Download •The Earth has millions of organisms that display different

•The Earth has millions of organisms that display different
characteristics and traits. This variety of living things is called
biological diversity. How did all of these different organisms
arise? How are they related? The Evolutionary Theory explains
these questions by using observations, scientific facts, and
hypotheses.
Evolution, or change over time, is the process by which
modern organisms have descended from ancient organism. A
theory is a well supported testable explanation of phenomena
that have occurred in the natural world.
Charles Darwin
Charles Darwin was one of the first scientists to develop
a theory of evolution. His theory was based on
observations he made while sailing around the world in
1831 on the H.M.S Beagle.
Darwin noticed that when he visisted different
geographical locations he saw similar species. Even though
many of these locations were separted by long distances
organisms that lived in similar environments had similar
characteristics.
Darwin also noticed that some environments, like
Australia, had unique organisms that were found nowhere else in the world.
Darwin also examined fossils and found that some extinct organisms were
similar to living species.
One of the focal points of his journey was the Galapagos Islands
off the west coast of South America.
The Galapagos Islands at the
time were fairly isolated from
the mainland of Ecuador and
Within
the island
chain there
was
significant
differences
between
Peru.
each island.
Hood Island, for example, had
sparse vegetation and was
extremely hot. Isabela Island
had rich vegetation that
animals could easily reach.
Darwin noticed that animals on each of the Islands were well
suited to survive and flourish according to the conditions on that
specific island. Some animals were similar, but they occupied
different habitats on one island.
These observations started his thinking toward how these animals
became so well adapted.
The central theme in
Darwin’s theory of
evolution is the concept
of natural selection
.
Natural
selection deals with an organism struggle for existence, meaning
that members of each species compete regularly to obtain food,
The ability
of an individual to survive
and reproduce in its
specific environment is
called fitness. An
adaptation is any
characteristic that
increases an organism’s
chance of survival or
reproduction
living space, and other necessities.
.
The struggle for existence, fitness, and adaptation lead to the
concept of survival of the fittest.
Over time,
natural selection results
in changes in the
inherited characteristics
of a species’ fitness in
its environment.
Great White Shark
Giant Anteater
How have these animal adapted to their environment, or changed
over time to become successful?
Darwin’s Theory of Evolution
can be summarized.
1. Individual organisms in nature
differ from one another. Some of this
variation is inherited.
2. Organisms in nature produce
more offspring than can survive,
and many of those that survive do not reproduce.
3. Because more organisms are produced that can survive,
members of each species must compete for limited
resources.
4. Because each organism is unique, each has different
advantages and disadvantages in the struggle for
existence.
5. Individuals best suited to their environment survive
and reproduce most successfully. The characteristics
that make them best suited to their environment are
passed down to the offspring.
6. Species change over time. Over long periods of time
natural selection causes changes in the characteristics of
species.
7. Species alive today have descended with modifications
from species that lived in the past.
8. All organisms on Earth are united into a single tree of
life by common descent.
•The formation of a new species is called speciation. Recall that
biologists define a species as a group of organisms that breed
with one another and produce fertile offspring. This means that
individuals in the same species share common traits. If those
traits increase fitness, than the traits will eventually be found
throughout the population.
Genes lead to Speciation and
Evolution
New species form due to the genetic variation in the entire
population. Members of the same population interbreed so they
. Gene
pools consist of all genes,
share a common pool of genes aka: Gene Pool
including all the
different alleles for each
gene that are present in
a population.
Allele frequency is the
number of times an allele
occurs in a gene pool, compared
to the total number of alleles in that pool for the same
gene.
As allele frequencies change the overall population may start to look
a little different. A few different types of scenarios may start to occur
Directional Selection
One phenotype (appearance) is more favorable
Example is the industrial melanism in moths during the
industrial revolution
.
Stabilizing Selection
The "in between" phenotype is the best.
Example is birth weigh between 6 and 9 pounds
Disruptive Selection
The "in between" is less common.
•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. The
sharks above are related but unable to mate and produce
offspring therefore they are members of two different species.
Reproductive isolation can develop in a variety of ways
including behavioral isolation, geographic isolation, and
temporal isolation.
Behavioral isolation: occurs when two populations are
capable of interbreeding but have differences in
courtship rituals or other behaviors.
Geographic isolation:
occurs when populations
are separated by
geographic barriers such
as rivers, mountains, or
bodies of water.
Temporal isolation: occurs when two or more species
reproduce at different times. For example, three similar
species of orchid all live in the some rain forest, and they all
reproduce at different times of the year.
Speciation in Darwin’s Finches
•Speciation in the Galapagos finches occurred by founding of a
new population, geographic isolation, changes in the new
population’s genes, reproductive isolation, and ecological
competition.
1.) Founders Arrive: Many years
ago, a few finches from the
mainland of South America arrived
on one of the Galapagos Islands.
These birds may have gotten lost or
were blown off course by a storm
when flying. They managed to
survive on the island.
2.) Separation of Populations:
Later on, some birds from Species
A crossed to another island in the
Galapagos chain. These birds do
not usually fly over open water
therefore the birds on the two
islands were isolated from each
other.
4.) Reproductive isolation: The
two populations change some much
over time that if birds from island
B went back to island A they would
not mate with the island A birds.
This is reproductive isolation, and
the formation of two different
species, A and B.
3.) Changes in the Genes: Over
time the two populations on the
different islands adapted to their
local environments. Each island
offered different food sources and
over this long period of time the
Finches evolved differently to deal
with this.
.
As the finches competed for food and space there was more
migration and speciation until multiple species of finches existed.
Today there 13 different species of finches on the Galapagos
Islands.
1.) Biogeography: Patterns in the
distribution of living and fossil
species tell us how modern
organisms evolved from their
ancestors.
Darwin noticed two things, first, closely related species
differentiate (change) in different environments. The second
pattern he noticed was that very distantly related organisms
developed similar traits when they were in the same environment.
Fossil Records: Many
recently discovered
fossils form a series that
traces the evolution from
modern species to
extinct descendants.
2.)
3. Comparing Anatomy: Darwin
suggested that animals with similar
structures evolved from a common
ancestor with a basic version of
that structure.
Structures that are shared by
related species are called
homologous structures. Homologous
structures adapted to different purposes as the result of decent
with modification.
.
Analogous traits are traits that
have similar function but
completely different structure.
Darwin also noticed the presence of analogous traits
4.) Genetic and Molecular Biology: Genetic research has allowed
us to determine that many organisms have multiple genes in
common, for example, cytochrome C. The more genes that two
organisms have in common the closer they are on the evolutionary
tree.