Transcript Evolution Part 1

The Theory of Evolution
In science, theories are statements or models that have
been tested and confirmed many times.
Theories have some important properties:
•They explain a wide variety of data and observations
•They can be used to make predictions
•They are not absolute
•They serve as a model of understanding the world
and can be changed as the world view changes
The Theory of Evolution is considered
a Unifying Theory of Biology, because
it answers many of these questions and
offers an explanation for the data.
How does evolution explain the
origin and development of
species?
The Beginning of the Story
Evolution begins with variation.
NO VARIATION = NO EVOLUTION
What causes variation?
What causes variation?
1. List 5 types of variation.
2. List 3 things that can cause variation in an
organism?
3. Write them on your clear board.
4. Transfer them into your notes.
In the real world, how do mutations
come about?
1. Internal
1. Replication errors
2. High energy molecules generated within the
organism – free radicals.
2. External
1. Chemicals, i.e. mutagens
2. Radiation, e.g. UV, cosmic rays
See video.
Mutations may:
A.
B.
C.
D.
Have positive effects
Have negative effects
Have no effect
All of the above
All of the following can be causes of
mutation except:
A.
B.
C.
D.
Mutagenic chemicals
An organism’s need to be successful
Radiation from the sun
Free radicals
Whether a mutation is positive or
negative depends the location of the
mutation in the genome:
True
False
Whether a mutation is positive or
negative depends on the environment
of the organism.
True
False
Which of the following statements is
false:
A. Mutations occur all the time.
B. Everyone has mutations.
C. Mutations always lead to a decrease in
success of the organism.
D. Mutations can be caused by a variety of
factors.
Tracking Mutations
• Mutations occurring in the genes of the
gametes are inherited by offspring.
• These mutations may show up through
thousands of generations as the same
chromosome is transmitted from parent to
child.
• Understanding these mutations can tell us a lot
about the ancestry of organisms including
humans.
What specific name do we have for
inherited mutations?
A.
B.
C.
D.
Chromosomes
Markers
Genes
Gametes
What genetic material does a man
always inherit?
A)
B)
C)
D)
His mother’s paternal chromosomes
His father’s paternal chromosomes
His father’s Y chromosome
All of his fathers chromosomes
What is the name of the people the
scientist is investigating?
A.
B.
C.
D.
Koi San
Africans
Kenyans
Aborigines
Why is Dr. Wells so interested in
these bushmen?
A. He thinks they may have some special
genes that can be used in medicine.
B. He thinks they may be the group most
closely related to our ancestors who left
Africa.
C. He thinks they may have invented the bow
and arrow.
D. He thinks they may have invented spoken
language.
Meiosis and fertilization allow for great
diversity in sexual species compared to
asexual species.
In evolutionary terms, sex is more important
than life itself. Sex fuels evolutionary change
by adding variation to the gene pool. The
powerful urge to pass our genes on to the next
generation has likely changed the face of
human culture in ways we're only beginning
to understand.
Why Sex?
Traits can be positive, negative or neutral in a
given environment.
The alleles coding for negative traits are likely
to be reduced in the presence of alleles for
more favorable ones.
Team Question
The types of variation we have been discussing
can have an impact on the success of an
organism.
Biologically speaking, what is “success?”
Essential requirements for Evolution
Variation: All life forms vary genetically within a
population. It is this genetic variation upon which
selection works.
Inheritance: Genetic traits are inherited from parents
and are passed on to offspring.
Selection: Organisms with traits that are favorable to
their survival get to live and pass on their genes to the
next generation.
Time: Evolution takes time. Evolution can happen in a
few generations, but major change, such as speciation,
often takes long periods of time.
CHARLES DARWIN – 1809-1882
• English
• Traveled around the world on
the Beagle – famous in the
Galapagos islands
• Observed many species and
fossils
• Why did some species survive
while others became extinct?
• Natural selection
Voyage of the HMS Beagle
Stopped in Galapagos Islands 500 miles off coast of Ecuador
I have called this principle,
by which
each slight variation, if
useful, is preserved,
by the term Natural
Selection.
