Download Chapter 15 – Darwin`sTheory of Evolution 15

Evolution
19.1, 16.1-16.4, 17.1-17.4, 19.2
Fossils provide evidence about
extinct species
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Earth is more than 4.6 billion years old.
Relative dating - Uses index fossils to determine the
relative dates of rock layers.
Radiometric (absolute) dating – Uses the proportion of
radioactive : stable isotopes to calculate age.

Half-life – time required for half of the radioactive atoms in a sample
to decay, or break down into stable isotopes.
• Each radioactive element has a different half-life.
• This provides natural “clocks” that tick at different rates useful for dating rocks or fossils.
• carbon-14 – produced at a steady rate in the atmosphere,
decays into carbon-12 in 5730 years, used in absolute dating.
Theory of evolution
Theory – a well supported testable
explanation of phenomenon occurring in the
natural world.
 Evolution – the process by which modern
organisms changed over time from ancient
common ancestors.

Microevolution – change in allele frequency in
populations over generations.
 Macroevolution – large scale change, such as
the formation of new species.
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3 patterns of biological diversity
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Species – group of similar organisms that
can breed and produce fertile offspring.
1. Species vary globally – different yet
ecologically similar animals are found in
different yet similar environments.
 2. Species vary locally – different yet related
species occupy different habitats in one area.
 3. Species vary over time – fossils of extinct
species are similar to current species.
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Remember…
The Earth is old and the process of change
exists today.
 Traits acquired during an organism’s lifetime
are NOT passed to it’s offspring!
 Most organisms don’t survive to reproduce!
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Examples: sea turtles, insects, etc.
Artificial selection
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Artificial selection – nature provides
variation (variety) in organisms’ traits, but
humans choose to breed those organisms
that have the most useful traits.
Example: humans breed cows that produce the
most milk.
 Example: humans breed trees that create the
most fruit.
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Summary: Theory of evolution
•
•
Species are different due to variation in
their genes (variation results from random
mutation).
Some individuals are better suited for
survival, and will leave more offspring
(natural selection or survival of the fittest).
Summary: Theory of evolution
•
•
Over time, change within species leads to
the replacement of old species by new
species as less successful species
becomes extinct.
There is clear evidence from fossils,
anatomy, physiology, DNA, and
embryology that the species now on Earth
have evolved from ancestors that are now
extinct.
Natural selection

Darwin proposed a mechanism for evolution
that he called natural selection.

Individuals whose characteristics are well-suited to their
environment survive and reproduce.
• By surviving, these attributes can be passed onto their children,
causing an increase of these traits in the species population,
thus causing a gradual change in the characteristics of the
population.
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Individuals whose characteristics are not well-suited to
their environment die or leave few offspring.
Because natural selection favors a certain trait over
others, more individuals in the population carry the
genes for that trait.
AKA: survival of the fittest.
Parameters of evolution by NS
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1. Struggle for existence – more organisms are produced
than can survive.
 Competition – individuals or groups of organisms
compete for similar resources (territory, mates, food,
water, etc.) in the same environment.
2. Variation and adaptation – some variations are better
suited.
 Adaptation – heritable characteristic that increases an
organism’s ability to survive and reproduce.
3. Survival of the fittest – individuals with adaptations that
are well suited to their environment survive and reproduce.
 Fitness – measure of how well an organism
survives/reproduces.
Common descent
Common descent – all species (living and
extinct) descended from a common
ancestor.
 Over many generations, adaptations caused
a successful species to evolve into a new
species.
 The fossil record provides evidence for this
descent with modification.
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Evidence for evolution includes:
1.
2.
3.
4.
5.
6.
7.
Geographic distribution of species
Fossils
Anatomy (homologous structures)
Physiology (analogous structures)
Embryology
Universal genetic code
Biochemical homology
Geographic distribution of species
Species of animals on different continents
had similar structures and behaviors.
 Darwin theorized that animals on each
continent were living under similar
ecological conditions and were exposed to
natural selection in a similar way.
 Similar selection pressures caused
animals to evolve common features.
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Fossils

A fossil is the preserved or mineralized
remains (bone, tooth, shell) or trace of an
organism that lived long ago.
Fossils show evidence that support the ancestry
between species.
 Fossils trace the evolution of modern species
from extinct ancestors.

