Chapters 15-17
Evolution
Science Definitions
Theory
• A well-substantiated explanation of some
aspect of the natural world that typically
incorporates many confirmed
observations, laws and successfully
verified hypotheses.
Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html
Evolution
• Book definition = Gradual accumulation
of adaptations over time.
• In genetic terms, the change in the
frequency of alleles in populations from
generation to generation. (change over
time)
Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html
Adaptation
• Any heritable characteristic (determined
from alleles) of an organism that
improves its ability to survive and
reproduce in its environment.
• Note: not all characteristics are adaptive
Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html
Adaptations
http://animals.nationalgeographic.com/
Fitness
• The success of an individual in surviving
and reproducing, measured by that
individual’s genetic contribution to
subsequent generations.
Modified from http://www.pbs.org/wgbh/evolution/library/glossary/index.html
Natural Selection
• Charles Darwin’s Theory
• Mechanism for change in populations.
• Occurs when organisms with certain
traits survive, reproduce and pass their
variations to the next generation.
• “Survival of the Fittest”
Natural Selection
1. Variations exist in a population
Natural Selection
2. Some variations improve the ability to
survive and reproduce in the particular
environment
Sweet! I’m better at
surviving because I
blend into my
surroundings!
Dang!
Natural Selection
3. The individuals with the adaptive traits
are more likely to pass on their genes to
Dang!
future generations
I have more
fitness than
you!
Natural Selection
4. Over time, the frequency of adaptive
alleles increases = evolution.
The Four Tenants of Natural
Selection…
1. OVERPRODUCTION: Organisms produce more offspring
than their environment can support.
2. HERITABLE VARIATION: Offspring vary in their
appearance and function; some of these variations are
heritable.
3. COMPETITION: Offspring must compete for survival,
food and reproduction.
4. SURVIVAL OF THE FITTEST: Offspring who have the
highest fitness for their environment will live longer
and/or leave more offspring than those less suited for
the environment.
Can we see natural selection in one
generation?
• No…
• This process occurs very slowly, over many
generations
• Natural selection can only be observed as
changes in the characteristics or behaviors in
populations over time.
Natural Selection…
Caterpillars… what is the benefit of looking like bird poop?
Overproduction & Heritable
Variation in butterflies…
• How many offspring do butterflies produce?
• 1000+ offspring … not that many survive
• What kind of variation could we see in larva (caterpillars)?
• Different color patterns
• Different sizes
• Diet
• Is this variation in color patterns heritable?
• Genes control color patterns in all organisms…
• Offspring from a butterfly (caterpillar) that was green as a larva?
• Offspring from a butterfly (caterpillar) that was brown and white as a
larva?
Competition & Survival of the
Fittest…
• Caterpillars have competition for food, survival &
reproduction.
• Who will survive the longest?
– Best camouflage = less likely to be seen by predators =
longer survival = more reproduction
• If those that look like bird poop survive longer, what will the
population start to look like over many generations?
– Like bird poop!
• NATURAL SELECTION – the natural selection of characteristics
that allow an animal to survive and reproduce (sometimes
because of their ability to blend in with their environment)–
makes them more fit.
Other examples of selection for
survival…
Natural Selection…
Cheetahs… why can they run so fast?
Overproduction & Heritable
Variation in cheetahs…
• How many offspring do cheetahs produce?
• 5-6 offspring per year … not that many survive
• What kind of variation could we see in cheetahs?
•
•
•
•
Size of the heart
Length of the legs
Color patterns
+ many others
• Is this variation in length of legs heritable?
• Genes control color length of limbs in all organisms…
• Offspring from a cheetah with long legs?
• Offspring from a cheetah with short legs?
Competition & Survival of the
Fittest…
• Cheetahs have competition for food, survival & reproduction.
• Who will survive the longest?
– Those that can run fast enough to catch prey to survive =
longer survival = more reproduction.
• If those that look run faster eat more, what will the
population start to look like over many generations?
– Fast runners!
• NATURAL SELECTION – the natural selection of characteristics
that allow an animal to get more food within their
environment – makes them more fit.
Sexual Selection…
The male peacock… why waste so much energy producing feathers?
Overproduction & Heritable
Variation in peacocks
• How many offspring do they produce?
– 6-8 per year are hatched… not that many survive
• What kind of variation could we see in male peacocks?
– Different color patterns
– Different feather sizes
– Size of bird
• Is this variation in feather size heritable?
– Genes control how large feathers will get…
• Offspring from a peacock with large feathers?
• Offspring from a peacock with short feathers?
Competition & Survival of the
Fittest…
• Peacocks have competition for food, survival & reproduction.
• Who will reproduce the most?
– Largest feathers = more reproduction
• If those with large feathers reproduce more, what will the
population start to look like over many generations?
– Larger feathers, on average.
• SEXUAL SELECTION – the natural selection of secondary sex
characterizes in males is WORTH the energy they spend
because it increases levels of reproduction – makes them
more fit.
Other interesting secondary sex
characteristics….
Natural Selection in the last few
years…
Antibiotic Resistance
AZT-Resistant HIV (AIDS virus)
AZT-Resistant HIV (AIDS virus)
Resistance to AZT has evolved in all patients
taking the drug (usually in ~6 months)!
How does HIV evolve so rapidly?
1. High mutation rate
• HIV’s mutation rate is 106 higher than ours!
2. Short generation time
• 1 year ≅ 300 viral generations.
