Download Evolution and Natural Selection

Evolution and
Natural Selection
How life has changed on
Earth.
The Theory of Evolution
•Evolution is the gradual change in
a species over a long period of
time.
•The evolution of a species is the
result of an individual organism
struggling to survive in a given
environment.
•A scientific theory is a wellsupported testable explanation of
phenomena that have occurred
in the natural world
•There has been no credible
evidence presented to disprove
evolution
The Theory of Evolution
•Individuals with the best traits or
adaptations will have the best
chance to survive.
•The individuals that survive then
have the chance to reproduce
and pass those traits to their
offspring.
The Theory of Evolution
•Charles Darwin was the first person
to successfully describe the
process of evolution, which he
titled, “Natural Selection”
•Darwin traveled the world on the
H.M.S. Beagle.
•He made observations about the
different types of life he found on
the different continents and
remote islands.
•During his travels, Darwin made
numerous observations and
collected evidence that led him to
propose a hypothesis about the
way life changes over time.
•That hypothesis has become the
theory of evolution.
•Darwin collected the preserved
remains of ancient organisms,
called fossils.
•Some of those fossils resembled
organisms that were still alive.
•Others looked completely unlike
any creature he had ever seen.
Natural Selection
•Darwin’s Theory of Natural
Selection is broken down into a
few main ideas.
–Overproduction
–Variation
–Competition
–Selection
Natural Selection
•Overproduction- Individuals of a
species will have more babies
than will be able to survive.
–Insects will produce hundreds of
babies each year
–Fish will lay hundreds of eggs
–Birds will lay a few eggs
–Mammals will produce many
babies each year
Natural Selection
•Variation- Each of the babies that
are produced by the parents will
be a little bit different genetically.
–There will be slight changes in
size, color, speed, development,
etc.
Natural Selection
•Competition- each individual that
is produced wants to survive. It will
compete with its own species and
other species to survive.
–Finding food and water
–Avoiding predators
–Attracting mates
–Obtaining shelter or a territory
Natural Selection
•Selection- The individuals with the
best traits will survive and have the
opportunity to pass on its traits to
its offspring.
•Evolution occurs when these good
traits build in the population over
many generations and the bad
traits are eliminated by the death
of the individuals.
•Darwin noted that plant and
animal breeders would breed only
the largest hogs, the fastest horses,
or the cows that produced the
most milk.
•Darwin termed this process
artificial selection.
•Artificial selection is the selection
by humans for breeding of useful
traits from the natural variation
among different organisms.
•Common in dogs, bird species, live
stock (pigs, cows, horses), and
plant species
The Struggle for Existence
•Darwin realized that high birth
rates and a shortage of life's
basic needs would force
organisms to compete for
resources.
•The struggle for existence means
that members of each species
compete regularly to obtain food,
living space, and other necessities
of life.
•The ability of an individual to
survive and reproduce in its
specific environment is fitness.
•Darwin proposed that fitness is the
result of adaptations.
•An adaptation is any inherited
characteristic that increases an
organism's chance of survival.
•Successful adaptations enable
organisms to become better
suited to their environment and
better able to survive and
reproduce.
•Individuals with characteristics that
are not well suited to their
environment either die or leave
few offspring.
•Darwin called this process survival
of the fittest.
•Because of its similarities to artificial
selection, Darwin referred to the
survival of the fittest as natural
selection.
•The traits being selected
contribute to an organism's fitness
in its environment.
•Over time, individuals with a
greater fitness will survive and
reproduce at a higher rate that
individuals with inferior traits or
behaviors.
• This results in more individuals with
an better fitness to build in the
population.
•Some types of adaptations are
camouflage, blending into the
environment so the creature is not
seen.
Stick Mantid
Flower Mantid
•Mimicry- evolved to look like
another creature that is much
more dangerous.
Coral Snake
(Poisonous)
Milk Snake
(Not poisonous)
Descent With Modification
•Each living species has
descended, with changes, from
other species over time.
•Darwin referred to this principle as
descent with modification.
•Descent with modification implies
that all living organisms are related
to one another.
•This is the principle known as
common descent.