—Charles Darwin from "The
Origin of Species"
NATURAL SELECTION
Organisms with traits
well suited to an
environment are more
likely to survive and
produce more offspring
than organisms without
these favorable traits
Types of selection
There are three types of selection: disruptive, stabilizing
and directional.
Selection causes some traits to survive and spread, while
others are lost. A selection pressure determines which traits
are successful.
Starting population has
a normal distribution
of traits.
number of
individuals
Selection can be represented using graphs showing the
distribution of individuals with a particular trait.
mode
trait
Types of selection
Selection can cause the mode and/or distribution to change.
mode
number of
individuals
mode
number of
individuals
number of
individuals
mode
trait
disruptive
Selection
pressure toward
the extremes
creates two
modal values.
trait
stabilizing
Selection pressure
toward the center
increases the
number of
individuals at the
modal value.
trait
directional
Selection
pressure toward
one extreme
moves the mode
in this direction.
LaMarck
Earlier ideas on Evolution
– evolution by acquired traits
• creatures developed traits
during their lifetime
• give those traits to their
offspring
– example
• in reaching higher
leaves giraffes stretch their
necks & give the acquired
longer neck to offspring
– not accepted as valid
Darwin’s view of Evolution
– giraffes that already
have long necks
survive better
– leave more offspring
who inherit their
long necks
• variation
• selection &
survival
• reproduction &
inheritance of
more fit traits
Could Darwin explain everything?
Darwin made extensive use of
specimens and fossil evidence to
explain his theory of evolution,
but because DNA and
genes had not yet been
discovered, he was unable
to explain why traits varied within
individuals or how they were inherited.
Victorian scientists found it difficult to test Darwin’s
theory. For his theory to work, the Earth needed to be
millions of years old, but its age was not known at that time.
In addition, little was known about the process of fossilization
or how to explain gaps in the fossil record.
Natural Selection
1.
2.
3.
4.
Overproduction
Competition
Variations
Survival of the fit
1. Overproduction
Organisms produce
more offspring than
the environment can
support.
There is not enough
food or living space
for all the offspring.
2. Competition
Overproduction leads to a struggle.
All the organisms compete for food, water, and
the other necessities of life.
Only those organisms that are well suited to their
surroundings survive and reproduce.
The rest die.
3. Variations
Organisms of the same species are very
similar.
But they do have individual differences
among traits, or variations.
These differences are important in the
”struggle for survival.”
For example, extra speed can mean the difference
between life and death. A fast wildebeest may
escape an attacking lion. A slower neighbor may
become the lion’s next meal.
4. Survival Of The Fit
Organisms with traits that
make them well adapted,
or suited to the
environment, survive and
reproduce.
Darwin used the term
natural selection to
describe the survival of
organisms with favorable
traits.
They, in turn, pass their favorable traits to
their offspring.
The offspring are then more likely to
survive.
As the process of natural selection goes on
over many generations, species change.
Galápagos finches
In the Galápagos, Darwin noticed that different islands had
different types of finches, with different types of beak.
 Some finches had strong and claw-like
beaks, suitable for crushing seeds.
 Other finches had thin and delicate beaks,
suitable for picking insects from holes in
the ground.
Darwin thought all the finches could have evolved from one
type of finch that came from the mainland.
Natural variation meant that some finches had slightly
different beaks. These finches would have been able to eat
different types of food and avoid competition. They would
therefore have survived and passed on their genes.
Darwin’s finches
Darwin’s conclusions
– variations in beaks
• differences in beaks in the original flock
• adaptations to foods available on islands
– natural selection for most fit
• over many generations, the finches were selected for
specific beaks & behaviors
– offspring inherit successful traits
• accumulation of winning traits:
both beaks & behaviors
– separate into different species
Peppered moths
Peppered moths rest on tree trunks
during the day. Some are light
colored and others are dark.
When cities were very polluted in the
19th century the number of
previously rare dark colored moths
increased, as they were better
camouflaged against predators on
soot-stained trees.
Cities are cleaner now. What
difference has this made?
The number of light colored moths is
increasing.
These changes can result in the appearance of a
new species.
Evolution by natural selection occurs.