Transcript Evolution PREAP 2015

Evolution and Adaptation Notes
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 7
What is Evolution??
Evolution
 Evolution - Change in a kind of organism over time;
process by which modern organisms have descended
from ancient organisms.
What is a Theory versus a Hypothesis?
https://www.youtube.com/watch?v=85diEXbJBIk - video 1
Hypothesis
 An educated guess
that has to be testable
by scientific methods
Theory
 Has to be wellsupported and has
been tested over and
over
 Is an explanation of a
phenomena that has
occurred in the
natural world.
Origins of Evolutionary Thought
1. 1785 - James Hutton: Proposes
that earth is shaped by geological
forces that took place over extremely
long periods of time (gradualism).
He estimates Earth to be millions –
not thousands – of years old.
2. 1798 – Thomas Malthus: Predicts
that the human population will grow
faster than the space and food
supplies needed to sustain it.
Origins of Evolutionary Thought
3. 1809 – Jean-Baptiste Lamarck:
Proposed that changes in environment
caused an organism to have greater use
or disuse of a structure/organ. His ideas
are flawed, but he is one of the first to
propose a new mechanism explaining
how organisms change over time
(inheritance of acquired traits).
4. 1833 – Charles Lyell: Observed
processes that made small changes in
Earth’s features are uniform through
time and have shaped Earth’s geological
features over long periods of time.
Charles Darwin
 During Darwin’s trip around the world he noticed all the
variation (different physical traits of an individual in the
group it belongs) of traits among similar species.
Charles Darwin - The Galápagos Islands
 Giant tortoises & Finches varied according to the island each
inhabited. These species were able to adapt with adaptations (
a feature that allows an organism to better survive and
reproduce in its environment) to their surroundings.
Charles Darwin- insight leading to natural selection
 Darwin noticed lots of variation of species in nature
and on farms.
 Saw breeders were selecting only the largest hogs, the fastest horses,
or the cows that produced the most milk and breeding those with
each other. Darwin termed this process artificial selection.
 Artificial selection –When humans select those variations
provided by nature that they found useful/beneficial.
Charles Darwin- insight leading to natural selection
 Darwin used all prior scientist knowledge along
with his own findings and proposed a mechanism
for evolution called natural selection.
Darwin’s Conclusions
Evolution Occurs by Natural Selection
1. Struggle for survival exists in nature
Competition among members of a species exist for
food, living space, and the other necessities of life.

Survival of the Fittest – Individuals that are better suited
to their environment – that it, with adaptations that
enable fitness – survive and reproduce more successfully;
Darwin referred to this as natural selection

1.
Fitness - Ability of an organism to survive and reproduce relative to
other members of the population in its environment.
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 4
Darwin’s Conclusions
Evolution Occurs by Natural Selection
2. Adaptation
 Certain variations allow individuals to adapt and
survive better in their environment. Those more
successful will live longer and share those
adaptations to future generations.
 Natural selection cannot be seen directly; it can
only be observed as changes in a population over
many successive generations.
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 6
Adaptations
 Adaptation – Inherited characteristic that
increases an organism’s chance of survival.
 Can be either physical or behavioral.
 Animals have evolved their adaptations.
 A long period of slow change resulted in an animal’s adaptations.
 Example: The spots on the snow leopard did not emerge overnight. Instead, this
process took generation upon generation of snow leopards physically adapting to
their environment for characteristic spot patterns to evolve. Those leopards with
spot patterns were able to hide more successfully, therefore surviving longer than
those without spots. This allowed the longer surviving snow leopards to
reproduce and create more snow leopards with spot patterns like their own.
 This process of change over time is the key to how many organisms develop
adaptations.
 Some adaptations can arise quickly through genetic mutations as well.
But some mutations can be deadly as well.
Darwin’s Conclusions
Evolution Occurs by Natural Selection
3. Decent with Modification
Darwin proposed that over long periods, natural selection
produces organisms have different structures, establish
different niches, or occupy different habitats = species
today look different from their ancestors.
 Each living species has descended, with
changes, from other species over time.
 Darwin referred to this principle as
descent with modification
Darwin’s Conclusions
Evolution Occurs by Natural Selection
4. Variation
Many genes have at least two genes or alleles.
 Animals such as dogs, horses, and mice often have several alleles
for traits such as body size or coat color.
 All organisms have additional genetic variation that is “invisible”
because it involves small differences in biochemical processes.
 An organism can be heterozygous for many genes.
Evidence of Evolution
comes primarily from these sources….
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video
3
1. Fossil record
2. Geographical distribution of living species
3. Structural similarities of related life forms
4. Chemical similarities in DNA
5. Embryology
Evidence of Evolution: Fossil Record
 Fossils are direct or indirect
remnants of the past.
 The fossil record provides evidence
about the history of life on Earth. It
also shows how different groups of
organisms, including species, have
changed over time, that life on
Earth has changed.
 The fossil record is not completethere are gaps but they are being
filled as we speak!!!
 99% of living species are now
extinct
Fossil record of horses
In 1974 remains of this skeleton
were found in Ethiopia and lived
3-3.9 million yrs ago. She was 3
ft. 8 in tall and weighed ~65 lbs.
Because of her pelvis she was one
of the first to show upright
walking. She has a really small
skull but front teeth like a human.
“Lucy’s baby” – in 2006 they
found the oldest earliest child
fossil in Ethiopia – about 3 yrs
old, female, skull, milk teeth, tiny
fingers, torso, foot and kneecap
(no bigger than a dried pea) –
more complete than Lucy and
120,000thousands of years older
even.
Age of Fossils
 Paleontologists determine
the age of fossils using two
techniques:
1. Relative
dating
2. Radioactive
dating
Relative Dating
Radioactive Dating
Relative Dating

