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Evolution and Natural Selection
How life has changed on Earth.
The Theory of Evolution
The evolution of a species is the result of an individual organism struggling to survive in a given environment.
A scientific
is a
of phenomena that have occurred in the natural world.
There has been no credible evidence presented to disprove evolution
Individuals with the
will have the best
chance to survive.
The individuals that
then have the chance to
to their offspring.
Charles
was the first person to successfully describe the process of evolution, which he titled, “
”
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
That hypothesis has become the theory of evolution.
Darwin collected the preserved remains of ancient organisms, called
.
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.
1
2
3
4
Natural Selection
- 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
each year
- Each of the babies that are produced by the parents will be a little bit
.
There will be slight changes in
, etc.
- each individual that is produced
. It will compete with its own species and other species to survive.
and water, Avoiding
Attracting
,
, Obtaining shelter or a territory
- The individuals with the
and have the opportunity to
to its offspring.
Evolution occurs when these
over many
generations and the
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 is the selection by humans for
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
and a shortage of life's basic needs would
force organisms to
.
The
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
.
Darwin proposed that
.
An
is any inherited characteristic that
organism's
an
.
enable organisms to become better suited to their
environment and better able to
.
Individuals with characteristics that are not well suited to their environment either
Darwin called this process
.
Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as
The traits being selected contribute to an organism's
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
in the population.
Some types of adaptations are
, blending into the environment so the creature is not
seen.
- evolved to look like another creature that is much more dangerous.
Descent With Modification
Each living species has
,
with changes, from other species over time.
Darwin referred to this principle as
Descent with modification implies that
to one
another.
This is the principle known as
.
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
, the
of living species,
of living organisms, and similarities in early development, or
.
The Fossil Record
Darwin saw
as a record of
the
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.
Biogeography
Organisms are uniquely adapted to the environments or
habitats in which they live.
The same types of organisms
.
Homologous Body Structures
Structures that have
but develop from the same embryonic tissues are
called
.
Similarities and differences in homologous structures help biologists
group animals according to how recently they last
.
Not all homologous structures serve important functions.
The organs of many animals are so
that they are just
, of homologous organs in other species.
These organs are called
.
Embryology
The early stages, or
, 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.
Biochemical Evidence
Almost all living organisms use the same basic biochemical molecules for life.
Many similarities found in the
genes and DNA sequences of
completely different organisms.
Human DNA and chimpanzee
DNA is
identical in their base
pairing.
Human DNA is more similar to
other mammals than it is to
reptiles, birds or fish.
Biologists
of common proteins in different life forms.
Similarities in amino acids is consistent with the idea of common descent by evolutionary theory.
Summary of Darwin's Theory
Individual organisms differ, and some of this variation is heritable.
Organisms produce
, and many that do survive do not reproduce.
Because more organisms are produced than can survive, they
.
Individuals best suited to their environment survive and reproduce
.
These organisms
. Other individuals
die or leave fewer offspring.
This process of natural selection causes
.
Species alive today are
from ancestral species that lived in the distant
past.
This process, by which diverse species evolved from common ancestors,
on Earth into a single tree of life.
Where does the variation come from?
Each individual has its own set of
on how to build the creature
DNA is made of individual
(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
.
is studied in populations.
A
A
alleles, that are
is a group of individuals of the same species that interbreed.
consists of
, including all the different
.
The
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
.
In genetic terms, evolution is any change in the relative
in a population.
The two main sources of genetic variation are
and the genetic shuffling that results from
Mutations are
that can cause changes in
the genes (instructions to build the body)
Most mutations have
on the individual or are
A small number of mutations might be
.
to the organism.
If the mutation results in a change to a body part that helps the creature to
the change would be called an
,
.
Mutations can only
existing traits, they
During the process of
new traits.
, one set of DNA comes from each parent (in the
) to create an new unique set of instructions or combination of genes.
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
,
even though they have the same parents.
Importance of Variation
is essential for the continued
survival of life on the planet.
Living things adapt to changes in the environment.
This
is
what helps to determine a creature’s fitness.
If the environmental conditions change, variations between individuals
and between species help to ensure that some will have beneficial traits.
Even
in
one environment,
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
By having
species
.
between the different species allows for the possibility that some of the
the environment.
When dinosaurs went extinct, a few small mammals and small reptiles survived to repopulate the environment.
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
.
If an individual produces many offspring, its
.
stay in the gene pool and may
Peppered moths live on the trees found in England.
There are two main alleles for peppered moths
1
2
The trees the moths would live on had white bark.
Birds catch moths they can see.
Which moth was best adapted?
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
.
Evolution only selects which
.
The phenotype is determined by the
.
The
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
`
in the gene pool, but will not disappear.
Even alleles that are
, are not completely eliminated from the gene pool.
A
) genotype may be
,
killing the individual early in life, like Tay-Sachs disorder.
But a recessive allele can still be passed down generation after generation in
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
Evolution is any change over time in the relative
in a population.
, not individual organisms, can
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
Genetic Drift
A random change in allele frequency is called
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
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.
.
Founders Effect
When allele frequencies change due to
of a population it
is known as the
.
Some remote villages, polydactyl is common because the trait
was in founding members.
Bottleneck effect
When allele frequencies change due to the
in the gene pool is the
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
, it leads to the development of new species.
This is
A
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
from each other.
When the members of two populations
and produce fertile offspring,
reproductive isolation has occurred.
Reproductive isolation can develop in a variety of ways, including:
1
2
3
occurs when two populations are capable of interbreeding but have
differences in
or other reproductive strategies that involve behavior.
occurs when two populations are separated by
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.
occurs when two or more species
.
Evolution and speciation has produced the vast diversity seen on Earth.
Life originated on Earth
.
The first life forms were
, simple single celled creatures.
Bacteria were the only living things for more than
years
These cells evolved into more
, the first animals and plants.
Over the ages, life evolved into many new species as the environment changed.
Evidence of these ancient forms of life is found in
.
Fossils are any
that were trapped in the Earth and kept from
decomposing.
What Fossils Tell
Most fossils are found in
.
Sedimentary rock is
and other materials, that are smashed together for
long periods of time until the fuse.
If an animal or plant is trapped in these layers of dirt and rock, their
and
turned into a fossil.
As more layers of dirt pile up above, sedimentary rock forms distinct
layers.
.
Determining the age of a fossil by looking at what rock layer it is in
is
.
Relative dating does
of the fossil, only determines if it is older than or younger than another fossil.
To determine the actual age of a fossil,
is used.
Absolute dating measures the amount
found in the fossil or layer of rock the fossil is in.
Scientists are then able to determine the actual age of the rock.
Diversity Helps Survival
Fossils show the great diversity of life from the past.
It was through this great
that has allowed
even after mass extinctions.
Mass Extinctions
are
when a
from the planet, never to return.
The Permian mass extinction resulted in
of all marine species and
to go extinct
The Cretaceous extinction caused 18% of terrestrial
vertebrates to go extinct (including dinosaurs)
Most mass extinctions are caused by
.
The
of life, the better the chance that some life forms will
to the changing environment.