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EVOLUTION
A HISTORY AND A PROCESS
DARWIN DEVELOPED A THEORY
OF EVOLUTION
• Ideas From Darwin’s Time
– Evolution is the changes that have altered
life over a very long time.
– Before Darwin’s hypotheses, there were two
predominant hypotheses.
• One was species were fixed in time, or did not
change.
• The other was that Earth was less than 10,000
years old and was unchanging
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Georges Buffon, a French naturalist in the
mid-1700s, suggested that Earth might be
older than a few thousand years by looking at
fossils.
– His observations concluded that the fossils and
some living animals were similar but not
exactly alike.
– In the early 1800s, Jean Baptiste Lamarck
suggested that life evolves.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– He explained that species are not permanent
and that evolution was a process of
adaptation.
– Biologists today look upon adaptation as an
inherited characteristic that improves the
organism’s chances of survival and
reproduction.
– The kangaroo’s hind legs and tail are
examples of adaptation.
ADAPTATION
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Lamarck also hypothesized an explanation for
adaptation that when organisms use or not
use certain body parts, certain characteristics
develop, and these characteristics would be
passed on to the offspring.
• This idea was called inheritance of acquired
characteristics.
• For example, ancient kangaroos developed the
powerful legs jumping and passed them on to their
offspring.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
• This characteristic would have to modify the DNA of
specific genes in order to be inherited, which has
yet to be proven.
– Look at the bonsai tree as an example.
• The Voyage of the Beagle
– This was the royal navy ship that Darwin
began his five year adventure in 1831, upon
graduating from university.
TRAINING, NOT GENETICS
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– He wanted to study geology, plants and
animals that were encountered while charting
the coast of South America.
• Darwin’s Observations
– He observed and collected thousands of
specimens of South American plants, animals,
and fossils from many diverse ecosystems.
DARWINS TRIP ON THE BEAGLE
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Before his voyage, Darwin held to the belief
that the concepts of fixed, or unchanged
species described nature; but during the
voyage his concepts changed.
– Upon his return to England, he believed that
species change as they adapt to their
changing environment.
– Throughout South America, Darwin noticed
DARWIN DEVELOPED A THEORY
OF EVOLUTION
the plants and animals had a South American
character.
– They were distinct from what he had seen in
Europe.
– The fossils he collected supported the
hypothesis that the current species were
descended from ancestral species.
– The Galapagos was his nirvana.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– The Galapagos are volcanic islands about 900
km west of Ecuador.
– He noted that there were many diverse and
unique organisms.
– They were similar, but different, to those he
found on the mainland of South America.
– He also noted difference among the organisms
of each island.
GALAPOGOS ISLANDS
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– The inference was that the organisms adapted
from the mainland to the islands where they
were currently found.
• Ideas From Geology
• Charles Lyell, a geologist, influenced
Darwin.
• Lyell projected that gradual geologic
DARWIN DEVELOPED A THEORY
OF EVOLUTION
changes could explain the physical features of
today’s Earth.
– Examples could include erosion of riverbeds
over, maybe, millions of years that could
result in canyons.
– Earthquakes could cause mountain ranges to
push up slowly over millions of years.
HORSESHOE BEND, AN EXAMPLE OF
EROSION BY THE COLORADO RIVER
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– This would have to mean that the Earth was
much older than previously thought.
– Darwin personally experienced an earthquake
while in Chile.
– He collected ocean fossils high in the Andes,
and thought that earthquakes lifted the sea
floor to the mountains, and brought with it the
marine fossils.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Two conclusions related to geology were
drawn.
• First, mountain building and erosion indicted Earth
being very old.
• Second, the slow and gradual processes occurring
over long periods of time could cause vast changes
on Earth.
– This gradual change in geology led to Darwin’s
evolution hypothesis.
DARWIN AND HIS PUBLIC IMAGE
DARWIN DEVELOPED A THEORY
OF EVOLUTION
• Darwin Publishes His Theory
– Upon return to England, Darwin became
convinced that earth was very old and species
can change through time or adapt.
– He read Thomas Malthus’ theories about
human suffering due to disease, famine, and
homelessness or populations grow too fast
(reach their carrying capacity) and outgrow
their resources.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Darwin applied this to all species.
– In 1844, Darwin wrote his thesis outlining his
ideas but held on to it in order to accumulate
more evidence, consult with his peers, and
receive favorable public press.
– Then, in 1858, another British naturalist, came
to the same conclusion independently working
in Malaysia, causing Darwin to publish his
book The Origin of the Species a year later.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
• Darwin’s Two Main Points
– First, species on Earth originated from
ancestral species.
