Download Evolution Keystone Presentation Part 1

Evolution and
Natural Selection
Review Presentation
for Biology Keystone
Assessment
Created by Joshua Collins
2011
Table of Contents
1) What is Evolution?
2) Natural Selection
3) Evidence for Evolution
4) Evolution in Action
1) What is
Evolution?
2) Natural
Selection
3) Evidence for
Evolution
Section 1 of 4:
What is
Evolution?
4) Evolution
in Action
1) What is Evolution?
Evolution  the process by which species
gradually change over many generations
through natural selection.
Important things to consider:
• No individual organism can evolve, but given the right
conditions over enough time, traits within a population will
gradually change until the entire population is different.
• Populations tend to evolve due to external environmental
factors such as predators, food sources, and changes in climate.
• New species arise through this very process, and all life on
earth can be traced back to simpler common ancestors.
• Species  A group of organisms that evolved together
and are genetically similar enough that they
can mate and produce fertile offspring.
• Adaptation  A specific physical trait or instinctual
behavior that has evolved within a species
to help it survive in its environment.
• Micro-evolution  Evolution within a species over
several generations.
• Macro-evolution  Long term evolution over thousands
of generations or more, leading to
the origination of new species
(called speciation).
Keep in mind, there really is no difference between
micro and macro-evolution, except the amount of time.
Common ancestor of
species A1 and A2.
Species A1
Species A
Species A2
Two distinct
species, no
longer capable
of interbreeding.
If one population becomes separated into two isolated groups,
given enough time, the two groups will become different species.
• Outer twigs represent species.
• Kingdoms and phyla represented by
the thicker branches of the tree.
• Splitting branches show new species
branching off from a shared ancestor.
• Closely related species branched off
from each other more recently.
• Distantly related species branched
off much closer to the bottom.
• All the species share a common
ancestor at the trunk of the tree.
Common
ancestor
(shared by all the descendants)
A dead end branch
represents an extinction.
Where is the most recent
common ancestor between
squirrels and whales?
All these species trace their lineage
back to this common ancestor,
essentially the first mammal.
Less
related
to a cow
More
related
to a cow
cow
Sharks and
cows have a
very ancient
common
ancestor
Pigs and cows
have a relatively
recent common
ancestor.
All vertebrates trace back
to this common ancestor.
1) What is
Evolution?
2) Natural
Selection
3) Evidence for
Evolution
Section 2 of 4:
Natural
Selection
4) Evolution
in Action
2) Natural Selection
Charles
Darwin
Natural Selection 
•
The driving mechanism
behind evolution, as
explained in Darwin’s
Origin of Species
•
Certain organisms survive
to pass on their traits to
successive generations,
but most do not.
•
Often summed up as
“survival of the fittest”
Darwin’s work was heavily influenced by the previous
ideas of other naturalists, including Malthus’ research
on population.
No population can grow indefinitely.
Many more offspring are born than
will actually survive to pass on their
genes. Therefore, individuals must
compete for resources to survive.
For example:
If every baby robin survived to
adulthood and reproduced, it
would only take a few decades
before the entire planet would
be overrun by robins!
Obviously, this does not happen!
Darwin recognized that limited resources in any environment lead
to a “struggle for existence”, in which the traits of some individuals
will give them an advantage over others. However slight this
advantage, it will lead to certain traits being “selected” by nature
to survive and reproduce… Hence, natural selection!
These pigeons have all been bred by humans
to have certain exaggerated characteristics.
Darwin also realized that natural selection is basically
the same process that humans have used for centuries
in selective breeding of domesticated animals as well as
plants for agriculture.
Selective breeding, or “artificial
selection” is the same process that
has led to all the variation we see
in dog breeds today.
• In artificial selection,
humans speed up the
change in traits by
doing the selecting
themselves.
• In natural selection,
nature itself is doing
the selecting over
thousands of
generations.
1) Natural Selection
Darwin knew this
• The mechanism (driving force) for evolution,
as explained by Charles Darwin.
• Explains changes in an entire species or
population (not individuals) over time.
Darwin didn’t
2) Mutations
• Random changes in DNA are sometimes
passed on to offspring.
• Some helpful; some harmful; some neutral
• Only traits that increase reproductive
fitness will continue to be passed on.
know this
because he
didn’t know
about…
A
T
Deoxyribonucleic Acid
G
C
•
Ironically, Darwin never
found out about the work
of Gregor Mendel, who
was experimenting with
pea plants right around
the same time, in order to
figure out how traits are
inherited.
•
It was decades later that Mendel was finally
recognized as the father of genetics.