• Example: Fossils have shown that whales evolved
from four legged land mammals; 1990’s transitional
forms of whales found.
Anatomy
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Evolutionary relationships can be viewed by
studying and comparing anatomy.
Scientists view the anatomy of limbs and see
common similarities.
 Over course of evolution, vertebrates moved
into environments causing different survival
needs.
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Anatomy
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Homologous structures – parts of different
organisms (that are often quite dissimilar)
that developed from the same ancestral
body parts.
Forelimbs of whales, bats, crocodiles, and
chickens have similar anatomy but are
modified for different functions – common
ancestry.
 Are similar in structure but differ in function!
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Physiology
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Analogous structures -- structures that are
similar in appearance and function but have
different origins and usually different internal
structures.
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Examples: a bat’s wing and a moth’s wing-both are wings and both are used for flight, but
a bat has bones and a moth does not.
Physiology
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Vestigial structures – any body structure that
has reduced or no body function.
Examples: A human’s appendix; a whale’s pelvis.
 As species adapt to environments the change in
form and behavior and continue to inherit these
structures as part of the body even though they
have no function.
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Embryology
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Embryology shows links between different
species.
Embryos of different species in early
development are indistinguishable from each
other.
 Common cells and tissues develop in similar
patterns in all vertebrates.
 Illustrates descent from a common ancestor.
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Universal genetic code
Genetic code – mRNA codons specify
particular amino acids.
 The genetic code of all organisms on Earth
(bacteria, yeast, fruit flies, humans) is the
same!
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Example: the AUG codon always codes for the
amino acid methionine.
Biochemical homology
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Similar DNA, RNA, and amino acid
sequences amongst species in same
taxonomic group.
Remember comparing your insulin gene DNA
and amino acid sequences to that of a cow?
 Hox genes determine embryonic head-to-tail
patterning and are conserved in almost all
multicellular animals.
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Allele frequencies
Population – mating group of organisms of
the same species.
 Gene pool – all genes (and their alleles)
present in a population.
 Allele frequency - # of times allele occurs in
a population.
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Changes as population evolves over time.
 Natural selection operates on individuals, but
causes a change in the allele frequency.
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Sources of genetic variation
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The main source of genetic variations in
populations is mutations!!!!
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These mutations occur randomly.
Not all mutations affect an organism’s fitness.
Only heritable mutations matter for evolution.
Neutral mutations don’t change phenotypes.
Other sources of variation include:
1.
2.
Genetic recombination during crossing over and
independent assortment in meiosis.
Lateral gene transfer (bacteria only)
•
Bacteria swap plasmids between members of the same
generation, then pass them to their offspring.
NS and phenotype
An organism’s genotype and environmental
conditions makes up its phenotype.
 Natural selection operates on variation in
organisms’ phenotypes.
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Higher fitness = phenotypes better suited for the
environment.
Phenotypes for traits
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Number of phenotypes for a trait depends
on how many genes control the trait.
• Single-gene trait – trait
controlled by one gene.
• Ex. Banded or un-banded shell.
• NS on these traits leads to
changes in allele and pheno.
frequencies.
• Polygenic trait – trait
controlled by two or more
genes.
• Ex. Height in humans.
• NS on these traits affects
fitness of phenotypes.
NS on polygenic traits leads to
selection in populations
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When NS on polygenic traits affects the
fitness of phenotypes, it leads to selection:
1.
2.
3.
Directional selection
Stabilizing selection
Disruptive selection
Types of selection in
populations
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Directional selection –
organisms at one end of the
curve have a higher fitness
than those in the middle or at
the other end.
Stabilizing selection –
organisms in the center have
highest fitness.
Disruptive selection –
organisms at the ends of curve
have highest fitness.
