Evolution Class Notes
Transcript Evolution Class Notes
Unit Learning Goals
a. Trace the history of the theory.
b. Explain the history of life in terms of
biodiversity, ancestry, and the rates of
Age of Earth
Where do I live?
• What type of
environment am I
best “fit” for?
• Organisms have
traits (GENES) that
help them to
survive in different
A variation is a small change in a trait that makes
an individual slightly different from other members
of its species.
• All organisms in a
population are not
• What causes this
What is Fitness?
• Fitness is a measure of
(survive long enough to
• Reproductive success:
Having traits so that an
organism is able to pass on
genes onto the next
generation (and in a way so
that the next generation can
also pass those genes on)
• Any trait that promotes
survival — at least until one's
reproductive years are over
• Such traits are called
What if an organism has a trait. 6
that makes it impossible to live in
• The organism will
• If it does not
• If it does not
genes are not
passed to the next
What if the environment changes? 7
• If they do not have the traits (genes)
that enable them to survive…they die,
and DO NOT reproduce.
• If they do have the traits, then they
– SO… the next generation has more of the
“fit” traits for THAT environment.
• The population then CHANGES!
– This is a very slow process….does not occur
over night…many generations must past before
any change in the population can be seen.
Current Theory …
•Also know as “survival of the fittest.”
•Only certain members of the
population will survive and reproduce.
•Ones that survive are most suited to
the environment—they are the most
survival of the fittest
Humans have been doing this for 1000s of years!
Humans select and breed for certain traits.
Examples: The largest hog, the cow that gives
the most milk, fastest horse, or cutest dog.
Where do NEW
How do new traits arise?
b) Sexual Reproduction.
– Mixing of genes makes new
– A combo of traits may be necessary
for survival……so… sexual
reproduction and crossing over can
create new combination of traits.
Decent with modifications
These changes increase
a species’ fitness in their
THE BASICS: A review
• ADAPTATIONS (traits) that are
favorable become more prevalent
within that population.
• These traits will be passed on to the
• The GENE POOL of a population
CHANGES in favor of the “FITTEST”
phenotype & genotype!!!
nvironment selecting “good” traits for THAT environme
Example: Peppered Moth
Sampling the birds that died as well
as those that survived showed that
•the larger birds were favored
over the smaller ones
•those with larger beaks were
favored over those with smaller ones.
of Small beaks
From 1976 through 1977, a severe drought struck an island in the Galapagos.
Some phenotypes are more fit than others when it comes to
competing for resources. The more “FIT” phenotype will
survive and have the possibility of passing its alleles to the
• James Hutton -1785-Proposed
that the Earth is millions of years
• Many land formations took millions
of years to form.
• Known as the founder of modern
• Thomas Malthus -1798• Proposed that populations outgrew
their food supplies, causing
competition between organisms and a
struggle for one species to survive against
• This "struggle for existence" drives
-1809• Believed that all life
forms evolved and that
the driving force of
evolution was the
inheritance of acquired
• He believed that
organisms changed due
to the demands of their
•Charles Lyell -1830-proposed
that plant and animal species had
arisen, developed variations, and
then became extinct over time.
•He believed that every animal or
plant, including humankind, was
the present is the key to
adapted to the niche in which it
understanding the past
•He also believed that
the Earth’s physical
landscape changed over
a long period of time.
• Alfred Russel Wallace -
• Emphasis was based on the
idea of competition for
resources as the main force
in natural selection.
Best known for independently
proposing a theory of natural
selection which prompted Charles
Darwin to publish on his own theory
• Charles Darwin -1859-
Publishes “On the Origin of
• Believed that Natural Selection
is the driving force for
Summary of Darwin’s Ideas
1. Individual organisms differ, and
some of this variation is heritable.
2. Organisms produce more offspring than can
survive, and many that do survive do not
3. Because more organisms are produced than
can survive, they compete for limited
4. Individuals best suited to their environment
survive and reproduce most successfully.
Summary of Darwin’s Ideas
5. These organisms pass their heritable
traits to their offspring. Other
individuals die or leave fewer offspring.
6. This process of natural selection causes
species to change over time.
7. Species alive today are descended with
modification from ancestral species that lived
in the distant past.
8. This process, by which diverse species evolved
from common ancestors, unites all organisms
on Earth into a single tree of life.
Review Clip: 10min
Whale Video Clip- Intro to
evidence ( Questions in packet)
Evidence for Change Over Time
– Fossils that show
how the same
millions of years
– Use rock layers
– 1) Isotope dating
2) Relative Dating
Analogous versus Homologous Structures
– Organs or
do not seem to
be used by the
– They are
are all a
• The numbers
number of amino
between the beta
chain of humans and
the hemoglobins of
the other species.
• In general, the
number is inversely
proportional to the
closeness of kinship.
• Organisms that are related change/adapt
according to their environment.
• The evolution of many
diversely adapted species
from a common ancestor
– Relatively rapid
• Usually occurs when a
population colonizes an area of
diverse geographic or
– New niches
a different set
How do we get new species?