• Descendants or earliest organisms spread into
different habitats over millions of years and, there,
accumulated different modifications (adaptations)
to the diverse ways of life.
• This he called this decent with modification.
DESCENT WITH MODIFICATION
DESCENT WITH MODIFICATION
DESCENT WITH MODIFICATION: HARE vs.
JACKRABBIT
Large ears of jackrabbit are adaptation to hot environment that
allow it to cool off, while the white fur of the snowshoe hare
camouflages the animal.
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– Second, he argued that natural selection
was the mechanism for evolution.
• This also is known as survival of the fittest.
– This is the process by which individuals well
suited to their environment reproduce more
than those that are not.
– Therefore, “Darwin’s theory of evolution” is
really natural selection.
INHERITED VARIATION MAKES
SNAILS LESS LIKELY TO BE PREY
DARWIN DEVELOPED A THEORY
OF EVOLUTION
– The result of natural selection is adaptation
and is another way of defining evolution.
– Evolution can also mean the history of life on
Earth, from the earliest microbes to the
complexity of organisms found today.
REVIEW: CONCEPT CHECK 14.1,
page 298
1. How did the work of Lyell and Malthus influence
Darwin as he developed his theory of evolution?
2. What characteristics of the Galapagos Islands were
particularly important for Darwin?
3. What is natural selection?
4. Which of the following is an adaptation: the sharp
teeth of a house cat, or a scar on the cat’s ear?
Explain.
EVOLUTION HAS LEFT MUCH
EVIDENCE
• The Fossil Record
• Fossils, as you know, are preserved
remains of organisms that lived in the
past.
• Most are found in sedimentary rocks.
– These are formed from sand and silt that has
eroded from the land and deposited and
EVOLUTION HAS LEFT MUCH
EVIDENCE
carried by waterways to the seas and
swamps, where they settle to the bottom.
• Over a long period of time, there comes to be lots
of this material piling up on top of one another,
compressing the older sediments on the bottom
into rock.
• Layers, or rock strata, form when the rates of
sedimentation or types of particles forming the
sediments vary over time.
SEDIMENTARY ROCK
SEDIMENTARY ROCK
FOSSILS AND SEDIMENTARY ROCK
EVOLUTION HAS LEFT MUCH
EVIDENCE
– Fossils form if they are caught in the sediment
after they die and are preserved.
– The oldest layer are at the bottom and
youngest at the top.
– The fossil record is the chronologic collection
of the remains within each layer, and provides
historical evidence of Earth’s changing life.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– The oldest fossil (chemical traces) was found
in Greenland and dates to 3.8 billion years
ago.
– The first life on Earth was prokaryotes
(bacteria and archaea) found in rocks about
3.5 billion years old.
– The younger layers of rock give the evolution
of the various eukaryotic organisms.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– The first nuclear cell, a single cell, was found
to be 1.5 billion years old.
– Extinct species’ fossils aid in reconstructing the
earliest days on Earth.
– Paleontologists, who study ancient life, have
found that whales evolved from land animals
that had four limbs, but lost the hind limbs
eventually.
EVOLUTION OF WHALES
EVOLUTION OF WHALES
EVOLUTION HAS LEFT MUCH
EVIDENCE
• Geographic Distribution
– Darwin noticed the differences and similarities
of organisms on the different continents he
visited.
– From these observations, he thought that the
modern organisms evolved from those in the
past.
– He questioned the similarity between animals
EVOLUTION HAS LEFT MUCH
EVIDENCE
of the South American tropics and the animals
of the South American desert; and their nonsimilarity to animals in the African tropics.
– Why do most of the marsupials (pouched
mammals) live in Australia and few placental
animals (complete their embryonic
development before birth), deer and squirrels,
live there.
GEOGRAPHIC DISTRIBUTION
EVOLUTION HAS LEFT MUCH
EVIDENCE
– Placental mammals can thrive in Australia.
– The belief is that the diverse marsupial species
evolved from marsupial ancestors on an island
continent where no placental animals were
found.
– Geography , according to Darwin, played a
strong part in what organisms were found
where.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– Islands with similar climates in different parts
of the world contained in the past and present
organisms that identify with the closest large
land masses.
• Similarities in Structure
– There are similarities among structures of
different species that provides evidence of
evolutionary history.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– All mammals have the same skeletal parts in
their forelimbs, but the functions might be
different.
• For example, there are similarities in structure
between the bat’s wing and the whale’s flipper, but
the function couldn’t be more different.
– Similar structures in species that share a
common ancestor are homologous
structures.
