Download Evolution 3/2/14

Evolution 3/2/14
So what is Evolution anyway?

Definition: A change over time

More specifically: change in relative
frequency of alleles in a population

Note the word “POPULATION”

INDIVIDUALS DO NOT EVOLVE
Sources of Change
1.
Sexual Reproduction ( Random Shuffling of
alleles)
2. Mutations
3. Geographic isolation
So, What does Darwin have to do with it?
Charles Darwin

Born in England February 12, 1809 to a
wealthy family

attended Oxford University

became a naturalist

joined the crew of the H.M.S. Beagle for
a 5 year voyage (1831)
What Darwin learned from
the voyage

made numerous observations and collected data
that led him to propose a revolutionary hypothesis
about the way life changes (evolution).
Darwin’s
Observations:1. Patterns of
Diversity
plants
and animals are
well suited to whatever
environment they inhabit
2. Living Organisms and Fossils
collected remains of
preserved organisms called fossils.
Some of the fossils resembled
organisms that were still alive and
others looked completely unlike
any creature he had ever seen.
3. The Galapagos Islands
characteristics of many animals and
plants varied noticeably among the
different Galapagos Islands.
 Ex. The tortoises shape of the shell
corresponded to different
habitats. Hood Island tortoise – long
neck and curved shell that is open
and allows it reach sparse vegetation
Hood Island

Isabela Island(below)
Pinta
Island
Other Organisms

noticed that the finches on the Islands all
had different beaks

likely that a few finches founded the
population but mutations over time
allowed them to eat different foods.

New beaks continued to be passed to the
next generation which eventually led to
different species
Variety of Finches

Plants also undergo the same
pressures of the environment

Variety of vegetation found based
on the type of climate that exists
Evolution by Natural
Selection
Definition: process by
which individuals that
are better suited to
their environment
survive and reproduce
most successfully.
Artificial Selection

using genetic variation to improve crops
or livestock ; artificial selection

Artificial selection: nature provided the
variation and humans select those
variations that they found useful.

EX: dogs, horses, corn, tomatoes, pig, cow, etc.
Not a random process!

— The
mutation is random, but
selection acts on that variation in
a very non-random way: genetic
variants that aid survival and
reproduction are much more
likely to become common than
variants that don't. (University of
Berkeley)
5 major points to natural selection

1. Genetic variations exist in populations.
Some variations are more favorable than others.
These variations are inherited.

2. Organisms produce more offspring than
can survive.

Those that do not survive, do not reproduce.



3. Overproduction of offspring forces
competition for resources. Darwin called
this the struggle for existence.
Not all offspring can possibly survive.
4. Individuals with favorable variations
have more “fitness” ;more likely to
survive and pass those variations on to
their offspring.

5. Species alive today are
descended with modification from
ancestral species that lived in the
distant past.

Darwin called this descent with
modification.
Survival of the Fittest

Link to Natural Selection example cartoon

Adaptations: any inherited trait that increases the
chances of survival and reproduction of an
organism.

Examples are:

Camouflage and Mimicry – allow animals with
successful variations survive and reproduce

EXAMPLES IN NATURE:
Mimicry:Monarch and Viceroy, Moth and Bumblebee
Camouflage: Squirrels, Leopards, walking sticks,
Praying Mantis

There are many more adaptations
besides camouflage and mimicry.
(Behaviors, sounds, etc.)
Evidence of evolution

1 Fossils and the fossil record

2 Geographic distribution

3 Homology

4. Vestigial Structures

5 Embryology

6 Biochemistry (the chemistry of living
organisms)
Sue, the largest, most complete
T. rex fossil ever found.
It resides at the Field Museum in Chicago.
A 12,000 year
old mammoth
1. Fossils

Remnants of organisms left behind

Ex: Scientists can compare the bones of
horses from 4 million years ago to ones from
the present day.

Fossils found in every layer of rock do not
look the same as those from modern life.

The oldest fossils are more different from
the modern day organisms than the
shallowest fossils
2) Geographic distribution




similar animals in very far away places.(
Rheas, Emus, and Ostriches)
Animals use different adaptations to
survive in similar environments even
though the environments are separated.
Analogous Structures: Different in
Structure but the same in function
These do not show evidence of
evolutionary relationships but, they do
show natural selection.
3. Homology



Many organisms have similar bones and
are closely related. These are called
Homologous structures.
Suggest a common ancestor and shows
strong evolutionary relationships
Example: Birds, turtles, alligators,
rats, humans, and whales all have
same arm bones

Put picture of human, horse, cat, bat, bird, whale here
4. Vestigial structures
any structure that is so reduced in function or
size that they are just vestiges or traces of
the original structure.
The structure may have been used in an
ancestor.
 The structure may be used in another
animal alive today.
 Examples: Appendix, small leg bones in
pythons, pelvic bones in whales
 Tonsils actually DO HAVE A FUNCTION even
though they can be removed.
Whale ancestors with legs

Whales are mammals that have no hind legs.

They are thought to have evolved from 4-legged
land animals that lived over 50 million years ago.