10 years of viral ≅ 2-3 x 106 years of human evolution!
Bt-resistant Cotton Bollworm
Natural Selection
Last week we did a lab demonstrating
natural selection… you just didn’t know
about it.
?
Assignment #1
• Complete the following chart using pages 398
& 399
Definition
Directional
Selection
Stabilizing
Selection
Disruptive
Selection
Example
Picture
Assignment #2
• Complete the following chart using pages 404
& 405
Definition
Behavioral
Isolation
Geographic
Isolation
Temporal
Isolation
Example
Picture
Speciation
The first steps of speciation have been
produced in several laboratory experiments
involving “geographic” isolation. For example,
Diane Dodd took fruit flies from a single
population and divided them into separate
populations living in different cages to simulate
geographic isolation. Half of the populations
lived on maltose-based food, and the other
populations lived on starch-based foods. After
many generations, the flies were tested to see
which flies they preferred to mate with. Dodd
found that some reproductive isolation had
occurred as a result of the geographic isolation
and selection in the different environments:
“maltose flies” preferred other “maltose flies,”
and “starch flies” preferred other “starch flies.”
Speciation
• One species splits into two due to
isolation (geographic, reproductive, etc…)
• Also known as Divergent Evolution…
results in homologous structures
between groups
Speciation
Hurricane
http://evolution.berkeley.edu
Speciation
The populations diverge: Ecological conditions are slightly different on the island,
and the island population evolves under different selective pressures and
experiences different random events than the mainland population does. Morphology,
food preferences, and courtship displays change over the course of many
generations of natural selection.
http://evolution.berkeley.edu
Speciation
So we meet again: When another storm reintroduces the island flies to the mainland,
they will not readily mate with the mainland flies since they’ve evolved different
courtship behaviors. The few that do mate with the mainland flies, produce inviable
eggs because of other genetic differences between the two populations. The lineage
has split now that genes cannot flow between the populations.
http://evolution.berkeley.edu
Speciation
http://evolution.berkeley.edu
Some Evidence of Evolution
•
•
•
•
Geographic Locations
Anatomical Similarities
Developmental Similarities
Molecular (biochemical) Similarities
Some Evidence of Evolution
• Geographic Locations
Some Evidence of Evolution
• Anatomical Similarities
–Homologous Structures = structural
features with a common evolutionary
origin. Similar in arrangement,
function or both.
Some Evidence of Evolution
• Anatomical Similarities
–Homologous Structures
Some Evidence of Evolution
• Anatomical Similarities
–Homologous Structures
http://www.ucmp.berkeley.edu/
–Analogous Structure = A structural or
functional similarity of a body feature,
but not related.
Example: Insect
& bird wings are
similar in function,
but not structure
Some Evidence of Evolution
• Anatomical Similarities
–Vestigial Structures = a body structure
that has no function in a present-day
organism but was probably useful to an
ancestor.
Some Evidence of Evolution
• Anatomical Similarities
–Vestigial Structures
Some Evidence of Evolution
• Developmental Similarities
–Comparative embryology
• Early developmental stages are compared.
• Related embryos look similar.
• Page 410 (bird, deer, human) Look for tails
and gill slits.
Some Evidence of Evolution
• Developmental Similarities
–Comparative embryology
Some Evidence of Evolution
• Molecular (biochemical) Similarities
Some Evidence of Evolution
• Molecular (biochemical) Similarities
Some Evidence of Evolution
• Anatomical Similarities
–Fossils
• Evidence of an organism that lived long ago.
• Most fossils are found in Sedimentary rock.
• 6 types (page 378)
http://www.earthhistory.org.uk/wp-content/crayfish.jpg
1. Trace Fossils
https://courseware.e-education.psu.edu/courses/earth105new/graphics/L02_fossil_hpl922.jpg
2. Casts
http://www.activityvillage.co.uk/cast-fossils.jpg
3. Imprints
http://www.hopefossils.co.uk/Fossil%20photos/Trilobite%20under%20x10%20magnification%20-%20Placoparia%20cambriensis.JPG
4.Amber-Preserved & Frozen
http://dsc.discovery.com/news/2007/10/08/gallery/amber_zoom.jpg
5. Petrified
http://www.legendsofamerica.com/photos-arizona/PetrifiedWood.jpg
6. Molds
http://www.ammonoid.com/mcE-m.jpg
Geologic Time Scale – Page 421
Notice the short amount of time that humans have been a part of Earth’s history.
http://www.life.illinois.edu/mcb/419/images/GeoTimeSpiral.jpg
Phylogeny
Figure 1: A diagram of Mimi's immediate family. The passage of genes from
parents to offspring is indicated by the green lines.
Figure 2: The genetic relationships for the last three generations of beetles
under Mimi's log.
Figure 3: Genetic relationships for a segment of Mimi's beetle population over a
number of generations. The last three generations of beetles under Mimi's log are
shown in the blue frame.
Figure 4: Genetic relationships between two closely related species, Bembidion
levettei and Bembidion zephyrum. Recent generations of beetles in Mimi's
species are indicated with the blue frame. The arrow points to the common
ancestor of the two beetle species.
Figure 5: A phylogenetic tree of beach beetles. Some branches have gone extinct
in the past, while others represent species living today.
Figure 6: Genetic connections flowing along the branches of the Tree of Life.
???
Figure 7: The Tree of Life that we’ll be using for the rest of the semester.