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EVOLUTION
Descent with Modification/
Change over Time
CHANGE OVER TIME

Evolution – theory that concerns how species change
over time.
the process by which modern organisms have descended from
ancient organisms.
 change is very slow and only in minor ways
 Can individual organisms evolve? NO!!!
 Populations of organisms do evolve as a result of a change in
gene pool.



Theory – a well supported, testable explanation of
phenomena that have occurred in the natural world.
Charles Darwin –joined the crew of the HMS Beagle
and set sail for a voyage around the world. During his
travels, Darwin collected evidence that led him to
propose the theory of evolution.
DARWIN’S THEORY OF EVOLUTION

Galapagos Islands – Darwin observed that the
characteristics of many animals and plants varied
noticeably among the different islands of the
Galapagos.
LAMARCK’S EVOLUTION HYPOTHESIS


Jean-Baptiste Lamarck – proposed that by selective
use or disuse of organs, organisms acquired or lost
certain traits during their lifetime.
Use and disuse of organs – organisms develop new
organs or change the structure and function of old
organs.
Continual use of an organ would result in the acquired trait
for a new organ.
 Disuse would result in the disappearance of an organ
because it was no longer needed.

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Inheritance of acquired traits – believed that offspring
would inherit useful structures developed by parents.
Lamarck’s hypothesis is now known to be incorrect. While
organisms do adapt to their environment, an individual’s
genetic makeup cannot change.
 Only genetic variations are passed on from generation to
generation.
 In other words, the discovery of genes proved Lamarck’s
hypothesis invalid.

DARWIN PRESENTS HIS CASE
On the Origin of
Species – Darwin’s
book, published in
1859.
 Here he poses a
mechanism for
evolution that he
called natural
selection.

EVOLUTION BY NATURAL SELECTION
Struggle for Existence – members of each
species compete to obtain food, living space, and
other necessities for life.
 Fitness – the ability of an individual to survive
and reproduce in its specific environment.
 Adaptation – any inherited characteristic that
increases an organism’s chance for survival; gives
an organism an advantage in its particular
environment.


Successful adaptations enable organisms to become
better suited to their environment and thus better
able to survive and reproduce.
EVOLUTION BY NATURAL SELECTION

Survival of the Fittest – individuals that are
better suited to their environment and have
adaptations that enable fitness, survive and
reproduce most successfully. Thus, passing the
genes that allow them to be better suited on to
their offspring. Individuals with characteristics
that are not well suited to their environment
have low levels of fitness, and either die or leave
few offspring.


Darwin referred to this as natural selection.
Over time, natural selection results in changes in the
inherited characteristics of a population. These
changes increase a species’ fitness in its environment.
DESCENT WITH MODIFICATION


Descent with Modification – over time,
natural selection produces organisms that have
different structures and establish different
niches. As a result, species today look different
from their ancestors.
Common Descent – all species – living and
extinct – are derived from common ancestors,
therefore a single “tree of life” links all living
things.
SUMMARY OF DARWIN’S THEORY
1.
Variation exists within a species.
2.
Organisms produce more offspring than can survive.
3.
All organisms compete for limited natural resources
(food, water, shelter).
4.
Each unique species has different advantages and
disadvantages in the struggle for existence.
5.
The environment selects organisms with beneficial
traits.

Natural selection – individuals with adaptive traits have a
greater chance than others to survive and pass on the genes
for these beneficial traits to their offspring.
EVIDENCE OF EVOLUTION
1.
The fossil record
2.
Geographic distribution of living species
3.
Similarities in embryology/early development
4.
Similarities in anatomical (body) structures
5.
Biochemical analysis
6.
Ice core drillings
THE FOSSIL RECORD
•
This stratigraphic
column shows the
order in which
organisms appeared.
Each layer represents
a particular time
frame and shows an
organism which was
found during that
time.
•
The oldest fossils
appear in lower
layers, and the most
recent fossils at the
top. This allows for
placement of fossils to
be used as an aid in
dating the organism
found.
GEOGRAPHIC DISTRIBUTION

Armadillos and anteaters descended from a
common ancestor, yet on different continents?
GEOLOGIC
PROCESSES
•
•
•
Tectonic plates have
drifted atop Earth’s
mantle
Locations of
continents and ocean
basins influence
Earth’s climate
Species move, adapt
to new environments
EMBRYOLOGY
ANATOMICAL EVIDENCE

The more closely related a species, the more similar
their structures will be.