HOMOLOGOUS STRUCTURES
HOMOLOGOUS STRUCTURES
EVOLUTION HAS LEFT MUCH
EVIDENCE
– Looking at homologous structures supports
the evidence that adaptation takes place from
the ancient species to the more modern
species.
– Similar structures take on new functions with
adaptation which supports the descent with
modification theory.
– Another interesting fact is vestigial
structures,
EVOLUTION HAS LEFT MUCH
EVIDENCE
which are remnants of structures that at one
time had important functions , but in the more
modern species, have no or little function.
– This can be seen, also, as similar structures
having importance in one species of mammals
but not in others.
– Often the vestigial organs are reduced in size,
such as the hind limbs of mammals with four
EVOLUTION HAS LEFT MUCH
EVIDENCE
limbs but small vestigial hipbones in whales.
– The natural selection theory supports the
explanation for vestigial structures and the
known process of inheritance, which is the
survival and reproduction of individuals with
genes for reduced versions of the structures.
– The presence of these structures gives truth to
the theory that certain species descended
from a common ancestor.
VESTIGIAL STRUCTURES
EVOLUTION HAS LEFT MUCH
EVIDENCE
• Similarities in Development
– Darwin also used comparison of different
organisms to prepare his hypothesis.
– He noted that embryos of closely related
organisms have similar stages of development.
• Vertebrates have pouches on the sides of their
throats in one of their embryonic stages.
• Fish, frogs, snakes, birds, and primates look alike in
this stage.
SIMILARITIES IN DEVELOPMENT
SIMILARITIES IN DEVELOPMENT
EVOLUTION HAS LEFT MUCH
EVIDENCE
– As these different vertebrates develop, they
assume their own distinctive features.
• For example, there is a common pattern in the
development of forelimbs in different mammals.
• Molecular Biology
– Recently, there is clear evidence in evolution
from the molecular history of organisms.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– While there are similarities in sequencing, it is
less so in unrelated individuals than in related
individuals.
– Biologists are looking at the sequencing of
different species as to the genes and proteins
produced.
– If they match closely, then their sequencing
must have been inherited from a recent
common ancestor.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– The opposite is also true, that the less they
resemble each other in DNA and protein
sequencing, the less likely they have a
common ancestor.
– With DNA and protein analysis, biologists can
test these hypotheses.
– Fossils and anatomy relate humans,
chimpanzees, and gorillas.
EVOLUTION HAS LEFT MUCH
EVIDENCE
– This hypothesis is testable: if the humans and
primates are related, then they would share
similar DNA and protein synthesis.
• Data from the amino acid sequencing of
hemoglobin support this hypothesis.
– There is only 5% difference in the sequencing
between humans and chimpanzees.
AMINO ACID SEQUENCING
BETWEEN PRIMATES
AMINO ACID SEQUENCE BETWEEN
SPECIES
YOUR COUSIN: A CHIMPANZEE??
EVOLUTION HAS LEFT MUCH
EVIDENCE
– Darwin ‘s hypothesis that all life forms are
related has been shown to be true by the
common genetic code shared by all species.
REVIEW: CONCEPT CHECK 14.2,
page 304
1. Why are older fossils generally in deeper
rock layers than younger fossils?
2. How can evolutionary theory explain why
Australia is home to relatively few native
placental mammals?
3. What are homologous structures?
4. What can you infer about species that differ
significantly in their DNA sequences?
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• Darwin’s Theory of Natural Selection
– Populations are groups of individuals living
in the same area at the same time.
– A species that came from a mainland, over
time, living on an isolated island makes up a
separate population that would adapt to the
local conditions.
– Eventually, the isolated population would
DARWIN’S FINCHES
DARWIN’S FINCHES
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
become more and more different, with the
eventuality that a separate species would
evolve.
• This is what happened to Darwin’s finches on the
Galapagos.
– Observations Lead to a Question
• One finch from South America gave rise to 13
different finches on the Galapagos.
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• The explanation that these different finches
adapted to their different habitats on the different
islands and developed different beaks in response
to the food available.
• Darwin would say this happened because of natural
selection.
– More Observations Lead to an Idea
• Natural selection was based on two sets of
observations.
NATURAL SELECTION
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• The first was drawn from Malthus’s ideas about
humans and recognized that all species can produce
numbers greater than can be supported.
• Remember carrying capacity and competition if too
many of a species occupy an habitat.
• Most of the time, only a small amount of offspring
will survive.
• The second observation was the variation seen
among the individuals of a population.
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• Remember that variation is that concept that
refers to the differences among members of the
same species.
– This variation can be and is inherited.
