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Chapters 14, 15, and 16
Evolution
Evolution
The definition of Evolution is:
Change over time.
Biological Evolution is:
Change in allele frequency in
population over time
Process by which modern organisms
have descended from ancient
organisms (slow change over long
time)
• Even relatively quick evolution takes
hundreds of thousands of years.
Age of the Earth
We now know Earth is approximately 4.5
billion years old.
Activity Time: Organize the strips of
matter chronologically from oldest to
most recent.
The evolution model includes the scientific evidence
and the related inferences suggesting that:
I. The universe and the solar system emerged by naturalistic
processes.
II. Life emerged from nonlife by naturalistic processes.
III. All present kinds emerged from simpler earlier kinds, so that
single-celled organisms evolved into invertebrates, then
vertebrates, then amphibians, then reptiles, then mammals, then
primates, including man.
IV. Mutation and natural selection have brought about the
emergence of present complex kinds from a simple primordial
organism.
V. Man and apes emerged from a common ancestor.
VI. The earth's geologic features were fashioned largely by slow,
gradual processes, with infrequent catastrophic events restricted to
a local scale (uniformitarianism).
VII. The inception of the earth and then of life must have occurred
several billion years ago.
James Hutton
In the late 1700’s, James Hutton (a
geologist) proposed that rocks,
mountains, and valleys have been
changed by water, wind, temperature,
volcanoes, and other natural forces.
He theorized that Earth was much older
than a few thousand years, which didn’t
set well in the traditional timeframe of
Creationism.
Geologists
Charles Lyell (early 1800’s) – agreed
with Hutton and said that scientists must
always explain past events in terms of
observable, PRESENT events and
processes (uniformitarianism).
Darwin used the work of Hutton and Lyell
as a basis for his theories of slow change
over time. Darwin’s work was a
biological duplicate of Hutton and Lyell’s
works in geology.
Geologists study Earth’s rocks
Fossils are preserved remains of
ancient organisms
Found in Sedimentary rock: layers
of sand, silt, and clay in streams,
lakes, rivers, and seas form rock
that may have trapped living
organisms
Fossils can be direct evidence (ex.
Bones, hair, feathers) or indirect
evidence (ex. Molds, footprints)
Fossil Hominid Skulls
Fossil Evidence
Fossil record – Shows change over
time. Some timeframes are
missing, but will show change of
climate and geography.
Ex: Shark teeth in Utah
• How can this be?
Geologists study Earth’s rocks
As fossils are found that don’t resemble
organisms today, evidence increases
that Earth has changed and that
organisms have changed with it.
Biologists and geologists date Earth’s
past with the help of rocks.
Geological Time Scale
RELATIVE DATING
Technique used to determine age
of fossils relative to other fossils in
different layers of rock. This
technique is VERY approximate.
Geological Time Scale
ABSOLUTE (RADIOACTIVE) DATING
Using radioactive elements in rock
that decay at a steady rate to
determine age. Decay measured in
terms of HALF-LIFE.
Radioactive Decay
During radioactive decay, the
atoms of one element break down
to form something else.
Lose a
proton
6 protons
4 neutrons
5 protons
4 neutrons
Rocks contain radioactive elements, each
having a different half-life.
Half-life – time required for half the
radioactive atoms in a sample to decay
End of half life  half of remaining
atoms have decayed
EXAMPLES:
Uranium-238  Lead-206
HL = 4.5 B yrs
Potassium-40  Argon-40 HL = 1.3 B yrs
Carbon-14  Nitrogen-14 HL = 5770 yrs
Scientists often date rocks using
Potassium-40. This element decays to
form the stable element Argon-40.
It has a half life of 1.3 billion years
This is used in the oldest rocks on
earth.
K-40
Formed
K-40 Ar-40
Ar-40
1.3 billion
2.6 billion
Uranium and Potassium are useful for
dating rocks
Carbon-14 is useful for dating things
that were once alive such as wood,
natural fiber, or cloth
C-14 is in the atmosphere; living
things take it in their cells. After the
organism dies, it doesn’t take in any
more C-14. We can then compare
the amounts of C-14 to N-14,
knowing its half-life, to determine the
age of the sample
PRACTICE
1. 20 g C → 10 g C → 5 g C
How long did this take?