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Homologous structures – body parts with structures that
are very similar, even though they have entirely different
functions.
Ex. Bones in a whale’s flipper, a human’s arm or bat’s wing
Vestigial structures – body parts that have degenerated or
reduced in size and seem to serve no function.
Ex. Tail-bone, wisdom teeth, appendix
Boas and whales – small hip and leg bones (pelvic girdle)
Analogous structures – body parts that have the same
function but are NOT similar in structure.
Ex. Wing of a bird and wing of a butterfly
HOMOLOGOUS STRUCTURES
VESTIGIAL STRUCTURES
Vestigial organs associated with eye structures
Vestigial remains of a pelvic girdle in a whale
ANALOGOUS STRUCTURES
• Analogous structures
are a contrast to
homologous
structures.
• These structures are of
no use in classifying
organisms or in working
out their evolutionary
relationships with each
other.
BIOCHEMICAL ANALYSIS


Biochemical analysis – study of chemicals (DNA,
cells, proteins, blood, enzymes) that are within
organisms.
Nutall precipitation technique – used to test
similarities of blood proteins, particularly antibodies.


The stronger the agglutination, the more closely related
the organisms.
Species - a group of similar organisms that share a
common ancestor.

species do not reproduce outside the group and produce
fertile offspring.
GENES AND VARIATION
Changes in genes produce heritable variation on
which natural selection can operate.
 Gene pool – consists of all genes, including all
the different alleles that are present in a
population.
 Relative Frequency – the number of times an
allele occurs in a gene pool, compared with the
number of times other alleles for the same gene
occur.

Typically expressed as a percentage
 Has nothing to do with dominant/recessive


In genetic terms, evolution is any change in the
relative frequency of alleles in a population.
GENES AND VARIATION
Inherited variation – changes in genes
provided by nature.
 Artificial selection – “controlled breeding”

Process controlled most directly by humans
 Humans select the variations that they find useful.

SOURCES OF GENETIC VARIATION

Mutation – a change in DNA
Mutations are a source of new genetic material.
 They add genetic material to a population’s gene pool
thereby increasing variation within the population.
 Mutations can be harmful, beneficial or neutral.


Causes of mutations:
Ultraviolet light
 X-rays
 Radioactivity
 Certain chemicals (mutagens)
 Random errors in DNA coding

SOURCES OF GENETIC VARIATION

Gene shuffling – genetic recombination (in
sexual reproduction only)

The 23 pairs of chromosomes found in humans can
form 8.4 million different combinations of genes –
before crossing over.

Gene shuffling produces many different combinations
of genes, but does not alter the relative frequencies of
each type of allele in the population.
SINGLE GENE AND POLYGENIC TRAITS
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The number of phenotypes produced for a given trait
depends on how many genes control the trait.
Single gene trait – a trait controlled by a single gene with
two alleles. (ex. Widow’s peak)
Polygenic trait – trait controlled by two or more genes.
Each of these genes often has two or more alleles. As a
result, one polygenic trait can have many possible
genotypes and phenotypes. (ex. Height in humans).
NATURAL SELECTION ON SINGLE GENE
TRAITS
Populations evolve, not individual organisms.
 Natural selection on single-gene traits can lead to
changes in allele frequencies and thus to
evolution.

NATURAL SELECTION ON POLYGENIC
TRAITS

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Directional selection – when individuals at
one end of the curve have higher fitness than
individuals at another end of the curve,
directional selection takes place.
NATURAL SELECTION ON POLYGENIC TRAITS

Stabilizing selection – when individuals near
the center of the curve have higher fitness than
individuals at either end of the curve.

This type of selection leads to a reduction of variation
in a species.
NATURAL SELECTION ON POLYGENIC
TRAITS

Disruptive selection – when individuals at the
upper and lower ends of the curve have higher
fitness than individuals near the middle.
GENETIC DRIFT
Genetic drift – random change in allele
frequencies that occurs in small populations.
 Founder effect – allele frequencies change as a
result of the migration if a small subgroup of a
population.

EVOLUTION VS. GENETIC EQUILIBRIUM
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Hardy-Weinberg Principle – allele frequencies
in a population will remain constant unless on or
more factors cause those frequencies to change.
Genetic equilibrium – the situation in which
allele frequencies remain constant.
For evolution to occur some external factor must
upset the genetic equilibrium of a population.
EVOLUTION VS. GENETIC EQUILIBRIUM

Five conditions are required to maintain genetic
equilibrium:
1.
2.
3.
4.
5.
There must be random mating.
The population must be very large.
There can be no movement into or out of the
population.
There can be no mutations.
There can be no natural selection.
If these conditions are not met, then genetic
equilibrium will be disrupted and the population will
evolve.
PATTERNS OF EVOLUTION


Macroevolution – the large scale evolutionary
patterns and processes that occur over long
periods of time.
Extinction –
More than 99% of all species that have ever lived are
now extinct.
 Several times in earth’s history, mass extinctions
wiped out entire ecosystems.
 Each mass extinction provides opportunities for
organisms that survive and often results in a burst of
evolution that produces many new species.