In relative dating, the age
of a fossil is determined by
comparing its placement with
that of fossils in other layers of rock.

Paleontologists estimate the age based on the age of other fossils found
near it.

It’s not absolute and doesn’t tell the age in years..
 The rock layers form in order by age:
• The oldest layers on the bottom
• More recent layers on top (closer to Earth's surface)
Radioactive Dating
 Scientists use radioactive decay
to assign absolute ages to rocks.
 Some elements (C, K, Ar) found
in rocks are radioactive.
 Radioactive elements decay, or break down, into
nonradioactive elements at a steady rate, which is measured
in a unit called a half-life.
 In radioactive dating, scientists calculate the age of a
sample based on the amount of remaining radioactive
isotopes it contains.
Radioactive Decay
 A half-life is the length of
time required for half of
the radioactive atoms in a
sample to decay.
 After 1 half-life - Half of
the original radioactive
atoms in a sample have
decayed.
 Of those remaining atoms,
half again are decayed after
another half-life.
Evidence of Evolution: Biogeography
 Similar, but unrelated species exist.
Similar animals in different
locations were the product of
different lines of evolutionary
descent.
 Some animals on each continent live
under similar ecological conditions.


Are exposed to similar pressures of natural
selection.
Because of these similar selection
pressures, different animals ended up
evolving certain striking features in
common.
Evidence of Evolution:
Structural Similarities
of Living Things
1. Homologous
Structures
2. Analogous Structures
3. Vestigial Structures
Homologous Structures of Living
Organisms
 Researchers had noticed
striking anatomical similarities
among the body parts of
animals with backbones.
 Example: The arms of reptiles,
wings of birds, and legs of
mammals vary greatly in form
and function.Yet, they are all
constructed from the same
basic bones.
Homologous Structures
 Homologous Structures - Structures that have different
mature forms in different organisms but develop from the
same embryonic tissues.
 Same development - different function.
 Provide strong evidence that all four-limbed vertebrates have
descended, with modifications, from common ancestors.
Analogous Structures
 Analogous Structures - Structures that evolve separately to
perform a similar function.
 Different development – same function.
 Provides evidence for convergent evolution because they
have very similar structures even though they were completely
independently derived to fill a similar purpose.
 Examples: Wings of birds,
bats, and insects (have
different embryological
origins but are all designed
for flight).
Vestigial Organs
 Vestigial Organs – Organ that
serves no useful function in an
organism; Traces of homologous
structures.
Examples:
Hip bones found in whales,
salamanders, and pythons
2. Eye bulbs of blind, cave-dwelling
creatures, such as the grotto
salamander.
3. Human coccyx bone (tail bone) –
lost original function of a tail but
now serves as places for bones to
attach
1.
Evidence of Evolution: Chemical Similarities
 All of the tens of thousands of types of proteins in
living things are made of only 20 kinds of amino acids.
 Despite the great diversity of life on our planet, the simple
language of the DNA code is the same for all living things.
 This is evidence of the fundamental molecular unity of life.
 New technologies, such as
DNA fingerprinting, have
helped to fill in gaps in the
fossil record.
Amino Acid Comparison
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html - video 5
 The more closely related two
species are, the more amino acid
sequence similarities should be
seen.
A
B
C
D
E
F
 Try to guess which embryo is the:
 Chicken?
 Rabbit?
 Fish?
 Human?
G
H
Evidence of Evolution: Similarities in
Embryology
 The early stages, or embryos,
of many animals with
backbones are very similar.
 Many embryos look
especially similar during early
stages of development.
 The same groups of
embryonic cells develop in
the same order and in similar
patterns to produce the
tissues and organs of all
vertebrates.
EVOLUTION OF POPULATIONS
How does a population of penguins evolve??
Variation increases chance of survival
 Genetic variation is studied in
populations.
 A population is a group of
individuals of the same species
that interbreed.
 Because members of a population
interbreed, they share a common
group of genes called a gene pool.
 Gene Pool - Consists of all genes,
including all the different alleles, that
are present in a population.
Sources of Genetic Variation
 The two main sources of genetic variation are:
1. Mutations – Any change in a sequence of DNA.
Can occur because of mistakes in the replication of DNA or as
a result of radiation or chemicals in the environment.