Where do new species come
Species: population whose members can interbreed in
nature and produce viable, fertile offspring
Evolution: change in the allelic
frequencies in a population
In the physical world, natural barriers form
and cause the breakup of populations to form
Volcanoes, sea-level changes, and
earthquakes are a few examples of natural
occurrences that affect populations
• Geographic Isolation
– Separated by bodies of water or mountains.
• Temporal Isolation
– Reproduction takes place at different times of the year
– Different Mating seasons
•Overtime they can change so much that they
become unable to breed as they adapt to their
–Populations are capable of interbreeding, but have
different courtship rituals or other type of behavior.
–Do not recognizes another species as a mating partner.
–Brightly colored male- drab female
– video clip: Dressing fro desire
•A population is a localized
group of individuals that belong
to the same species.
Genetic drift— along with natural selection, mutation, and
migration—is one of the basic mechanisms of evolution. 57
Changes in allele frequency with in a population
Start Packet #2
• Review Clip
Two or more related species becoming more and
development of similar
development of similar
Bumblebees & the flowers they
pollinate have coevolved so that
both have become dependent on
each other for survival.
• Some Central American Acacia species have hollow thorns and pores at
the bases of their leaves that secrete nectar. These hollow thorns are
the exclusive nest-site of some species of ant that drink the nectar. But
the ants are not just taking advantage of the plant—they also defend
their acacia plant against herbivores.
Evolution at the species level is
It results from genetic variation
and natural selection within a
population of organisms.
Macroevolution is evolution that
occurs between different
Evolution is the
change in a
Rates of Evolution
Gradualism & Punctuated Equilibrium
• Two ways in
evolution of a
• A species can
only one of
these, or by
•Species with a shorter evolution evolved mostly by
punctuated equilibrium, and those with a longer
evolution evolved mostly by gradualism.
•Very gradually, over a long
time... Over a short period
of time it is hard to notice.
•Small variations that fit an
organism slightly better to
its environment are selected
for: a few more individuals
with more of the helpful
trait survive, and a few
more with less of the
helpful trait die.
•Change is slow, constant,
•change comes in spurts. There
is a period of very little change,
and then one or a few huge
changes occur, often through
mutations in the genes of a few
• STOP HERE>>>>>>>>>>>>>
• When organisms are no longer
affected by a drug.
• First documented around 1952
• Causes: Natural consequence
of selective pressures in the
Resistance in Bacteria
Read page p403.
• Bacteria- Antibiotic
• Many insects have
Types of Selective Processes in Natural Selection
Intermediate forms of a
trait are favored and
alleles that specify
extreme forms are
eliminated from a pop.
Ex: Human birth weight
stay between 6-8 lbs.
Lower or higher has
Changing environmental conditions give rise to
directional selection, where one phenotype
replaces another in the gene pool.
Can produce rapid shift in allelic frequencies.
Ex: Peppered moth
– peppered moths, pesticide resistance,
Occur in response to:
* directional change in the environment
* one or more new environmental conditions
* a mutation that appears and proves to be adaptive
extreme types in
a population at
the expense of
divided into two.
(bill size in seedcrackers)
• Diversifying selection can result in balanced
• For example, two distinct bill types are present in
black-bellied seedcrackers in which larger-billed
birds are more efficient when feeding on hard seeds
and smaller-billed birds are more efficient when
feeding on soft seeds.
• Exists when a heterozygote
(Aa) has a higher fitness than
either homozygote (AA, aa).
• ex: Sickle Cell
• The term given to an evolutionary
process where the fitness of a
phenotype is dependent on its
• Can arise in systems of mimicry
– ex: Butterflies
• ex: Maintenance of a 50:50 sex ratio:
If one sex becomes more common,
some of its members will not be able
• Adaptation is a key concept
in natural selection.
• Natural selection can change
the inherited characteristics in
a population and possibly
even result in a new species.
Two main sources of genetic
2.Genetic Shuffling (by sexual
It is important that you are able to
explain how the concepts of genetics provide the basis
for explaining natural selection and evolution. This will
help you answer questions like this:
What is the end result of natural
A increased number of offspring of a given
phenotype that survive
B changes in the frequency of alleles in a
C fossil formation through extinction
D environmental changes of a habitat
Although the Arctic fox and the kit fox are closely related,
they look very different because the individuals
A acquired traits during their lifetimes that contributed to
B with traits most suited to their environments reproduced most
C migrated long distances to environments that most suited
D passed on to their offspring acquired behaviors that were
Fossils of Archeopteryx show that this animal had feathers, like 91
bird. It also had a bony tail, teeth, and claws on its
like a reptile. This fossil is evidence that supports the idea that
A. birds and reptiles have a common ancestor
B. birds have changed very little over 150 million
C. reptile species are more advanced than bird
D. reptiles are warm-blooded like birds
Horses and tapirs have a common ancestor, but now look
very different. Horses now are grassland animals adapted for
grazing on grass and shrubs. Tapirs are jungle animals that
live in dense forests and eat fruit, leaves and aquatic
vegetation. Which of the following led to the development of
such differences in the two species?
A selective breeding
B convergent evolution
C DNA hybridization
D natural selection
Adaptation is the key
concept in natural