Paleontologists expected to find whale ancestors
that showed reduced and vestigial legs by looking
in sediments that were between 50 and 30 million
years old. Some examples of this transition are
shown below.
Ambulocetus
Pakicetus
Basilosaurus
49 million years ago
42 million years ago
40 million years ago
Picture of vestigial structures
The fish Astyanax comes in
two varieties – the surfacedwelling varitey is on the left,
the eyeless cave fish is on the
right.
5. Embryology
Of animals with backbones, the embryonic stages
look strikingly similar ; similar genes at work
What does this suggest?

Suggests a common ancestor and
evolutionary relationships

Groups of embryonic cells develop in the
same order and in similar patterns; same
genes (* Hox genes) turn on and off
during periods of development. (From
fruit flies to humans)
6. Biochemistry

The more closely related organisms are,
the more they will share in common
biochemistry (the chemistry of what
makes up their bodies)

similar DNA sequences and proteins

Relatively new means of identifying
evolutionary relationships

has led to the re-organization of the
history of several species * can tell when
species diverged from one another
Chapter 17 notes: Evolution and
Populations
Ch. 17 Is all evolution the
same?
•
No, it does not happen in the same way
across all populations.

Genetic variation in organisms is studied
at the level of a population not the
individual.

A population is a group of individuals of
the same species that live in the same
area.
populations

Members of a population of species
interbreed, therefore they share a
common group of genes called a gene
pool.

Gene Pool: all of the genes that are
present in a population. This includes all
the different alleles.

The relative (allelic) frequency of an allele
is the number of times that the allele occurs
in a gene pool compared to the number of
times other alleles for the same gene occur.
Q: How do new alleles arise?

Through random mutations.

Gene shuffling – during meiosis

Crossing over

Sexual Reproduction
Recall from Ch.16

evolution : any change in the
relative frequency of alleles in a
population.

if the frequency of the allele
changes, then the population is
evolving.
RECALL from genetics

Inheritable variation can be expressed by
either single-gene traits or by polygenic
traits.

The number of phenotypes produced for
a given trait depends on how many genes
control the trait.
Evolution can occur in three
ways

Directional selection

Stabilizing Selection

Disruptive Selection
Populations

Most phenotypes in generations form a
bell – shaped curve

The most common variety is represented
in the middle of the curve and more
extreme variations are on either end of
the curve. * (hair color)

Evolution shifts the curve by changing the
percentage of each variation.
Directional selection

Individuals on one end of the curve are
better adapted to their environment.

EXAMPLE: Beak size (finches)

The birds with the medium beak are the
majority.

Small and large beaks are on the ends of
the curve. If a drought occurs and only
the very large seeds survive, only largebeaked birds will be able to eat.
Directional selection

The average beak size increases since
more of the larger beaked finches could
survive and reproduce.
Stabilizing selection

When the average individual is best, the
population stabilizes-reduces the
percentage of organisms on the extremes

Example: Birth weight in humans stays
stable because too small a weight is
harmful for the baby and too big a weight
results in complications at birth.
Stabilizing selection
Disruptive selection

This occurs when either extreme is
better adapted for survival than the
average.

EXAMPLE: most of a species of a butterfly
are brown. But, on either end of the
population curve, you see RED and BLUE

Brightly colored butterflies resemble very
poisonous butterflies and thus, do not get
eaten.
Disruptive selection
Small populations

The percentages of alleles change more
quickly- GENETIC DRIFT – random change
in allelic frequency

Two Types of Genetic Drift:

1) If populations get separated and each
new population only has two of the four
variations, you have what is called a
FOUNDER EFFECT

Def: Change in allele frequencies as a
result of migration of a small subgroup
FOUNDER EFFECT
Bottleneck Effect *add into
notes

2) Change in allelic frequency after a
dramatic reduction in the size of a
population.

Example: a natural disaster such as a
tornado or hurricane wipes out a
population but a few individuals remain.
Those individuals may have very different
alleles from the original population.
Therefore, the population that grows will
be different from the original population.
ARE POPULATIONS ALWAYS
EVOLVING?
No, but there are 5 conditions which must
be met for a population not to be
evolving.
 Requirements to maintain genetic
equilbrium:
 1) Random mating
In nature, random mating rarely occurs.
 Example: Lions select their mates based
on size or strength.


2) Large population

3) No movement into (immigration) or out
of population (emmigration)

4) No mutations

5) No natural Selection

THIS IS KNOWN AS THE HARDY- WEINBURG
PRINCIPLE
It is difficult
for all of the
conditions to
be met.
So, how do we get a new
species? 17.3

All of these changes over time can
eventually lead to a new species

This process is called SPECIATION
3 types of speciation
 Caused
by 3 isolating
mechanisms:
 Behavioral
 Geographic

Temporal
Behavioral isolation

Occurs when two populations are capable
of interbreeding but do not. (due to
difference in rituals/ behaviors)

EX: Eastern and Western meadowlarks
both live in central US

They do not mate because they use
different songs to attract their mates
Geographic isolation

occurs when 2 populations cannot reach
each other to mate due to a physical
barrier.

