Unit 11 - Evolution
Part 1: Principles of Evolution –
Evolution by Natural Selection
(Ch. 10 Sec. 1-5, Ch. 12 Sec. 1 & 2)
Evolution Part 1
Principles of Evolution—Evolution by Natural Selection
(Ch. 10 Sec. 1-5, Ch. 12 Sec. 1 & 2)
• Look at the star-nosed mole.
(p. 285)
What sorts of modifications are
obvious?
1.
– Ray-like feelers extending from snout,
poor eyesight, and prominent claws
2. How might these traits arise in the first place?
--Mutations in DNA
– These mutations will then be passed on to future
generations.
What is Evolution? (Ch. 10.1-10.2)
Evolution
• Evolution is change in species over time
• Process of biological change by which
descendants come to differ from their
ancestors (p. 286)
• Change happens in characteristics of a
population from one generation to the next
• Populations evolve, individuals do not!
Name things that have changed
over time
Example: Radios
Vocabulary
• Population – all of the
individuals of a species
that live in an area
(p. 294)
• Variations – differences
in the physical traits of
an individual from
those traits of
individuals in the
population
Vocabulary
• Species – group of organisms are
that are closely related and can
mate to produce fertile offspring
– Dogs (Canis familiaris) are all the same
species; just like all modern humans are
all Homo sapiens.
– We have different dog breeds based on their genetic
variations but they are all the SAME species. No two
people look exactly alike due to genetic variation within
the human population
• Speciation – process in which new species are
formed over time
Vocabulary
• Adaptation – a feature that allows an organisms to
better survive and reproduce in its environment; this
can lead to genetic change in a population over time.
Charles Darwin – the father of evolution
(p. 290-291)
• born in 1809, in England
• was asked to sail on the
H.M.S. Beagle to chart
stretches of the South
American coast
Charles Darwin – the father of evolution
(p. 290-291)
This voyage lasted from 1831 to 1836.
Charles Darwin –
the father of evolution
(p. 290-291)
• Voyage of H.M.S. Beagle
– 5 year unpaid voyage
– Darwin studied plants, animals, collected fossils
– found fossils of extinct animals that were similar
to modern species.
– during his voyage, he made observations that led
him to his theory of evolution.
Charles Darwin –
the father of evolution
(p. 290-291)
On the Galapagos Islands in the Pacific
Ocean he noticed many variations
among plants and animals of the
same general type as those in South
America.
Darwin noticed there were several
types of finches on these islands, and
that they all looked like a bird he had
seen on the South American
continent.
Charles Darwin – the father of evolution
(p. 290-291)
• The most distinct difference among finch species
is their beaks
• Why would beaks be different in different
locations on an island?
– they are adapted for the
specific diets available
on the islands.
Charles Darwin – the father of evolution
(p. 290-291)
• Darwin hypothesized that
some of the birds from
South America migrated
to the Galapagos
• once on the islands, the
birds must have changed
over the years, explaining
the numerous species of
birds present
Charles Darwin – the father of evolution
(p. 290-291)
• After returning from the Galapagos and studying
all the different types of plants & animals he
collected during the voyage, Darwin concluded
that organisms change over time.
– Darwin called this evolution, which means change in
species over time.
– Darwin called the mechanism for evolution natural
selection (a.k.a. survival of the fittest).
How does Evolution Happen?
•
•
•
•
•
•
Natural Selection
Mutations
Artificial Selection
Geographic Separation/Isolation
Genetic Drift
Gene Flow (migration)
Natural Selection – the main
mechanism of evolution (Ch 10.3 & 11.2)
• Natural selection explains how evolution can occur.
• natural selection – a mechanism by which
individuals that are better fit for their environment
have a greater chance to survive and
mate/reproduce (p. 293)
– aka- Survival of the fittest
– What does it mean to be “fit”?
• fit means they have inherited beneficial adaptations which
allow them to be more likely to survive and reproduce more
offspring.
– the genetic traits of “fit” individuals become more
common or frequent over time.
– The genetic traits of less fit individuals become less
common or frequent over time.
