Download Evolution: A History and a Process

•You will be able to describe Darwin’s theory of
natural selection as well as give examples that
support the theory.
•You will be able to describe the conditions
required for natural selection.
Recall
•Evolution: changes
that transform life over
an immense time.
•Darwin published , The
Origins of Species
making two main points
for the mechanisms of
evolution…
1. Descent with
modification
2. Natural selection
Decent with Modification
 Species living today descended from ancestral species
 Species spread into various habitats over millions of
years
 Species accumulated different modifications, or
adaptations, to diverse ways of life
 Results in diversity of species
Natural Selection
 Process by which individuals
with inherited characteristics
well-suited for their
environment leave more
offspring on average than do
other individuals
 Survival and reproduction of
the fittest
Theory of Natural Selection Flow
Chart
Population of
Organisms
Overproduction
Variation
Struggle for
existence
Differences in
reproductive success
Evolution of
adaptations
What have you learned?
 What are the two main points that Darwin made in is
book to ague the mechanisms of evolution?
 Descent with modification and natural selection
 What is natural selection?
 Process by which individuals with inherited
characteristics well-suited for their environment leave
more offspring on average than do other individuals
 Describe some conditions that could lead to a
struggle for existence among individuals in a
population.
 Over population, limited resources, changes occurring
in the environment
Your turn to model natural
selection: Toothpicka
Natural Selection in Toothpicka
 Pre- activity:
 Hypothesize what will happen to the recessive allele
after multiple generations if no new alleles enter the
population?
 Analysis:
 Do the results support your hypothesis?
 What happened to the frequency of dominant alleles
from one generation to the next?
 What happened to the frequency of recessive alleles
from one generation to the next?
 How would this likely compare and contrast to what
would typically happen in nature?
Evidence of Evolution
 The fossil record= shows patterns of evolution over
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

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millions of years
Comparative Anatomy
Comparative Embryology
Comparative Biochemistry: amino acid tables
Geographic Distribution: similar organisms separated
by land
Fossil Record
 Fossils provide
a record of
species that
lived long ago.
 Fossils show
that ancient
species share
similarities
with species
that now live
on Earth.
Comparative Anatomy
 Homologous structures= anatomically similar
structures inherited from a common ancestor
Comparative Embryology
 Similar phases of development
Comparative
Biochemistry
 Common ancestry can be seen
in the complex metabolic
molecules that many different
organisms share.
 Organisms with closely related
morphological features have
more closely related molecular
features.
Geographical
Distribution
 The distribution of
plants and animals
that Darwin saw first
suggested evolution
to Darwin.
 Patterns of migration
were critical to
Darwin when he was
developing his theory.
 Evolution is
intimately linked with
climate and
geological forces.
What have you learned?
 What are the five things that provide evidence for
evolution?
 Fossil Record
 Comparative anatomy
 Comparative embryology
 Comparative biochemistry
 Geographical Distribution
 In your foldable if you missed something update it
with the new information.
You will be able to discuss mechanisms of
evolution other than natural selection
such as genetic drift and gene flow.
Gene Pool
Consists of all the
alleles in all the
individuals that
make up a
population.
The process of
meiosis (specifically
crossing over) and
fertilization shuffle
alleles in the gene
pool giving us
genetic diversity
Genetic Drift
 A change in the population due to chance
 All populations are subject to some genetic drift;
however, the smaller the population the greater the
impact.
 Bottleneck effect- disasters can reduce the size
of a population. By chance some alleles are
represented more than others while others are
completely eliminated
 Founder effect- when a few individuals colonize
an isolated habitat. There is low genetic makeup
Demonstration for Genetic Drift
 Hypothesis:
 What would the populations look like generations
from now if there were no environmental changes
and the gene pool remained the same?
 Analysis:
 What are some deadly “chance” events?
 How did the removal of some of the marbles
(change in the gene pool) affect each population?
 How did the impact of genetic drift contrast
between the small population and the larger
population?
Gene Flow
 The exchange of genes with another population
 Occurs when fertile individuals or their gametes
migrate between populations
 Tends to reduce genetic differences between
populations
What have you learned?
 What is a gene pool?
 All of the alleles in all of the organisms that make up a
population
 What are the two main forces of evolutionary change
in gene pools other than natural selection?
 Genetic drift and gene flow
 How can genetic drift cause a substantial change in
allele frequencies in small populations?
 It can reduce genetic variations