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Chapter 17 and 18: Darwin’s
Theory of Evolution
Source: http://anthro.palomar.edu/evolve/evolve_2.htm
Theory of Evolution
Evolution:
A gradual process (over millions of years!)
by which modern organisms have
descended from ancient ancestors
Evolution is based on scientific facts,
observations and hypotheses
Proposed by Charles Darwin… let’s
examine his voyage and data.
Charles Darwin
English naturalist
Set sail on a 5 year cruise on the HMS
Beagle in 1831
Source: http://anthro.palomar.edu/evolve/evolve_2.htm
The Voyage
At each stop, Darwin:
Made biological and geological
observations
Collect plant and animal specimens
Collected Fossils
Darwin Observed
Biodiversity – diversity of life
Vast number of species
Each well adapt to its environment
An intriguing geographic distribution of species
Estimates calculate there are 10 million
species today.
This number only represents 1% of all
species that ever lived on Earth!
The Galapagos Islands:
An Important Influence on Darwin
Small group of Islands located 1000km west of South
America
The Islands had very different climates
Darwin noticed that plants and animals varied noticeably
from island to island.
 Land Tortoises
Source: www.thebestofecuador.com
Darwin found the shell shape
corresponds to the habitat
Lonesome George
Figure 15-3 Variations in Shell Shape (p. 371)
Darwin’s Thoughts
Where did all
the animals
come from?
Where did
humans
come
from?
What
about
fossils?
Has
everything
always been
here?
How old
is the
earth?
Do plants
ever
change?
What
happened
to all the
dinosaurs?
Lab Requirements: typed, stapled
1.
2.
3.
4.
Hypothesis (if/then)
Procedures (#’d, clear, step by step)
Data (clean table – ok if by hand)
Analysis (calculations? summary sentences?
graph w/labels + title – also ok by hand)
5. Conclusion (follow requirements in ppt)
Altogether about 35 points
Use weebly documents to guide you!
Darwin’s Proof
Evidence of Evolution
The Fossil Record
Geographical Distribution
Similarities
• Embryology
• Chemical Compounds
• Body Structures
Evidence in support of evolution:
Fossil record
Geologic time scale
Geographic distribution of species
Embryology
Anatomy (“body structure comparisons”)
Chemical comparisons (DNA/RNA, Protein)
The Fossil Record
By comparing older fossils with younger
fossils, evidence of change is clear.
Geologic Time Scale
The age of Earth provides evidence that time
was available for evolution of species
Precambrian 4.6 bya-544 mya
Paleozoic 543-245 mya (cambrian explosion)
Mesozoic 245-67 mya
Cenozoic 66 mya to present
Radiometric vs. Relative Dating
½ Life of Elements
Decay
Depths
of Strata
Geographic Distribution of
Living Species
Darwin discovered the existence of
similar but unrelated species in different
locations
Darwin later realized the similar animals
were products of different lines of
evolutionary descent.
Similarities in Early
Development
Early1900’s: embryos thought to look the
same
Current knowledge:
• Common genes play a role in early
development
• Later stages show differences in embryos
• Differences are from genes that have changed
due to evolution
Similarities in Early Development
Similarities in Body Structure
Evolutionary change alters structure and appearance
based on their FUNCTION
Why? Structures that allow organisms to survive in
their environment increases fitness
Homologous Structures:
• Limbs or body parts that resemble one another in
structure
-However, these may
offer different functions
-They suggest common
ancestry of organisms
That experienced divergent
evolution
Analagous Structures
Similar
function, but
highly unique
structure
Vestigial Organs
Organs that have no or little purpose.
Evolution has lead to adaptations that suit
particular organisms
Similarities in Chemical
Compounds
All organisms use DNA and/or RNA
Many organisms have similar proteins
The more closely related two species
are, the more their chemical properties
resemble each other.
Evidence for Evolution Ticket Out
1. Name at least four forms of evidence in
support of the theory of evolution.
Challenge: name ALL 6 discussed!
2. Why are structures like our tailbone,
wisdom teeth and the appendix evidence
that evolution has occurred?
Darwin Presents His Case
Darwin reflected on his findings for
many years after returning home.