There are four main principles to the
theory of natural selection
1. Variation – heritable differences that exist in
populations
2. Overproduction – not all offspring will survive
due to competition
3. Adaptation – certain variations can allow an
individual to survive better than others (the
environment can present challenges for survival)
4. Descent with Modification – the number of
individuals with the advantageous adaptations
will increase over each generation
• A well-studied example of natural selection in
jaguars is shown in Figure 3.2 p. 295
• View animated biology – 10.3 Principles of
Natural Selection (Jaguar)
Example: Natural Selection and beetles
– beetles have genetic variation
✓ Some are brown, others green
– there is a struggle for survival
✓ Predation
– more fit individuals leave more offspring
--characteristics of fit individuals
increase in a population over time
What would happen if the environment
changed from brown stones to green grass?
Natural Selection acts on existing variation
• Natural selection can only act on traits that
already exist.
• Natural selection acts on phenotypes; new
alleles occur by genetic mutations.
– Read p. 296-297 about the 2 examples supporting this
concept.
– View Animated Biology
10.3 Natural Selection
(fish) (may not work in
Chrome; works best
in Safari)
Artificial Selection (p. 292)
• Artificial Selection – the process by which
humans change a species by breeding it for
certain traits
– Humans determine which traits are favorable and
breed individuals that show those traits.
– Ex. race horses, show dogs
Unit 11
Part 2: Evidence to Support Evolution
(Ch. 10.4-10.5, Ch. 12.1)
Evidence to Support Evolution
(Ch 10.4-10.5, Ch. 12.1)
• Evidence to Support Evolution:
– fossil record (p. 298, 306, 348)
– Biogeography
– Homologies : anatomy, development & molecular
(p. 299-304)
Fossil Record (Ch 10.4 & 12.1)
• What is a fossil?
– Fossil – trace of a
dead organism
– Scientists consider
three things about
fossils: age, location
and what the
environment was
when that organism
was alive.
– Fossils are dated
through radiometric
dating and relative
dating.
Fossil Record
• Radiometric dating uses
the known time of
natural decay of unstable
isotopes to calculate the
age of the material.
• Relative dating estimates
the age of fossils by
comparing the fossils
found in certain rock layers
to those in other layers. The oldest fossils are
found on the bottom, further from the surface.
The youngest fossils are closest to the surface.
Fossil Record
• Fossils can form in several ways (p. 298, 306,
& 348). The most common fossils result from
permineralization.
Fossil Record
• What may happen if the organism doesn’t die
in sediment?
– Fossil doesn’t form; decomposition takes place
• Why is the fossil record not complete?
– Most living things do not form into fossils when
they die since the conditions are not conducive to
fossil formation
– Many fossils may not have been discovered yet
Biogeography (p. 299)
• biogeography - Is the study
of the geographic
distribution of plants,
animals and fossils.
– it is used to test predictions
about the nature, age, and
location of certain fossils.
– species tend to be more
closely related to other
species from the same area
than to other species with the
same way of life but living in
different areas.
Anatomy and Development (p. 299-304)
homologous structures (p. 302)
• homologous structures:
- common ancestor
- Similar structure
- Different function
• Example: the long bones of a cat, human,
whale and bat are similar in structure
(made of bones) but have different functions.
Homologous Structures
– Similar Structure
– Different Function
– Common Ancestor
Forelimbs of Vertebrates
Anatomy and Development (p. 299-304)
• analogous structures p. 303
– not related
– different structures
– same function
• examples:
– bird wing and
insect wing
Analogous Structures - Quills
Hedgehog (mammal)
Cactus (plant)
• not related
• different structures
• same function
Sea urchin
(invertebrate)
Anatomy and Development
(p. 299-304)
• vestigial structures p. 304
• vestigial structures- serve
no useful purpose.
• examples:
– pelvic bone in a whale
– human appendix
– pelvic bone & hind limb bones
in some snakes
- human canine teeth & wisdom
teeth
Vestigial
Structures
cont’d
Examples of Vestigial Structures
• Extra pad and nail on dog & wolf paws
Vestigial Structures (cont’d)
Eyespot on a
cave
salamander.
This little guy
NEVER sees
light.