–An individuals ability to survive
and reproduce in a given
environment is its
•evolution.
•fitness.
•camoflague.
•Artificial selection
– Which of the following is not a part of
Darwin’s idea of natural selection
•Individuals within the population is
genetically different
•Individuals within the population
must compete for resources to
survive
•A population produces more
offspring than can survive
•The weak and unhealthy should
have an equal chance to survive
–When humans select which traits
are beneficial in another species
like dogs, horses, and pigs is
called
•Natural selection
•Artificial selection
•Fitness
•Mimicry
–Darwin theorized that all species
are related to each other, they
just evolved differently over time.
This idea is called
•Convergent evolution
•Artificial selection
•Common descent
•Acquired characteristics
– Which of the statements below
would be consistent with Darwin’s
ideas of evolution?
•Evolution attempts to develop
perfect species that will survive for
all time
•Populations evolve better with less
variation
•Evolution is a rapid process that
happens in a short amount of time
•Individuals with better adaptations
survive and reproduce at higher
rates
Evidence for Evolution
•Darwin argued that living things
have been evolving on Earth for
millions of years. Evidence for this
process could be found in the fossil
record, the geographical
distribution of living species,
homologous structures of living
organisms, and similarities in early
development, or embryology.
The Fossil Record
•Darwin saw fossils as a record of
the history of life on Earth.
•By comparing fossils from older
rock layers with fossils from
younger layers, scientists could
document that life on Earth has
changed over time.
Archaeopteryx
Biogeography
•Organisms are uniquely adapted
to the environments or habitats in
which they live.
•The same types of organisms
evolve independently based on
the environmental pressure of their
habitat.
Biogeography in fossils
Homologous Body Structures
•Structures that have different
mature forms but develop from
the same embryonic tissues are
called homologous structures.
•Similarities and differences in
homologous structures help
biologists group animals according
to how recently they last shared a
common ancestor.
• Not all homologous structures serve
important functions.
• The organs of many animals are so
reduced in size that they are just
vestiges, or traces, of homologous
organs in other species.
• These organs are called vestigial
organs.
Embryology
•The early stages, or embryos, of
many animals with backbones are
very similar.
•The same groups of embryonic
cells develop in the same order
and in similar patterns to produce
the tissues and organs of all
vertebrates.
1
2
3
4
5
6
7
Which embryo is the human,
Cat, chick, rabbit, fish,
salamander, pig, and tortoise?
8
Biochemical Evidence
•Almost all living organisms use the
same basic biochemical
molecules for life.
–DNA (genetic material)
–ATP (cellular energy source)
–Enzymes (proteins to control
chemical reactions.
•Many similarities found in the
genes and DNA sequences of
completely different organisms.
•Human DNA and chimpanzee
DNA is 98.77% identical in their
base pairing.
•Human DNA is more similar to
other mammals than it is to
reptiles, birds or fish.
•Biologists compare the amino acid
sequences of common proteins in
different life forms.
•Similarities in amino acids is
consistent with the idea of
common descent by evolutionary
theory.
Similarities
in
Hemoglobin,
protein in
blood cells
Similarities in Cytochrome c, protein found in
the mitochondria. Helps in energy production
–The body parts found in different
species that have the same
basic structure are
•Homologous structures.
•Vestigial organs.
•Caused by random chance.
•Shows evidence that each
species are not related to each
other
–To show how the bones and
body designs of species have
evolved over the ages, scientists
study
•DNA and RNA
•The rock layers in the Earth
•The fossils of the different
species
•Only modern living species
–
Which are used to show evidence
that supports the theory that
species have evolved over time
I. Fossils
II. Embryos
III. DNA of different species
•
•
•
•
I only
I and III only
I and II only
I, II and III
Summary of Darwin's Theory
• Individual organisms differ, and
some of this variation is heritable.
• Organisms produce more offspring
than can survive, and many that
do survive do not reproduce.
• Because more organisms are
produced than can survive, they
compete for limited resources.
•Individuals best suited to their
environment survive and
reproduce most successfully.
•These organisms pass their
heritable traits to their offspring.