PATTERNS OF EVOLUTION
1.
Divergent evolution – the process by which
related species become less alike; evolve into a
variety of species

Leads to speciation –the formation of a new species.


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Also results in adaptive radiation – the process by
which members of a species adapt to a variety of
habitats.


Ex. Polar bears diverged from brown bears
Camels and llamas
Ex. Darwin’s (Galapagos) finches – 13 different variations
Biodiversity is believed to be the result of
speciation and extinction.
PATTERNS OF EVOLUTION

Adaptive radiation – when a single species or small
group of species evolves into several different forms that
live in different ways.
SPECIATION


As new species evolve, populations become
reproductively isolated from each other.
Reproductive isolation – when members of
two populations cannot interbreed and produce
fertile offspring.
TYPES OF REPRODUCTIVE ISOLATION
Behavioral isolation – occurs when two
populations are capable of interbreeding but have
differences in courtship rituals or other
reproductive strategies that involve behavior. (ex.
Birds with different mating songs).
 Temporal isolation – two or more species
reproduce at different times. (ex. Flowers
releasing pollen at different times of the year).
 Geographic isolation – two populations are
separated by geographic barriers. (ex. Colorado
river separates two types of squirrels).

GEOGRAPHIC ISOLATION
The movement of tectonic plates influences
evolution by changing the locations of continents,
causing some species to be geographically
isolated from others.
 Geographic isolation can result from

Mountain ranges
 Volcanic eruptions – lava flows
 Rivers
 Earthquakes
 Deforestation
 Continents
 Islands

TESTING NATURAL SELECTION IN NATURE
SPECIATION IN DARWIN’S FINCHES
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Founders arrive – finches from South American mainland
(species A) populated the Galapagos.
Geographic isolation – birds from species A crossed to
another Galapagos island. The two populations became
isolated from one another and had different gene pools.
Changes in the gene pool – populations on the new island
adapted to their environment, forming population B.
Reproductive isolation – because of their adaptations and
different beaks, species A and B do not mate together if
they come in contact.
Ecological competition – during dry season, individuals
compete for food, and over time birds evolve better beaks
(species C).
Continued evolution – this process continues over several
generations and over time produces the 13 species seen
today.
PATTERNS OF EVOLUTION
Convergent evolution – the process by which unrelated organisms
develop similar characteristics; analogous structures.
• occurs when different species share the same environmental
surroundings
– Ex. Whales and dolphins (mammals) now resemble fish
CONVERGENT EVOLUTION
• Can often lead to cases of mimicry – the evolution of one
organism so it comes to resemble or look like another.
– Ex. Queen Anne’s butterfly closely resembles the toxic
Monarch butterfly.
• Over the course of time, the change of the gene pool of one
species may lead to the change of the gene pool of another
species – coevolution – when two species evolve in response
to changes in each other.
– Ex. Bats and moths
– Flowers and insects
MIMICRY
Queen Anne’s Butterfly
Monarch Butterfly
COEVOLUTION
PATTERNS OF EVOLUTION

Punctuated equilibrium – when long stable
periods are interrupted by brief periods of more
rapid change.
Gradualism – the idea that biological change is slow
and steady. (supported by Darwin)
 Scientists suggest that most new species are
produced by periods of rapid change, because
organisms evolve rapidly to fill available niches.
 Example of punctuated equilibrium –
Dinosaur species dominated Earth for over 100
million years. During this time, most mammals
were small mouse-sized nocturnal organisms.
Following the mass extinction of the dinosaurs, the
small mammals rapidly diversified to fill available
habitats and niches.

EVOLUTION – A SUMMARY

Biological evolution
By natural selection – explains how life changes over
time
 Adaptation or adaptive traits enables an organism to
survive through natural selection to reproduce under
prevailing environmental conditions.
 Biological evolution is based on changes in a
population’s genetic makeup over time.
 Populations evolve due to variations within, but
individuals can’t develop new structures.