•
For Darwin, this was the one missing piece
of the puzzle that would have vindicated his
entire theory.
•
It wouldn’t be until 1953 that the genetic
code itself was finally cracked by Watson
and Crick in their discovery of the doublehelix structure of DNA.
• Gene  A section of DNA that codes for a particular
protein, physical trait, or function
• Allele  One of two (or more) different forms of a gene; For
example, for the eye color gene, one allele codes
for blue eyes, while the other codes for brown.
Often, one allele is dominant over the other.
• Genotype  The combination of alleles for a particular
gene; one allele comes from the mother and
the other from the father.
• Phenotype  The trait that results from the genotype
Genes are made up of
complex combinations
of the base pairs.
A T
GC
• Some genes code for proteins and enzymes.
• Some genes turn other genes on or off.
• Large sections of DNA code for NOTHING!
• If stretched out, the DNA from
the nucleus of each cell in your
body would be over 6 feet long!
• Billions of DNA bases have to
be copied every time your
body makes new cells, which
happens continuously.
• There are over 50 trillion
cells in your body!
• A mutation is simply when
there is an error in this
copying process.
• This happens all the time!
• When the right kind of
mutation happens in the
right kind of way, the
mutated gene becomes
part of the gene pool and
natural selection
continues.
Keep in mind:
Mutations themselves are
random “mistakes”, but
natural selection is not
random! The tiniest
genetic change will be
favored if it increases an
organism’s chances for
survival or reproduction,
even the slightest bit.
These tiny changes accumulate
over the course of millions of
years until the descendants have
gradually diverged from their
ancestors into a new species (or
multiple different species).
Natural selection occurs
through the following steps:
1)
2)
3)
4)
Overproduction
Inherited variation
Competition
Reproduction
1) Overproduction
Parents produce more offspring
than will survive. Similarly, plants
produce thousands of seeds even
though only a few may germinate.
3) Competition
In any population, organisms must
compete for resources to survive.
Some individuals have traits which
allow them to survive better than
others; often referred to as
“survival of the fittest”.
2) Inherited Variation
There are genetic differences in
any population which result in
many combinations of different
traits among offspring. These
traits are passed genetically from
parents to offspring.
4) Reproduction
Those who have a survival advantage
are more likely to reproduce and pass
on their favorable genes and traits to
successive generations, resulting in
new adaptations and eventually new
species.
The peppered moth study is a
perfect case study of natural
selection in action.
•
In the early 1800s, a common moth
species in England had light-colored
peppered wings, which helped it blend in
with the light bark on the trees in the area.
•
This camouflage trait helped the moth
avoid being eaten by birds.
•
In 1848, a new dark form of the moth
began appearing, and by the turn of the
century, the dark variety made up the vast
majority of the moth population.
Why did the light moths die off, while the dark ones flourished?
• Something must have
changed that gave the
dark moths a survival
advantage.
• Scientists recognized that
moths were changing in
response to a change in
their environment.
• Extensive air pollution
from industrialization was
causing the tree bark to
darken with coal soot.
1) Overproduction
Peppered moths lay many eggs, and
out of those that hatch, the vast
majority of them will be eaten and
will not survive to lay eggs of their
own.
3) Competition
Since there are so many moths, some
will survive, but most will die. The
ones that survive tend to be the ones
that have traits favorable for survival,
in this case, camouflage.
2) Inherited Variation
Traits for light or dark color are passed
on genetically, and moth offspring tend
to have traits similar to their parents.
However, within a population, some
are lighter and some are darker.
4) Reproduction
The moths that best blend in with
their surroundings will be more likely
to survive to adulthood and lay eggs,
which will yield offspring with those
same favorable camouflage traits.
Can you
spot the moth?
Keep in mind:
• No individual moth ever changed its color. Some moths simply survived
better than others, changing the allele frequency, therefore changing
the appearance of the color traits among the entire population.
• In other words, the light moths didn’t become darker. They just tended
to die out, allowing the dark moths to take over!
Can you
spot the moth?
Keep in mind:
• No individual moth ever changed its color. Some moths simply survived
better than others, changing the allele frequency, therefore changing
the appearance of the color traits among the entire population.
• In other words, the light moths didn’t become darker. They just tended
to die out, allowing the dark moths to take over!
Long after the Industrial
Revolution, pollution regulations
have helped to clean the soot
from England’s trees.
And guess what
happened to the
dark moths…
Dark-colored moths started to be eaten
more and more as the tree bark
lightened, eventually allowing the light
moths to repopulate once again.