Other individuals die or leave
fewer offspring.
•This process of natural selection
causes species to change over
time.
•Species alive today are
descended with modification from
ancestral species that lived in the
distant past.
•This process, by which diverse
species evolved from common
ancestors, unites all organisms on
Earth into a single tree of life.
Where does the variation
come from?
•Each individual has its own set of
instructions on how to build the
creature (DNA).
Where does the variation
come from?
•DNA is made of individual genes
(small sections of DNA that are the
instructions for a specific part of
the body or protein)
•If DNA was a recipe book, a gene
would be a recipe.
•Many genes have at least two
forms, or alleles.
•Genetic variation is studied in
populations.
•A population is a group of
individuals of the same species
that interbreed.
•A gene pool consists of all genes,
including all the different alleles,
that are present in a population.
•The relative frequency of an allele
is the number of times the allele
occurs in a gene pool, compared
with the number of times other
alleles for the same gene occur.
•Relative frequency is often
expressed as a percentage.
•In genetic terms, evolution is any
change in the relative frequency
of alleles in a population.
•The two main sources of genetic
variation are mutations and the
genetic shuffling that results from
sexual reproduction.
Mutations are RANDOM changes in
the DNA that can cause changes in
the genes (instructions to build the
body)
Where does the variation
come from?
•Most mutations have no effect on
the individual or are harmful.
•A small number of mutations might
be beneficial to the organism.
Where does the variation
come from?
•If the mutation results in a change
to a body part that helps the
creature to survive and then
reproduce, the change would be
called an Adaptation.
•Mutations can only change or
alter existing traits, they do not
create new traits.
Where does the variation
come from?
•During the process of sexual
reproduction, one set of DNA
comes from each parent (in the
sperm and eggs) to create an
new unique set of instructions or
combination of genes.
Where does the variation
come from?
•Each time the sperm and eggs are
made, the instructions are altered
slightly to allow for variations or
slight differences.
•This way, siblings will always have
slightly different combinations of
genes, even though they have the
same parents.
Importance of Variation
•Variation is essential for the
continued survival of life on the
planet.
•Living things adapt to changes in
the environment.
•This environmental pressure is what
helps to determine a creature’s
fitness.
•If the environmental conditions
change, variations between
individuals and between species
helps to ensure that some will have
beneficial traits.
•Even alleles that were harmful in
one environment, may become
beneficial in the changing
environment.
•Alleles that cause a rabbit to have
larger than normal ears that lives in
the snow is at a disadvantage. It
loses too much heat.
•But if the environment changes,
warming the air, the larger ears
are beneficial to keep the rabbit
cooler.
•Some environmental changes
may be so severe, that whole
species die off, goes extinct.
•By having variation between the
different species allows for the
possibility that some of the species
survive and repopulate the
environment.
•When dinosaurs went extinct, a
few small mammals and small
reptiles survived to repopulate the
environment.
•Natural selection affects which
individuals survive and reproduce
and which do not.
•If an individual dies without
reproducing, it does not contribute
its alleles to the population’s gene
pool.
•If an individual produces many
offspring, its alleles stay in the gene
pool and may increase in
frequency.
•Peppered moths live on the trees
found in England.
•There are two main alleles for
peppered moths
–White
–Black
•The trees the moths would live on
had white bark.
•Birds catch moths they can see.
•Which moth was best adapted?
Which allele would have
the highest frequency in
the population?
White Allele
•Over time,
pollution stained
the bark of the
trees, making
them dark.
•Which allele has
the advantage?
•What happened
the frequency of
the dark allele?
•The trait or adaptation that
enables an organism to be
successful is a function of its
phenotype, physical
characteristics.
•Evolution only selects which
phenotypes are favorable.
•The phenotype is determined by
the genotype, alleles found in the
genes.
•The genotypes of beneficial
phenotypes build in the gene
pool, change the gene frequency.
•Individuals with poor phenotypes,
thick black fur in a desert
environment, will not be as
successful in passing on their
genotypes.
•The alleles for harmful traits will
reduce in frequency in the gene
pool, but will not disappear.