Embryology
(p. 299-39)
• Embryology - Similarities
in embryological
development among
organisms is further
evidence of shared
common ancestry
• Ex. Crab and barnacle
– adults look very
different but the larva
can look very similar
(Fig 4.4)
• Ex. Embryos of vertebrates
Molecular Evidence (p. 307)
– Very different species have similar molecular
and genetic mechanisms. Because all living
things have DNA (bacteria, plants, animals,
etc.), they share the same genetic code and
make most of the same proteins from the
same 20 amino acids.
– More similarities in DNA (which translates
into proteins) between two organisms, the
more closely related they are, the more
differences; the more distantly related.
Molecular Evidence (p. 307)
• Comparing Amino Acids
1. Which organism is most closely related to the
human? Why? Chimpanzee; greatest number of
similarities with human
2. Which organism is least closely related to the
human? Why? Kangaroo; greatest number of differences
when compared too human
Number of amino acids that differ from
a human
Molecular Evidence (p. 307)
• Remember, the DNA
sequence dictates the
amino acid sequence
through the processes
of transcription and
translation, therefore,
ALL 4 levels (DNA,
RNA, amino acids, and
proteins) can show
evidence of evolution
Molecular Evidence (p. 307)
• Watch Hox genes video clip (2:44) Section 10.5
“Evolutionary Biology 1” in your online textbook
– Sign in to Google or gmail; then go to the online
textbook
– Select Chapter 10 in dropdown box and click “GO”
– Click on Student Resources
– Click on Videos
– Click on Biology Video Clips
– Click on
Section 10.5 “Evolutionary Biology 1”
Unit 11
Part 3: The Evolution of Populations
(Chapter 11)
Genetic Variation Within Populations
(p. 316-321)
Vocabulary
• gene pool – combined
alleles of all the
individuals in a
population
Vocabulary
• alleles – different forms of a gene
– flower color gene may be
“P” (purple) or “p” (white)
• frequency – how often something occurs over
time
– Ex. If 25 rabbits are white, out of a population of 100
rabbits, the frequency of white rabbits is 0.25
Genetic Variation Within Populations
(p. 316-321)
• Genetic variation in a population increases the
chance that some individuals will survive.
• Genetic variation comes from two main sources.
– Mutation - random change in the DNA of a gene; if
the change occurs in the DNA of a reproductive cell
(gamete=egg or sperm), then the mutation will be
passed on to offspring.
– Recombination – new allele combinations in an
offspring that occurred during meiosis through
crossing over and independent assortment.
Other Mechanisms of Evolution
(p. 323-327)
• Natural selection isn’t the only mechanism
through which populations evolve. Other
mechanisms include: genetic drift, gene flow,
mutation and sexual selection.
Other Mechanisms of Evolution (p. 323-327)
gene flow – movement of alleles from one population
to another
Population 1
Population 2
Population 2 over time
Individuals in Population 1 migrate to Population 2 and change the frequency of green beetles
found there
Other Mechanisms of Evolution (p. 323-327)
• another word for gene flow is migration
(immigration & emigration)
• gene flow increases the genetic variation of the
receiving population
• lack of gene flow
between two
populations may
lead to the
formation of
different species
Other Mechanisms of Evolution (p. 323-327)
Genetic Drift
• genetic drift - change in allele (gene) frequency
due to chance; results in loss of diversity
• Two types of genetic drift
1. Bottleneck effect
2. Founder effect
Other Mechanisms of Evolution (p. 323-327)
Genetic Drift
o Bottleneck effect when a population is
drastically decreased
due to a natural
disaster (hurricane,
disease)
• some genes are
completely lost; others
are over-represented
• some genes are reduced so much they can’t “make
a come back” in their new population
Other Mechanisms of Evolution (p. 323-327)
Genetic Drift
o founder effect – when a small group splits off
from a larger population and starts their own
population isolated from the original population
• Amish in America – original population was 14
individuals that immigrated from Europe
Other Mechanisms of Evolution (p. 323-327)
Mutations
• a random mutation can happen to one individual
in a population, and can ge beneficial, harmful,
or neutral
• random mutations can increase chances of
survival and reproduction
Other Mechanisms of Evolution (p. 323-327)
• random mutations can decrease chances of
survival
– if an individual
dies before it
can reproduce,
that mutation
is not passed
down to
another
generation
Other Mechanisms of Evolution (p. 323-327)
• random mutations
might not affect an
individuals ability to
survive and reproduce
and will become a
natural variation
instead of a mutation
• Ex. dark spots on pigs
Sexual Selection (p. 326)
• Sexual selection occurs when certain traits
increase mating success.