He wrote about his theories in, On the
Origin of Species.
Published in 1859
23 years after the voyage of the Beagle
http://www.pbs.org/wgbh/evolution/educators/teachstud
s/svideos.html
Inherited Variation vs.
Artificial Selection
Variations:
Different forms or ‘alleles’ for a trait
Inherited Variations
Traits passed on from parent to offspring
Artificial Selection (ex. dog breeding)
Humans select useful variations from naturally
occurring traits
Selective breeding practices
Evolution by Natural
Selection
The Struggle for Existence
Darwin thought nature used an “artificial selection
process”
Members of each species compete for resources
Natural Selection (hummingbird video?)
Processes in nature that over time results in only
the survival of the fittest species
Results in changes of inheritable characteristics of
a population.
Changes increase a species’ fitness in its
environment
Survival of the Fittest
Fitness
Ability of an individual to survive and
reproduce.
Fitness is a result of adaptations
Adaptation
Physical and behavioral traits that allow an
organism to survive in its environment
Darwin Concluded:
Over long periods of time, natural selection
produces organisms that have different
Structures
Niches
Habitats
Species descended with modifications from a
common ancestor.
Implies all living things are related to one another
This principle is known as common descent
Darwin’s Finches
Similarities can be explained
with Darwin’s theory:
Living organisms evolved with gradual
modification of earlier forms of an
ancestor with common descent.
Let’s Look at an Example…
In pre-industrial England, there was a
species of moth called the
Peppered Moth (Biston betularia)
Almost all peppered moths were gray with
dark flecks
Rarely were they black
The Peppered Moth
The peppered moth tend to rest
on tree trunks during the day
The gray moth were well
camouflaged on the gray tree
trunks
Black moths stand out and are
easy targets for birds.
The Peppered Moth
Now, turn to England
during Industrial Times…
Pollution from the factories
turned tree trunks black
with soot.
Now, the black moths were
camouflaged on the trees.
The Peppered Moth
The black moths had a
better chance of survival
They had a higher fitness
After many moth
generations, almost all the
months in industrial areas
were black
The Peppered Moth
Black coloration is an adaptation to
an environment with black tree
trunks
In an industrial environment, black
moths survive to reproduce better
than gray moths.
Therefore, their genes are passed
on to future generations
Tix out?
Why did the peppered moth change color
over many generations in England?
2-3 sentences, use the word adaptation
AND fitness
Mechanisms of Evolution
1. Population Genetics and Evolution
2. The Evolution of Species
3. Patterns of Evolution
1. Population Genetics and
Evolution
Populations evolve, individuals don’t
Natural processes can lead to changes
in a population’s gene pool.
Gene pools
• (genotypes vs. phenotypes)
Allele frequency
Genetic equilibrium
1. Population Genetics and
Evolution
Changes in Genetic equilibrium lead to
evolution
Genetic drift (changes to allele freq. by random
chance)
Mutations
Migration
Natural disasters
1. Population Genetics and
Evolution
Natural selection acts upon variation in
populations
A. Stabilizing Selection:
• favors average individuals
B. Directional Selection:
• favors the one extreme form
C. Disruptive Selection:
• favors both extremes
2. The Evolution of Species
Speciation: The development of a new
species which can no longer interbreed or
produce fertile offspring with it's
original ancestor.
In other words: the evolution of a new
species
2. The Evolution of Species
Physical barriers can prevent interbreeding
Geographic isolation
• Prevents gene flow between populations
2. The Evolution of Species
Geographic isolation can lead to
reproductive isolation
• Inability to breed, or mating behaviors
change
• Behavioral isolation
Chromosome alternations cause speciation
Errors in chromosomes result in ‘polyploid’
organisms
2. The Evolution of Species
Speciation can
occur rapidly or
slowly
Gradualism
vs. punctuated
equilibrium
3. Patterns of Evolution
Species diversify when introduced to new
environments
Adaptive radiation
Divergent evolution
homologous structures are evidence of this
Patterns of Evolution
Distantly related species can evolve similar
features
Convergent evolution
Analogous structures
are evidence of this