Download Theory of Evolution

•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 Peru.
Within the island
chain there was
significant
differences
between 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, living space, and
other necessities. In natural selection, those variations in the
genotype that increase an organism’s chances of survival and
reproduction are preserved and multiplied from generation to
generation.
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.
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
.
share a common pool of genes aka: Gene Pool
Gene pools
consist of all genes, 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/Diversifying 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.
Patterns and Processes
of Evolution
Evidence shows that evolution has often developed at different
rates for different organisms at different times over the long
history of life on Earth.
Gradualism: Gradualism is the
concept that organisms evolve in
a slow and steady manner and
acquire changes over long
periods of time.
Punctuated Equilibrium is term
used to describe rapid periods of
change that occur in a relatively
short period of time (remember a
short period of geologic time could
be thousands of years).
Patterns of evolution become evident when fossil records and
Two patterns of
evolution that we will cover
include Adaptive Radiation and
Convergent Evolution.
observations are analyzed.
Adaptive radiation-Divergent
Evolution ordinarily involves the
development of new species in
the new environments from a
common ancestor.
The most common situations
which result in adaptive radiation occur following mass
extinctions, or when species move into new, unoccupied regions.
Convergent evolution
In evolutionary biology,
convergent evolution is the
process whereby organisms not
closely related, independently
evolve similar traits as a result
of having to adapt to similar
environments or ecological niches.
Coevolution: Coevolution is a
change in the genetic
composition of one species (or
group) in response to a genetic
change in another. The classic analogy is
the coevolutionary arms race: a plant has chemical
defenses, an insect evolves the biochemistry to detoxify
these compounds, the plant in turn evolves new defenses
that the insect in turn "needs" to further detoxify.
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.
2.) Fossil Records: Many recently discovered fossils form
a series that traces the evolution from modern species to
extinct descendants.
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.
Homologous traits have similar structure and similar function.
Darwin also noticed the presence of analogous traits
.
Analogous traits are traits that have similar function but
completely different structure.
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.