• From these two observation came the theory of
natural selection which tells us that individuals with
inherited traits are best suited to their environment
and will survive and reproduce than those less fit.
• This is also known as survival of the fittest.
NATURAL SELECTION
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• Passing these traits to each of the next generation
produces only advantageous traits in the new
offspring.
• According to Darwin, natural selection could cause
two isolated populations of the same species to
become separate species by adapting to the
different environments, such as the finches did.
• Artificial Selection
– Artificial selection is selective breeding of
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
plants and animals to produce offspring with
selected traits that are valued.
– Darwin noted that breeders allowed only those
plants and animals with the desired traits to
reproduce, and that over s relatively short
period of time a great deal of changes could
be produced.
– Naturally, his conclusion was that over
ARTIFICIAL SELECTION
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
thousands of generations, natural selection
could cause major changes.
– The major difference between the two is that
in one humans select the trait desired in the
offspring while in the other nature selects
what is important to survive in that particular
environment.
– Evolutionary adaptation is the result.
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
• Pesticides-Natural Selection in Action
– Insects have the uncanny ability to adapt very
well, especially to the various pesticides
utilized.
– Early applications to rid fields of pests works
great but then adaptation occurs and less and
less insects are eliminated.
– An example is the flour beetle (Tribolium
PESTICIDE RESISTANCE
PESTICIDE RESISTANCE
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
castaneum, for which malathion worked well
but now, even in high doses, has no effect.
– Genetically, each generation beetle passed on
to the next generation an even greater
resistance to the pesticide, and with
evolutionary changes the pesticide was no
longer efficacious.
– Therefore, natural selection offers two key
points.
DARWIN PROPOSED NATURAL SELECTION AS
THE MECHANISM OF EVOLUTION
– Natural selection is a process of screening
traits that are available.
• The pesticide did not create the resistance but
selected those that developed it and survived
– Natural selection likes those characteristics in
varying populations that fit the specific
environment.
• There was no advantage to pesticide resistance
until the pesticide application changed the
environment.
REVIEW: CONCEPT CHECK 14.3,
page 308
1. In Darwin’s view, what conditions lead to
a struggle for existence among
individuals in a population?
2. What is the goal of artificial selection?
3. Why does a specific pesticide become
less effective over time?
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• Populations and Their Gene Pools
– Populations are groups of individuals
belonging to the same species and is the
smallest level in which evolution can take
place.
– It is a mistaken belief that individuals evolve
and not populations.
– Natural selection affects individuals but it is
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
the entire populations that adapts over time.
– Gene pools are composed of all the alleles in
all individuals that make up a population.
– This is where the next generation “draws’ its
genes from and where genetic variation is
born and stored.
– Certain animals, such as horses, have different
coloration due to each horse’s own
GENE POOLS
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
combination of genes.
– This is the result of genetic recombination,
seen more frequently in which reproduction is
sexual.
• Meiosis and gene shuffling produces the different
combinations.
• Changes in Gene Pools
– Genetic variation, caused by mutations and
recombination, are random.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– Outcomes of these gene recombinations can’t
be predicted but natural selection is not
random.
– Environment dictates survival and reproductive
success so those alleles that lead to this are
more common.
– Frequency of alleles, or how often certain
alleles appear in a gene pool, can change.
GENE POOLS AND FRQUENCY
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– One can merge Mendel’s and Darwin’s
theories to come up with evolution based on
genetic changes.
– Microevolution is the changes in the
frequencies of alleles from generation to
generation.
– Some populations do not change or undergo
evolution.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– This is known as the Hardy-Weinberg
equilibrium, and means that the frequency
of alleles in a gene pool remains constant over
time.
– While it is rarely seen for long in nature, the
concept allows for a baseline to recognize
when that gene pool is changing.
– Genetic drift and natural selection account for
changes in a gene pool.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• Genetic Drift
– Changes in gene pools of populations, due to
chance, is known as genetic drift.
– In the slide that follows, one can see two
phenotypes due to three different genotypes.
– Chance dictates which plants reproduce, so
that by the third generation, there could be no
recessive plants.
GENETIC DRIFT
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– While genetic drift can affect all populations, it
is most felt in smaller populations, because
probabilities have less of a chance to be
correct.
– The Bottleneck Effect
• Major disasters have profound effects on sizes of
population, e.g. the recent earthquake in Haiti.
• Reduction in population results in reduction of the
gene pool.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• Chance will allow some alleles to be more frequent
in the survivors, others to be eliminated altogether.
• This genetic drift is known as the bottleneck
effect, and decreases genetic variation in
populations.