2. What happened to the other 15 g
of C?
3. 3.9 Billion years have passed and
there is only 10 g of Potassium
left. What was the original
amount before radioactive decay
started happening?
Jean Baptiste de Lamarck
(1744-1829)
He also recognized that organisms were
adapted to their environments and that
they change
He relied on three ideas:
1. A desire to change (innate drive for
perfection)
2. Use and disuse (Giraffe’s necks and
vestigial organs)
3. Inheritance of acquired characteristics
Darwin’s Dilemma
Set sail around the world in 1831 on
HMS Beagle on a 5 year voyage
He had prior knowledge of geology
(Lyell was a good friend) and
agriculture that helped influence the
development of his theory
Anchored all along the way
and took samples from
each place
Voyage of the Beagle
Darwin’s Dilemma
He collected and studied beetles from
Brazil, birds from Chile, and iguanas,
tortoises, and finches from the
Galápagos Islands
He noticed similarities between
mainland (Ecuador) and Galapagos
finches
Later, he noticed differences in beak
size among finches from different
islands in the Galapagos
Darwin’s Dilemma
Thomas Malthus – wrote paper on
population growth in Great Britain
Population grows exponentially
Limiting factors on growth (carrying
capacity)
• Food
• Area
• Resources
Darwin’s Dilemma
Darwin applied Malthus’, Hutton’s, and
Lyell’s work to species’ ability to change,
and called the mechanism Natural
Selection
Nat.Sel.: Process by which organisms
with favorable variations survive and
produce more offspring than less welladapted organisms
He was sure Nat.Sel. was true,
but he feared public ridicule. So,
he kept his ideas to himself
Darwin’s Dilemma
Alfred Russel Wallace (1823-1913),
working independently, came to the
same conclusions as Darwin
He sent a manuscript to Darwin,
basically for proofreading
“I never saw a more striking coincidence…
so all my originality, whatever it may amount
to, will be smashed.” – Charles Darwin
Letter to Charles Lyell, June 18, 1858
Darwin quickly abridged and published his
work “On the Origin of Species”
Evidence in Living Organisms
Comparative embryology:
These anatomical similarities indicate
similar genetics are at work
Become more dissimilar as they grow
• Cell specialization and differentiation
Common ancestor?
Ernst Haeckel “fudged” his data
• Big no-no; hurt evolutionary theory
for a long time
Evidence in Living Organisms
Evidence in Living Organisms
Comparative anatomy:
Homologous Structures –
structures that are similar in
anatomy, but may serve very
different functions.
• Ex: cat, whale, and human
forearm
Homologous Structures
Flying
Swimming Running Grasping
Evidence in Living Organisms
Comparative Anatomy (cont.):
Analogous Structures – structures that
serve similar functions, but have evolved
independently of each other
Not homologous;
analogous
Not homologous;
not analogous
Homologous;
not analogous
Homologous;
analogous
Evidence in Living Organisms.
Comparative Anatomy (cont.):
Vestigial organs – organs that have little
or no purpose in the organism; may
become smaller or even disappear
• Ex: Tailbone or appendix
in humans
• Ex: Tiny leg bones in
snakes (boas and
pythons) thought to come
from 4 legged ancestor
Evidence in Living Organisms
Comparative biochemistry and
molecular biology:
All cells have DNA, RNA,
ribosomes, the same 20 amino
acids and use ATP as an energy
carrier.