2. Recombination - The natural formation in offspring of
genetic combinations not present in parents.


Independent assortment occurs during the production of
gametes – each homologous pair moves independently
during meiosis.
Crossing over during meiosis further increases variation.
Natural Selection acts on distribution of traits
 Natural selection can
affect the distributions
of phenotypes in any of
three ways:
1. Directional Selection
2. Stabilizing Selection
3. Disruptive Selection
Directional Selection
 Directional Selection – Takes place when
individuals at one end of the curve have higher
fitness than individuals in the middle or at the other
end.
 The range of phenotypes shift as some individuals fail to
survive and reproduce while others succeed.
 Ex – drug resistant bacteria
Stabilizing Selection
 Stabilizing Selection – Takes place when individuals
near the center of the curve have higher fitness than
individuals at either end of the curve.
 This situation keeps the center of the
curve at its current position, but it
narrows the overall graph.
 Example: The weight of human
infants – smaller than average babies
are likely to be less healthy and larger
than average babies are likely to have
difficulty being born.
Disruptive Selection
 Disruptive Selection – Takes place
when individuals at the upper and lower
ends of the curve have higher fitness
than individuals near the middle.
 In such situations, selection acts most
strongly against individuals of an
intermediate type.
 If the pressure of natural selection is strong
enough and lasts long enough, this situation
can cause the single curve to split into two
(can create two distinct phenotypes).
Other Mechanism for Evolution besides
natural selection
 Gene Flow - The movement of alleles (genes) from
one population to another.
 Affected by:
1. Mobility
2. Barriers
3. Environment (wind)
Other Mechanism for Evolution besides
natural selection
Genetic Drift - Random change in allele frequencies that
occurs in small populations due to chance.
 Unlike natural selection because:
1.
2.
It happens by chance – caused by big event like overhunting or a
natural disaster (fire, landslide or lightning strike).
Doesn’t work to produce adaptations like natural selection
does.
How Does Genetic Drift Occur?
1. In each generation, some individuals may, just by
chance, leave behind a few more descendants (and
genes, of course) than other individuals.
2. The genes of the next generation will be the genes of
the “lucky” individuals, not necessarily the healthier
or “better” individuals.
3. It happens to all
populations – there’s no
avoiding the vagaries of
chance.
Evolution vs. Genetic Equilibrium
 To clarify how evolutionary change operates,
scientists often find it helpful to determine what
happens when no change takes place.
 So biologists ask: Are there any conditions under
which evolution will not occur?
The Hardy-Weinberg Principle
Hardy Weinberg Equation: p2 + 2pq + q2 = 1
p+q=1
Hardy-Weinberg Principle
 Five conditions are required to maintain genetic equilibrium
from generation to generation:
1.
There must be random mating.
o
2.
The population must be very large.
o
3.
Individuals may bring new alleles into a population.
There can be no mutations.
o
5.
Genetic drift has less effect on large populations than on small ones.
There can be no movement into or out of the population.
o
4.
All members of the population must have an equal opportunity to
produce offspring, which ensures that each individual has an equal
chance of passing on its alleles to offspring.
If genes mutate from one form into another, new alleles may be
introduced into the population, and allele frequencies will change.
There can be no natural selection.
o
No phenotype can have a selective advantage over another.
The Hardy-Weinberg Equation
p2 = Frequency of AA
2pq = Frequency of Aa
q2 = Frequency of aa
p = Frequency of A
q = Frequency of a
For example: If the frequency of two alleles in a gene pool is 90% A , and
10% a, what is the frequency of individuals in the population with the
genotype Aa?
Solve: p = frequency of A, which is .9 (90%)
q = frequency of a, which is .1 (10%)
2pq = frequency of Aa = 2(.9)(.1) = .18
Therefore, the frequency of individuals with genotype Aa would be .18
The Process of Speciation
 How do these changes from
natural selection or chance lead to
the formation of new species, or
speciation?
 Species - Group of organisms that
breed with one another and produce
fertile offspring
Speciation & Reproductive Isolation
 The gene pools of two populations must become
separated for them to become new species.
 As new species evolve, populations become
reproductively isolated from each other.
 Reproductive Isolation - When the members of two
populations cannot