• This could result in loss of adaptation to
environments.
– Cheetahs were affected by the last ice age and recently
hunted almost to extinction.
– Their pool have decreased as a result and they may not be
able to adapt to disease or other challenges.
BOTTLENECK EFFECT
BOTTLENECK EFFECT
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– Founder Effect
• When isolated islands are inhabited, they are done
so by only small colonies with a smaller genetic
make-up which represents the gene pool of the
larger population from whence the colonies came.
• Chance will reduce this variation.
• This is known as the founder effect because the
change relates to the genetic make-up of the
founders of the colony.
– A prime example is Darwin’s finches.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• Gene Flow and Mutation
– Gene Flow
• Exchanges of genes with other populations is gene
flow, and occurs when animals in heat exchange
gametes between populations.
• This is seen often in flowers when pollen can be
exchanged between different populations .
• This results in the reduction of genetic differences
between populations.
GENE FLOW
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• Mutation
– Remember, mutation is any change in the
organism’s DNA.
– Natural selection or genetic drift (or both) can
influence whether the frequency of a new
mutation increases in a population.
• The albino deer has the advantage in the winter but
lacks it the other three seasons.
• This can and does present a dilemma that would
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
hinder the frequency of this allele.
– Over a long period of time, mutations play key
roles as the original sources of genetic
variation in natural selection.
– These become most important in asexual
reproduction where cloning occurs.
• Bacteria can produce favorable mutation rapidly
while in sexual reproduction variation occurs
MUTATIONS AND ALBINO DEER
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
because of scrambling of existing alleles, including
those that occurred as a result of mutations in
earlier generations.
• Natural Selection and Fitness
– Microevolution occurs with genetic drift, gene
flow, and mutation but not necessarily
adaptation as these can be due to chance.
– Only natural selection leads to adaptation.
“STRUGGLE” & “FITTEST”
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– With natural selection, one gets chance and
sorting.
• Chance from mutations and genetic recombination
– Sorting, which is not random, comes from
differences in reproductive success among the
members of the varying population.
– Struggle for existence or survival of the fittest
are used to describe natural selection.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– Struggle or fittest involves biological
definitions, not competitions.
– Fitness is the contribution that individuals
make to the gene pool of future generations
compared to the contributions of other
individuals.
– All that really counts in fitness is reproductive
ability.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
• A Return to the Galapagos
– “Darwin’s finches” are one of the best living
laboratory specimens of natural selection.
– Rosemary and Peter Grant and their students
have studied these finches each year on
Daphne Major, an island in the Galapagos no
bigger than a football field.
ROSEMARY AND PETER GRANT
DAPHNE MAJOR
FINCHES OF DAPHNE MAJOR
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– Using the data collected from their studies,
they have been better able to explain natural
selection.
– The medium ground finches use their beaks to
crush seeds, not large ones but mostly small
ones because they are easier to crush.
– There are dry and wet seasons with more or
less small seeds, so to survive the birds must
eat the large seeds as well.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– Some birds have larger beaks that allow them
to more easily crush the larger seeds, and
therefore, increase their survivability.
– These larger beaks are then passed on to
future generations, and reproduction is
increased in this population while smaller beak
birds do not reproduce.
MICROEVOLUTION IS A CHANGE
IN A POPULATION’S GENE POOL
– When wet seasons return, the smaller beaked
birds then flourish and reproduce in greater
numbers.
THE GRANTS’ RESULTS
REVIEW: CONCEPT CHECK 14.4,
page 316
1.
2.
3.
4.
5.
What is a gene pool?
How has genetic drift affected the world’s populations of
cheetahs?
Describe what is meant by a “biologically fit” organism.
Describe the Grant’s hypothesis about how environmental
conditions led to microevolution among the finches of Daphne
Major.
What are two main forces of evolutionary change in gene
pools?
EVOLUTIONARY BIOLOGY IS
IMPORTANT IN HEALTH SCIENCE
• Natural Selection and Sickle Cell Disease
– Sickle cell disease creates an abnormal shape
to the red blood cell resulting in decreased
hemoglobin capacity and clumping of the cells.
– In some African communities, its incidence is
1:25.
– It is caused by a recessive allele and you must
be homozygous.
EVOLUTIONARY BIOLOGY IS
IMPORTANT IN HEALTH SCIENCE
– Heterozygous individuals are carriers and also
possess resistance to malaria.
– The heterozygous individual is found in
greater proportions in those areas of Africa
where malaria is indigenous
– While only 4% are homozygous, 32% are
heterozygous and thus protected from
malaria.