NS is not the only source of
changes in allele frequencies
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Genetic drift – change in allele frequency
that occurs in small populations due to
random chance.
Genetic bottleneck – change in allele frequency
following a dramatic reduction in population
size.
 Founder effect – change in allele frequency
following migration of a small subgroup out of
the population to start a new population.
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Genetic equilibrium
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Genetic equilibrium – a MODEL to explain
what would happen to a hypothetical, nonevolving population.
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Allele frequencies NOT changing.
Hardy-Weinberg principle – states that allele
frequencies in a population should remain
constant unless something causes them to
change.
Hardy-Weinberg
P = frequency of dominant allele.
 Q = frequency of recessive allele.
 Equation: p2 + 2pq + q2 = 1 AND p + q =1
 Equation in words: (frequency of AA) +
(frequency of Aa) + (frequency of aa) =
100% AND (frequency of A) + (frequency of
a) = 100%
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Hardy-Weinberg
Remember genetic equilibrium occurs in
large populations.
 HW predicts that 5 conditions can disrupt
genetic equilibrium and cause evolution to
occur:
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5.
Nonrandom mating (sexual selection)
Small population size – leads to of genetic drift.
Migration (immigration or emmigration) – aka gene flow
into or out of a population.
Mutations ***
Natural selection – different fitness exists for different
alleles.
Macroevolution
Speciation – evolutionary process by which
new species arise.
 Extinction – the end of a species.
 When environments change, the process of
evolution enables some species to adapt to
new conditions and thrive while some
species fail to adapt and become extinct.
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Speciation
Species – population of organisms that can
interbreed.
 Speciation – evolution/formation of a new
species.
 Niche - combination of an organism’s
profession and place where it lives.
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No 2 species can occupy the same niche in the
same location for a long period of time!
 The more efficient species will survive and
reproduce driving the other to extinction.
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Isolating mechanisms of speciation
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Reproductive isolation occurs when 2 populations
can’t interbreed - causes speciation!
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Once reproductive isolation occurs, natural selection increases the
differences between the separated populations.
1. Behavioral isolation – different courtship.
2. Ecological/habitat isolation – can only mate in specific or
preferred habitats.
3. Mechanical isolation – no sperm is transferred.
4. Gametic isolation – no fertilization of egg occurs.
5. Temporal isolation – reproduce at different times.
Geographic isolation – population becomes
divided (isolated) by a physical barrier.
Rates of speciation
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Gradualism – slow, steady
change leading to new
species.
Punctuated equilibrium –
brief periods of rapid
change leads to the
formation of new species.
•
Rapid change occurs when a
small population is isolated
from the rest of the population
or migrates.
Molecular evolution
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Molecular clock – uses mutation rates in DNA to
estimate the time 2 species have been evolving
independently.
 Based on neutral mutations – those not under
selection.
Genes evolve through:
 Modification of existing genes.
 Duplication of existing genes.
• Crossing over – during meiosis.
• Gene duplications – extra copies undergo mutations.
• Gene families – multiple copies of duplicated gene
make similar yet different proteins.
Patterns of evolution
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Divergent evolution – single species or group of species
evolve over a short period of time into different forms living
in different ways due to a change in environment that
makes new resources available.
 Aka adaptive radiations
 Ex. Dinosaurs, Darwin’s finches.
Convergent evolution – similar structures are produced in
distantly related organisms.
 Ex. Mammals that feed on ants/termites evolved
independently 5 times.
Coevolution – 2 species respond to changes in each other
over time.
 Neither can survive without the other.
Summary…
1.
2.
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4.
Individual organisms differ from one
another and differences are inherited.
Organisms produce many offspring and
some do not survive.
Organisms compete for limited
resources.
Each organism is unique and has
different advantages and disadvantages
in its struggle to survive.
Summary…
5.
6.
7.
8.
Adaptations that are best suited for an
environment allow organisms to survive
and therefore reproduce.
Species change over time.
Species alive today have modifications
from ancient ancestors.
All organisms on Earth are united by
common descent.