• Ex. Males compete for females such as the
head-butting of bighorn sheep; Male
peacocks fan out their tails to attract the
female.
Hardy-Weinberg (p. 328)
• 1908 - two scientists created an equation to test these ideas of
probability and chance
• Hardy-Weinberg principal - the frequency of alleles in a population
does not change unless evolutionary forces act on the population
• Characteristics of a Hardy-Weinberg (non-evolving)
population:
-
very large population
-
no migration (no immigration or emigration)
-
no mutations
-
random mating (no individual are “more fit”, they all seem to the same)
-
no natural selection
● A population with all of these criteria is not evolving. This doesn’t
happen in nature; therefore all populations in nature are evolving.
Isolation of a population can lead to speciation
(p. 332)
• Reproductive isolation –when members of different
populations of the same species can no longer mate
successfully.
• Reproductive isolation can lead to speciation.
• Three barriers that can cause reproductive isolation to
occur:
1.
2.
3.
Behavioral barriers – courtship or mating behaviors are now
different in the population
Geographical barriers – physical separation of the populations;
Ex. mountains, roads, rivers
Temporal barriers – the two populations aren’t ready to mate
at the same time of day (ex. Flowers that bloom in morning vs.
evening) or in the same season
Patterns of Evolution (p. 335-341)
Convergent evolution (word part: co = together)
similarities not because they are related but
because they need certain adaptations to
survive in their environment; therefore, they
have analogous structures
Patterns of Evolution (p. 335-341)
Convergent evolution
• Example:
• Sharks, dolphins, tuna, penguins have
streamlined bodies, and fins.
• HOWEVER Sharks are cartilaginous fish,
dolphins are mammals, tuna are bony
fish, and penguins are birds.
• they share similarities because they all
adapted to the same marine
environment and predatory lifestyle.
Convergent evolution is sometimes called parallel
evolution
Patterns of Evolution (p. 335-341)
• Divergent evolution
(word part: di = two);
the process by which
one species begins to
split into two distict
groups with different
traits; therefore, they
have homologous
structures
Patterns of Evolution (p. 335-341)
Divergent evolution
Example:
• All canines have long legs, walk on their toes, non-retractable claws,
and dew claws because they all come from a common ancestor.
• Different populations diverged at different points an created all these
species (domestic dogs, wolves, coyotes, foxes, etc.)
Divergent evolution is sometimes called adaptive radiation and may lead to
speciation.
Phylogenic (or Phylogenetic) Tree
• a diagram
showing the
evolutionary
history of a
species of an
animal.
• Is this
convergent or
divergent
evolution?
Divergent
Patterns of Evolution (p. 335-341)
Coevolution – process in which two or more
species evolve in response to changes in each other.
Ex. ant and acacia tree, crabs & snails,
flower structure & bird beak shape (p. 337)
Patterns of Evolution (p. 335-341)
Extinction – elimination of a species, usually as
a result of its inability to adapt to a change in
the environment; Ex. dinosaurs (p. 338)
Patterns of
Speciation
(p. 339)
• gradualism- slow
changes happen
continuously over
a long period of
time
– Ex. Evolution of the
horse (p. 339)
Patterns of Speciation (p. 339)
• punctuated equilibrium- bursts of rapid
change in species are separated by periods of
little to no change
– “spurts in evolution”
– traits “appear suddenly” in the fossil record
usually due to climate changes or catastrophic
events
Gradualism vs. Punctuated Equilibrium
In Summary…
• Life forms reproduce and therefore have a
tendency to become more numerous.
• The offspring differs from the parent in minor
random ways.
• If the differences are helpful, the offspring is
more likely to survive and reproduce.
• This means that more offspring in the next
generation will have the helpful difference.
• These differences accumulate resulting in
changes within the population.
• Over time, populations branch off to become
new species as they become separated.
• This process is responsible for the many
diverse life forms in the world.
• Haeckel's Paleontological Tree of Vertebrates
(c. 1879).