SICKLE CELL DISEASE AND ALLELE
EVOLUTIONARY BIOLOGY IS
IMPORTANT IN HEALTH SCIENCE
• Evolution of Antibiotic Resistance in
Bacteria
– Antibiotics are used to kill or slow the
growth of bacteria.
– Too much usage, however, can lead to
antibiotic-resistant populations caused by
natural selection, just as in pesticide
resistance in insects.
REVIEW: CONCEPT CHECK 14.5,
page 319
1. Under what conditions is the sickle cell
allele beneficial to a heterozygous
individual?
2. Identify a possible risk of overuse of
antibiotics.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
• What is a Species?
– The biological species concept defines a
species as a population or group of
populations where the members have the
ability to breed with one another in nature and
produce fertile offspring.
– Members of one species, however, cannot
successfully interbreed with members of other
species.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
• From Microevolution to Macroevolution
– Evolution can be explained by microevolution
and adaptation, but if that were all that
happened, then Earth’s inhabitants would only
be a highly adapted version of the first form of
life.
– If microevolution refers to the change in the
allele frequencies within a population, then
macroevolution refers to more dramatic
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– Macroevolution refers to more dramatic
biological changes, many found in fossil
records.
• These include the origin of different species
• The extinction of species
• The evolution of major new features, such as wings
or flowers
– Speciation is the origin of new species which
is the main focus of macroevolution.
SPECIATION
With speciation comes biological diversity.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
• Reproductive Barriers Between Species
– Frogs don’t mate with flies or ferns.
– Do species that are not so different mate?
– Remember, a species is a group of organisms
that can reproduce.
– Can species that are similar and closely related
interbreed?
EASTERN AND WESTERN SPOTTED
SKUNKS: REPRODUCTIVE ISOLATION
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– The example in the textbook is the western
and eastern spotted skunks, which don’t
interbreed even when their habitats overlap.
– They don’t because of reproductive isolation
and include some of the following ideas.
– Timing
• They have different breeding seasons, as these
skunks do (western in fall, eastern in late winter).
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– Behavior
• The two similar species may have different
courtship or mating behaviors.
• The example here is the eastern and western
meadowlark, which have different songs, even
though their ranges overlap.
– Habitat
• They are adapted to different habitats, even though
they are in the same general location, such as the
EASTERN AND WESTERN MEADOWLARK:
BEHAVIORAL ISOLATION
THREE-SPINED STICKLEBACK FISH
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
• three-spined sticklefish of British Columbia which
inhabit different parts of the same lake but don’t
interbreed.
– Other Reproductive Barriers
• Dissimilar reproductive structures
• Transfer of pollen by insects to plants of a single
species
• Those that present themselves after fertilization
– Hybrid zygotes that fail to develop or are infertile as adults
HORSE→MULE=DONKEY:
REPRODUCTIVE ISOLATION
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– Reproductive isolation results from a
combination of two or more barriers.
– These present themselves as an effect of
adaptation.
– This could account for the differences between
the eastern and western spotted skunks and
presented itself in their ancestors when the
two species were isolated in different
locations.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– New species arise if reproductive isolation
keeps species separate after the species arise.
• Geographic Isolation and Speciation
– Because of the ever changing geography of
Earth, populations of species can be
separated.
– Mountain ranges, glaciers, earthquakes, and
island colonization can separate populations.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– This is called geographic isolation.
– A prime example is the antelope squirrel
where two species became separated by the
Grand Canyon.
– Once a small splinter population becomes
separated, new species can develop.
– It can follow its own evolutionary course.
ANTELOPE SQUIRRELS: NORTH
RIM vs. SOUTH RIM
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– This is where genetic drift comes into play
where changes in allele frequency caused by
the genetic drift and natural selection can
accumulate in the separate population,
causing it to be less and less like the main
population.
– Many population fail to survive this isolation.
– Speciation occurs only if one population can
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– no longer breed with the other population,
even if they come back into contact.
• In one, the changes do not prevent interbreeding,
and the populations remain one species.
• In the other, evolution has prevented them from
interbreeding and two species result.
• Adaptive Radiation
– Islands seem to have conditions that favor
speciation.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– Only a few organisms can be the first to
inhabit a new island, and they undergo
evolutionary change to survive.
– These “new” organisms can move on to other
islands in the group where “new” species also
evolve.
– New and varying species may evolve through
genetic drift and adaptation to the different
habitats.
ADAPTIVE RADIATION
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– This results in adaptive radiation, which is
evolution from common ancestors that result
in new and diverse species that have adapted
to the new environments.
• One of the best examples of adaptive radiation is
the Hawaiian Islands.