EX: earthquake in CA creates a huge
crevasse in the ground, isolating a
population of lizards

Since the two populations cannot mate,
they begin to have subtle changes over
time that make them different species
Temporal isolation

Occurs when the species reproduce at
different times of the year.

EX: 3 species of orchid all live in the same
area but, they never interbreed because
they release their pollen at different
times of the year.
orchids
CH. 19 History of Life on
earth 4/13/15
And, should I
become a
paleontologist
rather than a
dentist?
Ch. 19
Geologic evidence
shows that Earth is
about 4.6 billion
years old.

By the fossil record, scientists have
learned that not all types of animals
appeared all at once.
Fact: more than 99 percent of all species
that have ever lived on Earth have
become extinct.
Earliest life forms appeared in rocks more
than 3.5 billion years old.

Paleontologists – scientists who study
fossils
Fossils… what do you look at?



1.Anatomical similarities and differences
between the fossil organism and organisms
living today.
2. The fossil’s age.
3. What the environment may have been
like when the organism was alive. This
may tell you what the organism ate and
how it lived.
Dating Methods

1) Relative: The age of the fossil is
determined by comparing its placement in
the sedimentary rock with that of fossils
in other layers

Index fossils are used
What are index fossils?
Fossils of a species that are easily
recognized.
Existed for only a short period of time
so it will only be found in a few
layers of rock.
Had a wide geographic distribution. *
meaning that it can be found in
many locations around the world.

Rocks and sediments are deposited on the
earth in layers.

By looking at the layers, we can tell what
order they were deposited in.

What does this show? change in species
through time
Radioactive dating link *2:58

To 50 seconds then fast forward to 2:58 to 3:28

2) Radioactive: calculate absolute ages




of the fossil based on the amount of
remaining radioactive isotope it
contains.
Different radioactive isotopes have
different half-lives (rates of decay).
Half Life: time it takes for half of the
radioactive atoms in a sample to decay
EX: Carbon-14: decays into nitrogen-14
every 5739 years which is called the
half-life.
EX: Potassium-40: decays into argon40 every 1.26 billion years.
How does Radioactive dating
work exactly? (carbon dating)

All plants and animals incorporate carbon into their
tissues during their lives for growth and energy.
(eating)

When an organism dies, it stops incorporating
carbon (all forms of carbon, including C14) into its
structure.

The amount of radioactive carbon (C14) that had
been in the organism when it was alive begins to
decrease at death as it loses nuclear particles
through radioactive decay.

C14 is only good for dating fossils younger than 60,
000 years old

the "clock" starts ticking when death occurs.
Sequence of events (per the
geologic record)

Early bacteria-like cells/ prokaryotes

First Eukaryotes

Fish and simple plants

Amphibians

Reptiles and bush-like plants

Birds and trees

Simple mammals (rodents)

Primates
What was the Earth like before
PreCambrian time? Link
*after 4:07
Earth’s atmosphere did not contain oxygen,
so microorganisms were the first to
appear (prokaryotic) ….in the water
Once oxygen appears, eukaryotic organisms
appear.
Theory of Endosymbiosis –
Eukaryotic cells arose from living
communities formed by prokaryotic cells.
Theory of endosymbiosis

Mitochondria and chloroplasts contain
their own DNA

Mitochondria and chloroplasts have
ribosomes that make their own proteins.

Like bacteria, mitochondria and
chloroplasts have many of the features of
free-living bacteria such as being able to
grow and reproduce independently of the
cell.
A Brief History of Time

Since all organisms have appeared
sequentially, it would seem logical to
assume that each gave rise to the
other…..
 This
is not the case.
Evolution states that organisms share
ancestors not that one evolved into
another.
Rates of Evolution

Evidence shows that evolution has
proceeded at different rates for different
organisms at different times.

1.) Gradualism- Gradual change/ slow
and steady change

2.) Punctuated Equilibrium- equilibrium
interrupted by brief periods of rapid
change.

Rapid can mean a few thousand years in
terms of geologic time.
The Peppered
Moth
link

Rapid evolution occurs most frequently in
small populations.
EX: - founder effect, bottleneck effect
Patterns of evolution in
populations

Adaptive radiation

Convergent evolution

Coevolution

extinction
Adaptive radiation/ divergent
evolution
A
single species evolves into
more populations by creating
adaptations to different
environments or niches
 EX:
Galapagos finches –
 Hawaiian
Fruit flies -
Convergent evolution

Unrelated organisms resemble each other
since they have adapted to the same
environment.

Ex: fish and dolphins both have fins

Ostriches, Rheas, and Emus,

Flying Squirrels and Sugar Gliders

Birds and dragonflies both have wings

RECALL: These are called analogous
structures ( same function but different
structure)
Coevolution

When two species evolve in response to
one another

EX: Flowers and their pollinators must
evolve together. If the flower has a
mutation that no longer attracts the
hummingbird, it will not reproduce….and
then, the hummingbird will have to find a
new food source.
Extinction

When a species cannot adapt to its
changing environment

Competition

Climate change

So much to learn, so little time!

Evolution is a whole course in college all
by itself!