Download xCh 13 evolution Sp11

Darwin observed organisms in
diverse environments
Evolution and Diversity
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Ch 13
How populations evolve
Darwin observed how
organisms adapted to
their environments
The animals living on the
Galápagos Islands were
unique
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Descent with Modification
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Snail fossil
Descent with Modification
Darwin found marine fossils
on mountaintops in the Andes
observed the amazing
diversity of plants and animals
His observations lead him to
believe that organisms
change over time, or evolve
This evolutionary tree of
the elephant family is
based mainly on fossil
evidence
Charles Darwin wrote
The Origin of Species
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but resembled those in
South America.
Darwin’s theory:
Evolution by natural selection
Darwin established the ideas
of evolution and natural
selection in 1859
He proposed that:
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Modern species descended
from ancestral species
“descent with modification”
Natural selection is the
mechanism of evolution
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“Survival of the fittest”
Individuals best suited for their environment are
more likely to survive and reproduce
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Natural selection results in
adaptation to the environment
Natural selection
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The basic idea:
Organisms can change over
generations.
 Individuals with certain inherited traits
leave more offspring than others.
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Camouflage – an example
of evolutionary adaptation
Darwin’s Theory of Natural
Selection
Natural Selection
Long narrow
beak for
holding tools
Large beak
specialized for
cracking seeds
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Observation 1:
Overproduction of
offspring
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Small beak for
catching insects
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Darwin’s finches are an excellent example of
natural selection and adaptive evolution.
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Cloud of spores exploding
from a puffball fungus
Galapagos finches have beaks adapted for
specific diets
Darwin’s Theory of Natural
Selection
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All species tend to
produce more offspring
than the environment
can support.
This leads to a struggle
for existence.
Observation 2:
Individual variation
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Darwin’s insight
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Differential reproductive success
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Variation exists
among individuals in
a population.
Much of this variation
is heritable.
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Those individuals with traits best suited for
the local environment leave more offspring.
This, of course, is natural
selection
Asian lady beetles
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The Evidence for Evolution
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Fossil record
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the most direct evidence
Many fossils link ancestral and living species
Comparative anatomy
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The Fossil Record
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Similarities in structures among organisms
Closely related species have similar stages in
their embryonic development
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Molecular biology
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Fish fossil
All species share the genetic code, suggesting
that all forms of life are related
Transitional forms link past
and present
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Fossils are the preserved
remains or tracks of onceliving organisms
They are created when
organisms are buried in
sediment and their bones
become mineralized
You can tell how old the
fossils are by the layer of
rocks where the fossils are
found.
Comparative anatomy
Did whales evolve from
land-dwelling ancestors?
A series of fossilized whales
connect them to four-legged
ancestors
This is a picture of fossilized
leg bones of Basilosaurus,
an ancient whale
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Homologous structures
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The forelimbs of all
mammals are
constructed from the
same skeletal elements
Anatomical evidence of
descent with
modification
Homology among vertebrate limbs
– the same basic bones are present
in each forelimb
Comparative Embryology
Molecular Biology
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Evolutionary relationships
are determined by
comparing
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Comparative embryology is the comparison of
structures that appear during the development of
different organisms.
All vertebrate embryos share a basic set of
developmental stages
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Genomes
Genes
Proteins
Organisms that are more
distantly related show
more differences in their
DNA
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Molecular biology:
Comparing protein structure
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Molecular biology:
A ‘new’ tree of life based on rRNA
Comparison of the
amino acid sequence of
hemoglobin in different
vertebrates
The greater the number
of differences in the
amino acids in
hemoglobin, the greater
the evolutionary
distance from humans
Molecular biology is being used to understand the relationships
among different groups of organisms
Ribosomes are found in nearly all organisms
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How do organisms evolve?
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4 mechanisms of evolution
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Variation in Populations
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Mutations
Natural selection
Genetic drift
Gene flow
These forces act on populations to change
their DNA
*a population is a group of individuals of the same
species living in the same area
Mechanisms of evolution
#1 Mutation
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Mutations –changes in DNA– are
the source of genetic variation
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Create variation in a population
Can be inherited IF they are in a
germ-line cell
Mutations can take many forms
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Deletion, duplication or translocation
of blocks of DNA
Changes in a single nucleotide (or
base)
RNA sequence data is used to compare rRNA among species
Starting material: variation
in populations of plants
and animals
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Not all of this variation is
genetic and can be
inherited.
Only the genetic
component of variation is
relevant to natural
selection.
Polymorphism in garter snakes
These 4 snakes belong to the same species
Mutations
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Mutations are random
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Mutations can be beneficial, neutral, or
harmful for the organism
Not all mutations matter to evolution
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Mutations that occur in somatic cells won’t
be passed onto offspring
Only mutations that occur in reproductive
cells (eggs and sperm) matter
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Mechanisms of evolution:
#2 Natural Selection
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Natural selection occurs when some
individuals leave more offspring than
others
Of all mechanisms of evolution, only
natural selection leads to adaptation.
Natural selection: a closer look
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It’s not always “survival
of the fittest”
Reproductive success
is generally more subtle
For example, some
plants attract more
pollinators
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Mechanisms of evolution
#3 Genetic drift
Natural Selection
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More successful in
reproducing
Certain moths survive and
produce more offspring
because they are better
camouflaged
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Genetic drift – a change in the gene pool of a small
population due to chance
Example: small wildflower population
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Generation 1: only 5 plants produce fertile offspring
Generation 2: only 2 plants leave offspring
Generation 3: only plants with red flowers remain
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Two forms of the peppered moth
Genetic drift:
the bottleneck effect
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Disasters (floods,
fires, etc) kill large
numbers of individuals
Results in a drastic
reduction in
population size.
Reduces genetic
variation
 Due to chance
The white allele has been lost from the population
Genetic Drift and Hereditary
Disorders in Human Populations
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The Founder Effect
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When a few individuals
colonize a new place
Gene pool differs from
the parent population
Explains the relatively
high frequency of
inherited disorders in
human populations
established by small
numbers of colonists
Residents of an isolated island in the
Atlantic Ocean have a high rate of
hereditary blindness
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Mechanisms of evolution:
#4 Gene flow
Movement of
individuals between
populations –
migration
Introduces new
genes
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Gene Flow
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Gene flow – genetic
exchange with another
population
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Here the genes for
brown beetles become
more frequent in the
green beetle population
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Tends to reduce genetic
differences between
populations.
The migration of people
throughout the world increases
gene flow and introduces new
alleles
An important agent of
evolutionary change
Computer-generated image blending
features from several races
Evolution by natural selection
Another type of selection
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Artificial selection –
farmers breed domestic
animals and plants for
certain traits
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Individuals best suited for their environment are
more likely to survive and reproduce
Size, speed, milk
production
Examples: race horses,
dairy cows, corn, wheat,
etc etc
Sexual selection
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Sexual selection –
choosing a mate based
on physical
characteristics
A type of nonrandom
mating – individuals
choose their mates
based on certain traits
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Evolution DVD
Vol 3 Why Sex? The peacock’s
tail (5 min)
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