• The Tempo of Speciation
– Species can evolve gradually or rapidly.
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– This is known as punctuated equilibrium
with species diverging in spurts of rapid
change.
– While over a period of a few million years may
seem long, over the lifetime of Earth, this is
but a short period.
– Fossil records indicate that successful species
last about one to five million years.
EVOLUTIONARY TIME
GRADUALISM vs. PUNCTUATED EQUILIBRIUM
THE DIVERSITY OF LIFE IS BASED
ON THE ORIGIN OF NEW SPECIES
– Most of the species changes occur in the first
50,000 years which is a very short period of
time.
– This theory does not negate the theory of
natural selection because adaptation and
natural selection occur when a species is
young.
REVIEW: CONCEPT CHECK 15.1,
page 330
1. Why are donkeys and horses considered different
species?
2. What is macroevolution?
3. Give an example of a reproductive barrier that may
separate two similar species.
4. Describe conditions that could make a new island a
likely place fro adaptive radiation.
5. How does punctuated equilibrium relate to Darwin’s
theory of natural selection?
EVOLUTION IS USUALLY A
REMODELING PROCESS
• Refinement of Existing Adaptations
– Adaptations such as fins and flippers for
swimming animals, bodies sleek for flying,
eyes for sight, or flowers for attraction are
forms of natural selection.
– Eyes, for example, can be seen in various
stages of development in mollusks such as
squids, octopuses, snails, and clams.
DEVELOPMENT OF EYES IN MOLLUSKS
DEVELOPMENT OF EYES IN MOLLUSKS
EVOLUTION IS USUALLY A
REMODELING PROCESS
• Adaptation of Existing Structures to New
Functions
– Over time, certain existing structures in
organisms have evolved from their original
function to something different.
– Chitin, the exoskeleton of arthropods (insects,
spiders, scorpions, and lobsters) is one
example.
EVOLUTION IS USUALLY A
REMODELING PROCESS
– Originally in the ocean the chitin protected the
animal from predators, while on land it took
on an additional function, to protect it against
loss of body water by evaporation.
– Penguins’ flippers have evolved from wings for
flight to flippers for swimming.
• Evolution and Development
– Embryology can answer some of the questions
ARTHROPODS AND CHITIN
PENGUINS’ FLIPPERS
EVOLUTION IS USUALLY A
REMODELING PROCESS
that arise as to the evolutionary remodeling of
body forms.
– Embryology is the study of the development
of multicellular organisms from fertilized eggs
to formed organisms.
– Embryologists look at the genes that control
the development of organisms.
– One study is of homeotic genes that control
the placement of body parts.
EVOLUTION IS USUALLY A
REMODELING PROCESS
– Mutations in this area can lead to flies
developing legs where antennae should be, or,
in most cases, less subtle changes in the
developmental process.
– Remodeling can occur over the short term or
long term depending on the environment of
the organism.
– Development of feet in different salamanders
is an example.
EVOLUTION IS USUALLY A
REMODELING PROCESS
• The tree salamander vs. the ground or
water salamander have different feet
depending on the usage.
– Shorter toes and more webbing in the tree
salamander occurs because growth of these
appendages ends sooner than the rest of the
body as it adapts to the tree.
GROUND AND TREE SALAMANDERS
REVIEW: CONCEPT CHECK 15.2,
page 334
1. How can evolution explain the range of
complexity of eyes in modern organisms?
2. Give an example of evolutionary remodeling
of an existing structure to a new function.
3. Identify one possible event during an
organism’s embryonic development that can
result in a change in body form.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
• How Fossils Form
– We previously learned that fossils form after
being covered by layers of sediment.
– The hard parts are preserved while the soft
parts decay.
– In some cases, minerals from groundwater will
penetrate the tissues and replace the organic
material which then becomes petrified.
FOSSIL DEVELOPMENT
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– In rare cases, some of the organic material
still exists and DNA can be analyzed form it.
– Footprints, burrows, waste material from the
organisms gives clues as to its ambulation,
diet, habitat, and digestive process.
• The Fossil Record and Geologic Time Scale
– Fossil records tell us about macroevolution.
MAMMOUTH REMAINS
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– They tell us the history of Earth.
– The geologic time scale organizes earth’s
history into three ages: Paleozoic, Mesozoic,
and Cenozoic eras.
– The eras are further divided into shorter time
spans called periods.
– Periods can be divided into epochs.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– Time between periods is marked by major
changes in living organisms.
– At the beginning of the Paleozoic Era
(Cambrian period), multicellular organisms
with hard parts developed.