AN ANCIENT, CHANGING EARTH
• Earth is constantly changing and
throughout history has had changes in
1.
2.
3.
4.
5.
The atmosphere
Climate
Positions of continents
Geography
Types and number of organisms
GEOLOGY AND A CHANGING EARTH


James Hutton – proposed that layers of rock
form slowly and that rocks are shaped by natural
forces that operate over millions of years.
Charles Lyell – wrote Principles of Geology,
which explained that processes that changed
Earth in the past are still operating in the
present.
ATMOSPHERE AND CLIMATE CHANGES
• Atmosphere
– Changes in the atmosphere were the result
of collisions between earth and large
asteroids (catastrophic events)
• Climate change
– Alternate periods of heating and cooling
– Advance and retreats of ice sheets over
northern hemisphere
INTERPRETING FOSSIL EVIDENCE


Paleontologists – scientists who study fossils in
order to determine animal behavior and climate
conditions of the past.
Paleontologists determine the age of fossils using two
techniques;
Relative dating – the age of a fossil is determined by
comparing its placement with that of fossils in other
horizontal layers of rock.
1.

Radioactive dating – scientists calculate the age of a
sample based on the amount of remaining radioactive
isotopes it contains.
2.


Problems – erosion, earthquake and volcanic activity can
twist, fold and bend rock layers.
More exact method because the decay rate of each element is
known.
Fossil record – provides evidence about the history
of life on Earth. It also shows how different groups of
organisms, including species, have changed over time.
HOW FOSSILS
FORM

For fossil to form,
either the remains of
the organism or some
trace of its presence
must be preserved.
FOSSIL EVIDENCE

Most fossils are formed in sedimentary rock
(mud, silt, clay)
Upper layers = most recent
 Lower layers = older fossils


Types of fossils include:
1.
2.
3.
4.
5.
6.
Casts
Amber – preserved or frozen
Trace fossils
Petrified fossils
Imprints
Molds
GEOLOGIC TIME
SCALE

Geologic time scale
– divisions used to
represent
evolutionary time.
Geologists divide time
into four major eras:
precambrian, the
paleozoic, the
mesozoic, and the
cenozoic eras.
 Each era is subdivided
into periods.

GEOLOGIC TIME SCALE

Precambrian
88% of Earth’s history
 Few multicellular fossils


Paleozoic

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Many vertebrates and invertebrates lived during this
time.
Mesozoic
“The Age of the Dinosaurs”
 Mammals began to evolve during this time.


Cenozoic
“The Age of the Mammals”
 The last 65 million years

FORMATION OF THE EARTH
Geologic evidence shows that Earth is about 4.6
billion years old and was created over many
years.
 Earth was formed from cosmic debris which
collided with on one another over the course of
millions of years.
 Early Earth was extremely hot, and unsuitable
for life because of violent earthquakes and
asteroid impacts.

HISTORY OF THE EARTH
• The evolution of life is linked to the
physical and chemical evolution of
the earth.
• Life on earth evolved in two phases
over the past 4.7 -4.8 billion years
1) Chemical evolution (1 billion
years) of the organic molecules
and systems of chemical
reactions needed to form the
first proto-cells.
2) Biological evolution (3.7 billion
years) of single-celled organisms
and then multicellular organisms
FIRST ORGANIC MOLECULES

1950s – Stanley Miller and Harold Urey tried to
simulate conditions of early Earth in the
laboratory.
Filled flask with fluids and gases similar to those in
Earth’s early atmosphere. Passed electric sparks
through the mixture to simulate lightning. Their
experiments produced amino acids, the building
blocks of ____________?
 This exhibited the process of chemical evolution.

THE PUZZLE OF LIFE’S ORIGINS
FREE OXYGEN
Microfossils of unicellular organisms resembling
bacteria have been found in rocks more than 3.5
billion years ago, which means that they must
have evolved in the absence of oxygen, because
there was little/no oxygen in Earth’s early
atmosphere. (Cyanobacteria)
 Photosynthetic organisms evolved later, which
created a rise in oxygen levels in the atmosphere.
This change likely caused some organisms to
become extinct, while others evolved more
efficient respiration mechanisms which utilized
oxygen.

THE ENDOSYMBIONT THEORY
One large prokaryotic cell containing DNA,
engulfed several other smaller prokaryotic cells
with specialized functions. Together these cells
lived symbiotically and were interdependent on
one another. Collectively, they formed the first
eukaryotic cell, which went on to divide and give
rise to other eukaryotic cells.
 Main Point – one condition necessary for the
evolution of first life on Earth was the presence of
DNA.

THE ENDOSYMBIONT THEORY