interbreed and
produce fertile
offspring.
Reproductive Isolation
Reproductive isolation
occurs when members of
different populations can
no longer mate
successfully.
1. Behavioral Isolation
2. Geographic Isolation
3. Temporal Isolation
Behavioral Isolation
 Behavioral Isolation - Two populations are capable of
interbreeding but have differences in courtship rituals
or other reproductive strategies that involve behavior.
 Example: Eastern and Western Meadowlarks
 Members of the two species will
not mate with each other partly
because they use different songs
to attract mates.
 Eastern meadowlarks will not
respond to western
meadowlark songs, and vice
versa.
Geographic Isolation
 With geographic isolation, two populations are
separated by geographic barriers such as rivers,
mountains, or bodies of water.
 Example: The Abert & Kaibab Squirrel
 About 10,000 years ago, the Colorado River split the species into
two separate populations.
 Two separate gene pools formed.
 Natural selection worked
separately on each group
and led to the formation
of a distinct subspecies, the
Kaibab squirrel.
Temporal Isolation
 Temporal Isolation - Form of
reproductive isolation in which two
populations reproduce at different
times.
 Example:
 Three similar species of orchid all
live in the same rain forest.
 Each species releases pollen only
on a single day.
 Because the three species release
pollen on different days, they
cannot pollinate one another.
Patterns of Evolution
 Some large-scale evolutionary patterns and processes that
occur over long periods of time are:
1.
2.
3.
4.
5.
6.
Extinction
Convergent Evolution
Divergent Evolution
Gradualism
Punctuated Equilibrium
Coevolution
Extinction
 More than 99% of all species
that have ever lived are extinct.
 Extinctions happen because
species compete for resources,
and environments change. Some species adapt and change. Others
gradually become extinct in ways that are often caused by natural
selection.
 Each disappearance of species left habitats open and provided
ecological opportunities for those organisms that survived. The
result is often the burst of evolution that produces many new
species.
 The extinction of the dinosaurs cleared the way for the evolution of
modern mammals and birds.
Convergent Evolution
 Convergent Evolution – Process by which
unrelated organisms come to resemble one
another. (analogous structures)
 Examples:
1. Natural selection may mold different body structures, such as arms and legs,
into modified forms, such as wings or flippers. The wings or flippers function
in the same way and look very similar.
2. The similar nature of the wings of insects, birds, pterosaurs, and bats. All four
serve the same function and are similar in
structure, but each evolved independently
and not from a common winged ancestor.
Divergent Evolution
 Divergent Evolution – The process of two or
more related species becoming more and
more dissimilar. (homolougous structures)
 A single species or a small group of species have
evolved, through natural selection and other
processes, into diverse forms that live in different
ways.
 The vertebrate limb is one example of divergent
evolution. The limb in many different species has a
common origin, but has diverged somewhat in
overall structure and function
Gradualism vs. Punctuated Equilibrium
 How quickly does evolution
occur?
 Gradualism – Long time
with gradual change.
 Punctuated Equilibrium Long, stable periods
interrupted by brief periods
of more rapid change.
 Think about this…How
did a tiger get its
stripes? Gradually or
with a huge, quick
change?
Coevolution
Coevolution – the process in which two or more species evolve
in response to changes in each other.
Common Misconceptions
 Humans did not come from monkeys. Instead, humans
and primates share a common ancestor.
 Darwin is not the only evolutionary theorist. Darwin
utilized evidence from other evolutionists to draw his
conclusions.
 Evolution does not happen
quickly – it occurs over
generations of time.
 Change does not occur at the
individual level – it occurs in
populations.
Cladogram
 Cladogram – Diagram that shows the evolutionary
relationships among a group of organisms.
 Is constructed using derived characters, which are
characteristics that appear in recent parts of a lineage but not
in older members.
Phylogeny
 Phylogeny - Study of evolutionary relationships
among organisms.
 Biologists now group
organisms into categories
that represent lines of
evolutionary descent, or
phylogeny, not just physical
similarities.
Now watch the Homer Simpson video
again…..
 http://www.youtube.com/watch?v=faRlFsYmkeY
 Why is this cartoon inaccurate? Use the information
that you’ve learned about evolution in this unit!
Adaptions
 Catepillar that looks like a snake