– Boundaries between eras and periods are also
delineated by extinctions.
GEOLOGIC TIME SCALE
GEOLOGIC TIME SCALE
GEOLOGIC TIME SCALE
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
• Dating Fossils
– Relative ages of fossils reflect the order in
which groups of species existed compared to
each other.
• Younger on top and older on bottom.
– Actual ages, or absolute ages, of fossils is
made by radiometric dating, which is based on
the measurement of certain radioactive
isotopes in objects.
RELATIVE DATING
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– Radiometric dating utilizes measurements
of radioactive isotopes in objects.
• It is utilized to measure absolute ages of rocks and
fossils.
• All radioactive isotopes have a standard rate of
decay.
– It’s half-life is that amount of time that it
takes for 50% of the original sample to decay.
RADIOMETRIC DATING
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– Half-lives are not affected by temperature,
pressure, or any other environmental
conditions.
– Radioactive isotopes with long half-lives are
used to date rocks.
• Uranium-238 is used to date rocks from
Precambrian time, since it has a half-life of 4.5
billion years.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
• There is no U²³⁸ in living organisms, but it occurs in
molten lava and volcanic rock.
• With the formation of the volcanic rock, no
additional U²³⁸ is incorporated.
• The original amount of isotope decays, eventually
forming lead(Pb)-206.
• Measuring and comparing U²³⁸ to Pb²⁰⁶, dating can
be made.
• Similarly, fossils found in these rocks can be dated.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– Fossils, themselves, can also be dated since
they contain isotopes of carbon that
accumulated when they were alive (C¹² to C¹⁴).
• Plants utilize both for photosynthesis and animals
consume plants for food.
• After the animal dies, the decay continues, and the
changes in C¹⁴ to C¹² can be measured with calculations
used to determine how long the organism has been
dead.
RADIOACTIVE DATING
RADIOACTIVE DATING
CARBON DATING
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– This carbon dating is only good for recent
fossils since C¹⁴ has a half life of 5,730 years.
If the fossils are older than 50,000 years,
longer half-life isotopes (U²³⁸) must be used.
• Continental Drift and Macroevolution
– Earth is made up of seven tectonic plates.
– Landmasses and oceans are part of these
plates and change position as a result of
movement known as continental drift.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– The plates are known to move at a rate about
1 to 16 cm per year.
• For example, North America and Europe are drifting
apart about 2 cm per year.
• Finding similar fossils on different continents can be
attributed to this plate movement.
– Similar Mesozoic fossils were found in Brazil and Africa.
– Plants and animals of Australia are drastically different
than the rest of the world because Australia became an
isolated landmass and the organisms evolved independent
of those on other continents.
PLATE TECTONICS
CONTINENTAL DRIFT
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– About 250 million years ago, at the end of the
Paleozoic Era, a Pangaea was present or one
landmass (or supercontinent).
– This resulted in: lower sea levels, draining of
shallow coastal seas, destruction of shallow
ecosystems, drier and more extreme climate
changes inland, competition among species,
and ultimately extinction of large amounts of
species.
PANGAEA
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– About 180 million years ago, the Pangaea
began to drift apart and each land mass
became isolated and created separate
evolutionary beginnings.
– Each species on each continent would develop
based on their environment and would have
diverged in their evolution as they adapted.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
• Mass Extinctions
– Examining fossil records reveals that there
have been long periods of stability interrupted
by brief episodes of great species loss which
are known as mass extinctions.
– At the end of the Cretaceous period, about 65
million years ago, the dinosaurs began to
disappear.
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– Before that there were dinosaurs for 150
million years.
– In less than 10 million years, they disappeared
altogether.
– Scientists have been as a loss for the reasons
for this calamity but look at the receding seas,
cooling climate, a meteor striking the Yucatan
Peninsula causing pollution and lack of
photosynthesis for plant production.
DINOSAUR EXTINCTION
THE FOSSIL RECORD PROVIDES
EVIDENCE OF LIFE’S HISTORY
– There have been about 5 or 6 mass extinction
recorded in the history of the Earth, over the
last 600 million years.
• 90% of the marine animals were lost at the end of
the Permian period.
– After each of these periods, there has been
adaptive radiation of some of the survivors,
for example mammals at the end of the
Cretaceous period.
REVIEW: CONCEPT CHECK 15.3,
page 340
1. Which parts of organisms are most commonly found
as fossils?
2. What main characteristics distinguishes the fossil
record of the Paleozoic Era from that of the
Precambrian Era?
3. How are the relative ages of fossils in sedimentary
rock determined?
4. How does a mass extinction change conditions for
species that survive?