Evolution generally takes a great deal of time and is
ongoing.
Sources of Variation
• Mutation create the variation necessary for
Natural Selection
– Mutations are random changes in the DNA
sequence in a chromosome
– Caused by environmental factors (chemical,
radiation or viruses) or in errors when the cell
makes copies of the DNA
– Only the mutation to the chromosomes in the sex
cells are passed to the next generation.
– Mutations can be harmful, neutral or beneficial.
(most are harmful or neutral)
Sexual Reproduction and
Variability
• Asexual Reproduction = no variation
• Sexual Reproduction = variation
– In sexual reproduction there are two parents and
the offspring inherit a copy of each gene from
each parent
– The chromosomes are assorted randomly. So
each sex cell has a different combination of
chromosomes.
– Sexually reproducing species choose different
mates.
Speciation
• Species – a group of organisms that look alike
and can interbreed under natural conditions to
produce fertile offspring.
• Speciation – the creation of a new species
• Allopatric Speciation – speciation by geographic
then reproductive isolation.
Geographical Isolation
– Species become geographically isolated by some
physical barrier. A mutation occurs in one
group that does not occur in the other.
– Natural selection takes place and the populations
evolve independently.
– In time, the changes that occur between the
species are so pronounced that if the were
reunited they can no longer mate.