•Even alleles that are lethal, cause
death, are not completely
eliminated from the gene pool.
•A homozygous recessive (aa)
genotype may be lethal, killing the
individual early in life, like TaySachs disorder.
•But a recessive allele can still be
passed down generation after
generation in heterozygous
genotypes (Aa)
•Sickle cell anemia is a
homozygous recessive disorder,
but the allele continues to be
passed down in heterozygous
individuals that have a normal
phenotype.
•Normal blood cells are round,
fitting easily through blood vessels.
•Sickle cells, get stuck in smaller
blood vessels, causing infections
Normal
phenotype
Sickle cell
phenotype
•Evolution is any change over time
in the relative frequencies of
alleles in a population.
•Populations, not individual
organisms, can evolve over time.
•For example, a lizard population is
normally brown, but has mutations
that produce red and black forms.
•Red lizards are more visible to
predators, so they will be less likely
to survive and reproduce.
Therefore, the allele for red color
will become rare.
•Black lizards may warm up faster
on cold days. This may give them
energy to avoid predators better
than even the brown lizards. In
turn, they may produce more
offspring.
•The allele for black color will
increase in relative frequency.
•Black and red are both changes in
phenotype
–Natural selection causes
•The frequency of alleles to
remain the same
•An individual to evolve to a
new environment.
•the change in a species due to
changes in the gene pool
•The population to remain
unchanging for as long as
possible
–The amount of alleles for a
specific trait found in the gene
pool is the
•The frequency of alleles
•Genetic drift
•Common descent
•Gene flow
–Which statement is true
regarding mutations
•Mutations have no effect on
the frequency of alleles
•Most mutations have no effect
on an individual
•Mutations are unable to
change the gene pool
•No mutations can be
beneficial to an individual.
Genetic Drift
•A random change in allele
frequency is called genetic drift.
•In small populations, individuals
that carry a particular allele may
leave more descendants than
other individuals do, just by
chance.
•Over time, a series of chance
occurrences of this type can
cause an allele to become
common in a population.
•Genetic drift may occur when a
small group of individuals colonizes
a new habitat.
•Individuals may carry alleles in
different relative frequencies than
did the larger population from
which they came.
•The new population will be
genetically different from the
parent population.
•Descendants
Population A
Population B
Founders Effect
•When allele frequencies change
due to migration of a small
subgroup of a population it is
known as the founder effect.
• Some remote villages, polydactyl is
common because the trait was in
founding members.
Bottleneck effect
•When allele frequencies change
due to the random removal of
alleles in the gene pool is the
bottleneck effect.
Variation leads to Speciation
•Since each individual in a species
is attempting to survive (not be
killed), they develop different ways
to survive based on their
adaptations.
•As different adaptations build in a
population, it leads to the
development of new species.
•This is Speciation
•A species is a group of organisms
that breed with one another and
produce fertile offspring.
•The gene pools of two populations
must become separated for them
to become new species.
•As new species evolve,
populations become
reproductively isolated from each
other.
•When the members of two
populations cannot interbreed
and produce fertile offspring,
reproductive isolation has
occurred.
•Reproductive isolation can
develop in a variety of ways,
including:
•behavioral isolation
•geographic isolation
•temporal isolation
•Behavioral isolation occurs when
two populations are capable of
interbreeding but have differences
in courtship rituals or other
reproductive strategies that
involve behavior.
Blue-footed
boobies display
their blue feet
when courting
potential
mates.
Red-footed boobies are not
impressed by the display.
•Geographic isolation occurs when
two populations are separated by
geographic barriers such as rivers
or mountains.
•Geographic barriers do not
guarantee the formation of new
species.
•If two formerly separated
populations can still interbreed,
they remain a single species.
•Potential geographic barriers may
separate certain types of
organisms but not others.
•Temporal isolation occurs when
two or more species reproduce at
different times or seasons.
–When two species do not
reproduce because of
differences in mating rituals, the
situation is referred to as
•temporal isolation.
•geographic isolation.
•behavioral isolation.
•reproductive isolation.
– Lethal diseases continue to be
passed on through the population
generation after generation
because the alleles
•Are mutations and don’t affect
most individuals.
