Transcript ď - Sites

Notes #1
Patterns, Processes, & Rates of
Evolution
 Adaptations
are traits that help living
organisms survive.
 Different organisms in a species have
different traits. These differences are
called variations.
How do variations occur?
 Mutations
 Rearrangement
of genetic material during
sexual reproduction
Mutation
 Can
be helpful, harmful, or have no effect
at all.
 If an organism’s environment changes and
it happens to have a mutation (adaptation)
which allows it to survive in its new
environment, it will.
 If not, it will die.
Draw this diagram
Speciation

Remember: A species is a group of organisms that share
similar characteristics & can interbreed to produce fertile
offspring.
 Remember: All the members of a species that live in an
area at the same time make up a population.
 Over time, variations that arise within a population as a
result of natural selection can have two major outcomes:
speciation or extinction.
 Speciation is the evolution of a new species from an
existing species.
 One species can evolve into another if the environment
changes.
Examples of Speciation



If the environment becomes colder, animals with the
inherited trait for thicker fur would be better to survive,
reproduce, & pass this trait on to their offspring.
If a new predator moves into an area, the organisms it
preys on that have longer legs to help them escape the
predator are more likely to survive and reproduce.
Land of Whoa~~Storytime! So listen up!
Events that can lead to speciation
 A barrier
forms that separates numbers of
a species; this is called geographical
isolation
 Two groups are in different environments
 Groups begin to show different traits as a
result of natural selection; this is called
divergent evolution
GEOGRAPHIC ISOLATION
 OCCURS
WHEN A POPULATION
BECOMES SEPARATED BY CHANGES
IN THE ENVIRONMENT.
 AFTER SEVERAL GENERATIONS,
ISOLATED ORGANISMS MAY CHANGE
ENOUGH TO FORM A NEW SPECIES
Mechanisms of Evolution through
genetic variation
 Mutations
 Caused
by errors during DNA replication
or by damage to DNA from environmental
factors such as radiation.
 To affect evolution, mutations must be
passed from one generation to the next.
 Only mutations in gametes can be passed
to offspring & have the potential to affect
evolution.
Mechanisms of Evolution through
genetic variation
Gene flow – the introduction of genes from one
population into the gene pool of another
population
 Gene pool- combined genetic information of all
members of a population
 The most significant factor that affect gene flow
is mobility (movement).
 For example, animals are more mobile than
plants & tend to have a higher rate of gene flow.

Rates of Evolution
 Two
main views: gradualism & punctuated
equilibrium
Rates of Evolution:
Gradualism
 Theory
that evolution occurs over a long
period of time.
 Change is slow & constant.
 This is how Darwin thought natural
selection worked.
Rates of Evolution:
Punctuated Equilibrium


Theory states that evolution occurs in spurts.
A period of rapid speciation will be followed by a
long period of time in which little or no change
occurs.
 Supporters of this theory believe that the periods
of rapid change are caused by either random
changes in DNA or large, sudden changes in the
environment.
 Scientists who favor punctuated equilibrium
theory often point to the Cambrian explosion to
support their views.
Cambrian Explosion
 Period
of geologic time, about 530 million
years ago, when most of the major groups
of complex animals appeared on Earth.
 Fossil record shows few fossils before this
time. Mostly of simple organisms.
 During the Cambrian explosion, a much
larger number of fossils of more complex
animals appeared in a short time.
Extinction
 Permanent
loss of a species
 Can happen slowly as populations fail to
adapt in the environment die without
producing offspring or produce fewer
offspring in each generation.
 Quickly by Mass extinction – loss of huge
numbers of species in a fairly short period
of time
Examples of Mass Extinctions
 Occurred
at the end of the Permian period
 About 250 million years ago
 96% of all ocean invertebrates became
extinct
Examples of Mass Extinctions
 Occurred
at the end of the Cretaceous
period
 Killed 60-75% of ocean species
 Dinosaurs

Mass extinctions make it possible for new species to
evolve and thrive.
QUIZ TIME!
 1.
The evolution of a new species from an
existing species is called
 a. mass extinction
c. biodiversity
 b. speciation
d. gradualism
 2.
Gradualism is the theory that evolution
occurs over a _______________ period of
time.
 a. short
b. long
#3
Which of the following best describes the theory of
punctuated equilibrium?
a. Biological change occurs slowly and steadily over a
long period of time.
b. Biological change occurs quickly over a short period
of time and is followed by long periods of little or no
change.
c. Tiny changes in a species add up to major changes
over time.
d. Events throughout the history of life have caused the
extinction of species.
 4.
Earth has experienced several ice ages.
Which type of organisms would natural
selection favor if Earth had another ice
age?
 a. organisms that swim
 b. organisms that are predators
 c. organisms that carry out photosynthesis
 d. organisms adapted for surviving cold
temperatures
Checks Your Answers
 1.
b
 2. b
 3. b
 4. d