Similarities in chemical compounds
such as DNA and RNA
Evidence in Living Organisms
Cytochrome c
is a highly
conserved
respiratory
protein
containing 104
amino acids in
humans
What Homologies tell us…
Similarities in structure and chemistry
provide powerful evidence that all
living things evolved from a common
ancestor
Darwin Concluded:
Living organisms evolved through
gradual modifications of earlier forms
 descent with modification
What Similarities tell us…
Two types of evolution can account for
homologous AND analogous structures
Divergent evolution
Convergent evolution
What Similarities tell us…
1. Divergent evolution – two species
evolve from a common ancestor
(speciation)
They share similarities in anatomy,
biochemistry, and embryology due to
common ancestry
Explains homologous structures
What Similarities tell us…
2. Convergent – two species apparently
becoming more similar
Two species have adapted in similar
ways to similar environmental
conditions
NOT due to common ancestry
Explains analogous structures
Convergent Evolution
Ocotillo from California and allauidi
from Madagascar have evolved similar
mechanisms for protecting themselves
Diversity of Life
Fitness:
Physical traits and behaviors that
enable organisms to survive and
reproduce in their environment arises
from adaptation.
Adaptation allows species to be better
suited to their environment and therefore
can survive and reproduce.
4 Driving Forces behind Evol.
1. Mutation
Any change in the original DNA
ONLY source of variation in a
population!!
2. Gene Flow
Movement of genes either in or
out of a population
Migration – Immigration and
Emigration
4 Driving Forces behind Evol.
3. Genetic Drift
Change in the allele frequency in a
population by chance alone.
• Bottleneck Effect
• Founder Effect
4 Driving Forces behind Evol.
3. Genetic Drift
Bottleneck Effect:
population
undergoes a high
mortality rate;
genetic variation
decreases
dramatically
Ex: Cheetahs
Genetic Drift: Bottleneck Effect
4 Driving Forces behind Evol.
3. Genetic Drift
Founder Effect:
few individuals
leave a large
population to start
their own; gene
pool is very
limited
Ex: polydactyly in
PA Amish
Genetic Drift: Founder Effect
Genetic Drift: Founder Effect
4 Driving Forces behind Evol.
4. Selection
Natural – differential success in the
reproduction of different phenotypes
resulting from the interaction of
organisms with their environment
• Nature does the selecting
4 Driving Forces behind Evol.
4. Selection
(Natural)
Resistance –
overuse of
insecticides
and antibiotics
have bred
resistant
species of
bugs and
germs
4 Driving Forces behind Evol.
4. Selection
Artificial – breeding of domesticated
plants and animals
• Humans intentionally
do the selecting
• Cabbage, cauliflower,
Brussels sprouts, kale,
kohlrabi and broccoli have
a common ancestor in one
species of wild mustard
4 Driving Forces behind Evol.
Problems with artificial selection – not
enough genetic variation
4 Driving Forces behind Evol.
4. Selection (Sexual)
Intrasexual selection – selection
within the same sex (competition,
usually between males
 Competition, usually between
males
 Exaggerated
anatomy
Bighorn Sheep
Rocky
Mountain
Elk
Five-horned
Rhinoceros Beetles
Stagbeetles
4 Driving Forces behind Evol.
4. Selection (Sexual)
Intersexual selection – one sex
selects mate based on phenotypes
Exaggerated anatomy
Evolutionary Time Scales
Evolution can take a long time or can
occur relatively quickly
Gradualism
Punctuated Equilibrium
Evolutionary Time Scales
Gradualism – big
evolutionary
changes are the
result of many
small ones over a
long period of
time
Evolutionary Time Scales
Punctuated
Equilibrium –
speciation occurs
fairly rapidly then
remain constant
Selection can influence populations in
three major ways:
Directional Sel.
Stabilizing Sel.
Disruptive (diversifying) Sel.
Directional Selection
Environment selects
against one phenotypic
extreme, allowing the
other to become more
prevalent
Disruptive Selection
Environment selects
against intermediate
phenotype, allowing
both extremes to
become more prevalent
Stabilizing Selection
Environment selects
against two extreme
phenotypes, allowing
the intermediates to
become more prevalent
Key Points
1. Natural selection does not cause genetic
changes in individuals.
2. Natural selection acts on individuals;
evolution occurs in populations.
3. Evolution is a change in the allele
frequencies of a population, owing to
unequal success at reproduction among
organisms bearing different alleles.
4. Evolutionary changes are not “good” nor
“progressive” in any absolute sense.
Evolutionary Theory
Foundation on which the rest of the
biological science is built. Collection of
carefully reasoned and tested
hypotheses about how evolutionary
change occurs.