•Are dominant and easy for an
individual to avoid.
•Because they are passed on only
by homozygous individuals.
•Can be passed on by heterzygous
individuals, since they don’t suffer
from the trait.
–The most important factor
involved in the evolution of the
different species that reproduce
during different times of the year
is
•temporal isolation.
•geographic isolation.
•behavioral isolation.
•different food sources.
–All of the following played a role
in speciation of Galápagos
finches EXCEPT
•natural selection.
•Geographic isolation.
•reproductive isolation.
•no changes in the gene pool.
–When a new species evolves
because members of the
population be breading during
differnet seasons, is an example
of
•Geographic isoltion.
•Genetic isolation.
•Behavioral isolation.
•Reproductive isolation.
Diversity of Life
•Evolution and speciation has
produced the vast diversity seen
on Earth.
•Life originated on Earth 3.8 Billion
Years Ago.
•The first life forms were Bacteria,
simple single celled creatures.
•Bacteria were the only living things
for more than 2 billion years
Diversity of Life
•These cells evolved into more
complex multicellular cells, the first
animals and plants.
Diversity of Life
•Over the ages, life evolved into
many new species as the
environment changed.
•Evidence of these ancient forms of
life are found in Fossils.
•Fossils are any remains of living
things that were trapped in the
Earth and kept from
decomposing. (Bones, teeth,
footprints, dung, amber)
What Fossils Tell
•Most fossils are found in
sedimentary rock.
•Sedimentary rock is layers of dirt,
small rocks and other materials,
that are smashed together for long
periods of time until the fuse.
What Fossils Tell
•If an animal or plant is trapped in
these layers of dirt and rock, their
bodies may be preserved and
turned into a fossil.
•As more layers of dirt pile up
above, sedimentary rock forms
distinct layers.
•The deeper a fossil is in the rock,
the older it is.
•The higher it is in the rock, the
younger it is.
•Determining the age of a fossil by
looking at what rock layer it is in is
Relative dating.
•Relative dating does not give an
exact age of the fossil, only
determines if it is older than or
younger than another fossil.
•To determine the actual age of a
fossil, Absolute dating is used.
•Absolute dating measures the
amount of radioactive atoms
found in the fossil or layer of rock
the fossil is in.
•Scientists are then able to
determine the actual age of the
rock.
Rates of Decay
Parent
Uranium 238 Lead 206
Half- life
(years)
4.5 Billion
Uranium 235 Lead 207
704 Million
Potassium 40 Argon 40
1.25 Billion
Carbon 14
Daughter
Nitrogen 14 5730 years
Diversity Helps Survival
•Fossils show the great diversity of
life from the past.
•It was through this great diversity
that has allowed life to continue
even after mass extinctions.
Mass Extinctions
•Mass extinctions are when a large
number of species die off from the
planet, never to return.
•The Permian mass extinction
resulted in 90%-95% of all marine
species and 70% of terrestrial
species to go extinct
•The Cretaceous extinction caused
18% of terrestrial vertebrates to go
extinct (including dinosaurs)
Mass Extinctions
•Most mass extinctions are caused
by dramatic changes in the
environment.
•The greater the diversity of life, the
better the chance that some life
forms will survive the change and
adapt to the changing
environment.
– Which is correct that it allows life to
continue when there is a dramatic
change to the environment
•A greater amount of biodiversity in
the environment
•A larger population with less
variation
•A smaller amount of biodiversity
but with a large population size
•A lower frequency of alleles in the
gene pool
– Which best describes genetic drift
•When the frequency of alleles
changes because of natural
selection
•When the frequency of alleles
changes because of random
chance
•When there is a large amount of
sexual reproduction
•A lower frequency of alleles due to
mutations
– A scientist determines that a mass
extinction occurred in the past. Which
type of evidence would support this
hypothesis?
•Many fossils of the same species found
in the same layers of sedimentary rock
•Many fossils of a variety of different
species found in the same layers of
sedimentary rock
•The same type of fossil found in many
different layers of sedimentary rock
•Mass extinctions can not be
determined by fossils