chapters 15-17

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)


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


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.


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 future generations

I have more fitness than

you!

Dang!

Natural Selection

4. Over time, the frequency of adaptive alleles increases = evolution.

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.

*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.

• Is there any variation in pinto beans???

Bean Variation Mini-Lab1. Create Data Table with two three columns:

Bean Number, Mass (g), and Qualitative Observations

2. Work with a partner and choose 10 random beans from the beakers at your station. Try not to be selective for any properties whatsoever

3. Measure each bean’s mass and record, along with qualitative observations

4. Share your data with two other groups to get a total of 30 beans recorded.

Bean Variation Mini-Lab4. In your journal, create a frequency distribution

graph as modeled on the whiteboard. For the x-axis, use bean mass (g), and put number of beans on the y-axis

Answer the following questions in your journal:1. How does your graph compare to the overall class

data?2. What factors do you think are responsible for

causing the variation in the pinto beans?3. What could be advantages of being bigger or

smaller for a bean seed? Identify several.

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 length of limbs …

• Offspring from a cheetah with long legs?• Offspring from a cheetah with short legs?


• 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 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?


• 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 recent years…

Bt-resistant Cotton Bollworm

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 10≅ 6 years of human evolution!

Natural Selection

Over the past few weeks we did a lab demonstrating natural selection… you just didn’t know about it.

??

What is a species?

A group of interbreeding populations that cannot breed with other groups.

Giraffes and Elephants?German Shepards and Poodles?

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.


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.


Speciation

Because of “geographic” isolation,“maltose flies” preferred other “maltose flies,” and “starch flies” preferred other “starch flies” when choosing mates

Speciation

• One species splits into two due to isolation (geographic, reproductive, etc…)

• Also known as Divergent Evolution… results in homologous structures between groups

Speciation


Direction of Natural Selection and Species Formation

• Stabilizing – extremes not favored (example – human birth weight)

• Disruptive – extremes favored (example - short or long beaks not medium beaks)

• Directional – extremes at one end favored

Isolation

• Geographic Isolation: separated by a physical barrier of some kind

• Behavioral Isolation: Differences in courtship displays prevent reproduction

• Temporal Isolation: separated by differences in the timing of reproduction

Genetic Drift

• Random changes in numbers of individuals in a population can lead to allele frequency changes in a population

• This is called Genetic Drift

Assignment #1• Complete the following chart using pages 398

& 399DefinitionDefinition ExampleExample PicturePicture

Directional Selection

Stabilizing Selection

Disruptive Selection

Assignment #2• Complete the following chart using pages 404

& 405

DefinitionDefinition ExampleExample PicturePicture

Behavioral Isolation

Geographic Isolation

Temporal Isolation

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

Some Evidence of Evolution• Geographic Locations• Anatomical Similarities• Developmental Similarities• Molecular (biochemical) Similarities

Some Evidence of Evolution• Geographic Locations (and Convergent

Evolution)

Convergent Evolution – when species become more alike

• Animals live apart but in similar environments

• Desirable traits are same

• Example – rabbit and squirrel color

Some Evidence of Evolution• Anatomical Similarities

–Homologous Structures = structural features with a common evolutionary origin (inherited from same common ancestor). Similar in arrangement, function or both.


–Homologous Structures—inherited from the same ancestors

Not the same thing as…–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*Instead, this would demonstrate convergent evolution


–Can also be seen in fossils• Evidence of an organism that lived long ago. • Most fossils are found in sedimentary rock. • Many different types

http://www.earthhistory.org.uk/wp-content/crayfish.jpg

Trace Fossils

https://courseware.e-education.psu.edu/courses/earth105new/graphics/L02_fossil_hpl922.jpg

Imprints

http://www.hopefossils.co.uk/Fossil%20photos/Trilobite%20under%20x10%20magnification%20-%20Placoparia%20cambriensis.JPG

Cast/Molds

http://www.ammonoid.com/mcE-m.jpg

Petrified

http://www.legendsofamerica.com/photos-arizona/PetrifiedWood.jpg

Amber-Preserved & Frozen

http://dsc.discovery.com/news/2007/10/08/gallery/amber_zoom.jpg

Some Evidence of Evolution• Fossils can show

homologous structures• Pteranodon—same sequence

of bones in forelimb as other vertebrates, suggesting common ancestry

http://www.ucmp.berkeley.edu/


–Homologous StructuresArchaeopteryx—shared

characteristics of reptiles and birds (e.g. teeth and feathers). “Transitional species” with homologous structures to existing species can suggest possible common ancestry of two different groups


–Vestigial Structures = a body structure that has no function in a present-day organism but was probably useful to an ancestor.


–Vestigial Structures

Some Evidence of Evolution• Developmental Similarities

–Comparative embryology• Early developmental stages are compared.• Related embryos look similar, suggesting

common use of the same hox genes during development

Some Evidence of Evolution• Developmental Similarities

–Comparative embryology

Some Evidence of Evolution• Molecular (biochemical) Similarities

Geologic Time Scale – Page 421Notice 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

chapters 15-17

Documents

competition survival

longer survival

survival reproduction

color patterns heritable

heritable characteristic

natural world

natural selectioncaterpillars

natural selection3