EW: Why do organisms evolve? Is it their choice to change?

Monday, May 12th, 2014

• LT: I will be able to discuss the mechanisms of evolution.

Agenda: -What is evolution? How do

organisms evolve?-Natural selection-peer to peer support for 3rd and

6th periods-Hand out CH 17 and 18 V and C

Tomorrow: -Charles Darwin’s findings-Evidence for evolution-species and populations

What is evolution?

1. The process whereby new species arise from earlier species by accumulated change - "descent with modification."

2. The pattern of change of life-forms over time seen in the tree of life as developed from many observations.

3. The mechanism for how evolution happens is largely explained by natural selection.

4. Happens to populations not individuals

5. Can happen over a long period of time or can happen rapidly depending on external factors that may be promoting specific traits over others

4 mechanisms for how Evolution works!

They are: mutation, migration, genetic drift and natural selection

-genetic variation is another important component and is necessary for genetic drift

and natural selection to take place

1. Mutations: -Change in a DNA

sequence usually because of errors in replication or repair

- other factors such as radiation, specific harmful chemicals (essentially causes DNA to break down)

-They are random (can be useful, harmful or not necessary to the function of the organism)

Example: A mutation could cause parents to have a gene for brown coloration instead of green. This would cause genes for brown coloration to be more frequent than they were before this mutation.

2. Migration or gene flow: -Any movement of genes from one population to another

-Can be very important source of genetic variation, especially if those genes did not previously exist in that population

Example: Some individuals from a population of brown beetles might have joined a population of green beetles. That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it.

3. Genetic Drift:

-In each generation, some individuals may, just by chance, leave behind a few more descendents (and genes, of course!) than other individuals.

-It is an entirely random process, and therefore does not lead to adaptations

Example: Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation — but just by chance.

4. Natural Selection:

-Is due to: genetic variation and adaptations; differential reproduction; and heredity and fitness

-Nature chooses viable traits!

Example: Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous

generation.

Ideas That Shaped Darwin's Thinking

1. Age of the Earth - old; slow processes have and are changing Earth (Hutton-1780s & Lyell-1830s)

Darwin - If Earth changes over time, canlife?

2. Theory of Inheritance of Acquired Characteristics - individual drive toward perfection; organisms can pass on to offspring changes they make to their bodies during their lifetime

(Jean Baptiste Lamarck) First naturalist to hypothesize that species are not fixed.

3. Forces work against human population growth - populations can grow faster than resources to support them; leads to disease, famine, etc. (Malthus - 1798)

Darwin - this applies even more to nonhumanspecies; provides mechanism to explain how

evolution works.

4. Artificial Selection (plant & animal breeders)-nature provides variation; humans select those

they find useful Darwin - nature provides the raw material for

evolution; nature selects those that will succeed

Darwin and Wallace’s Theory of Evolution by Natural Selection

There are three main mechanisms that influence the evolution of a species by natural selection:

1. differential reproduction; 2. variation and adaptation; 3. heredity and fitness.

EW: How can a species evolve?

Tuesday, May 13th, 2014

LT: I will be able to explain the mechanisms of natural selection.

Agenda:-Natural selection-Population-Darwin’s findings

Tomorrow:-more evidence of

evolution-phylogenies

Peer to peer support!

• Find someone else in the class that you are partnering up with for this unit.

• During some class time and out of class they will help support you with your goals!

• Get out a sheet of paper.

• Discuss two goals that you both have for this unit in order to complete the portfolio and how you will accomplish those goals, write those down and turn in to me!

1. Differential reproduction (struggle for existence) - more offspring are produced than the environment can support; this leads to competition for resources (food, living space, etc.)

Example:

Green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do.

Example: some beetles are green and some are brown.

2. Variation and Adaptation - Within populations, variations in forms of traits exist. Any heritable characteristic that increases an organism's ability to survive and reproduce is an adaptation.

-Sources of genetic variation include mutations, cross over, random assortment, sexual reproduction and gene flow

Adaptation examples and non-examples

Example: Mimicry of leaves by insects is an adaptation for evading predators. This example is a katydid from Costa Rica.

Example: Echolocation in bats is an adaptation for catching insects.

Non-example: non-functional eyes (vestigial structures) of fish that live in caves

3. Heredity and Fitness- Well adapted individuals are more successful at reproducing and, therefore, pass their adaptive traits on to their offspring, increasing the trait in the population.

Example: The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

More about Fitness

What is fitness? Biologists use the word fitness to describe how good a particular genotype is at leaving offspring in the next generation relative to how good other genotypes are at it.

-The fittest individual is not necessarily the strongest, fastest, or biggest. A genotype's fitness includes its ability to survive, find a mate, produce offspring — and ultimately leave its genes in the next generation.

Example: If brown beetles consistently leave more offspring than green beetles because of their color, you'd say that the brown beetles had a higher fitness.

Recap of Natural Selection:

-Natural selection is not a random process, nature chooses

-Natural selection is not leading to perfection and traits are only adaptive while environmental conditions are adequate for the survival and reproduction of offspring

What is a species?

A species is often defined as a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions.

Speciation

Speciation is a lineage-splitting event that produces two or more separate species.

How can speciation happen?

Geographic isolation (ex.rivers, mountains, streams, islands)

Reproductive isolation (reduction of gene flow)

What are some barriers to gene flow?

Different reproductive timetables

The evolution of different mating location, mating time, or mating rituals

Behavior isolation

Temporal isolation (Different reproductive time tables)

What is a population?

Defining populations-It is a group of organisms that interbreed with each other — that is, they all share a gene pool.

-So For our species of beetle, that might be a group of individuals that all live on a particular mountaintop and are potential mates for one another.

Looking at Darwin’s finches, an example of speciation!

What Darwin hypothesized…

There was a small group of finches in Ecuador.• A small group makes its way to the Galapagos

Islands, possibly blown in a storm or on a land raft.

• The finches can’t get back to the mainland – they don’t like open water.

• Darwin found 14 different species of finches, none identical to the ones on the mainland.

Uniqueness of the finches Darwin found

Warbler finch

Woodpecker finch

Small insectivorous

tree finchLarge

insectivorous

tree finch

Vegetariantree finch

Cactus finch

Sharp-beaked finch

Small groundfinch

Mediumground finch

Large groundfinch

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finch

esGrou

nd fi

nch

es

1. Had different size beaks, this was an adaptation to the food sources on the islands

2. Many were geographically distant from each other, water separated them; habitats were different

3. Different food on different islands

EW: Look at this image. Which candy bars are more closely

related?

Wednesday, May 14th, 2014

LT: I will be able to explain the relationship between cladograms and biological evolution.

Agenda:

-Evidence for evolution

-Phylogenies or Cladogram “Family Tree”

-What did T Rex taste like?

Tomorrow:

-Natural Selection bean lab!

Cladograms

Think about these questions while watching short video:

1. What are cladograms?

2. What relationships do they show?

3. How do they help show evidence for evolution?

Bozeman science cladograms: https://www.youtube.com/watch?v=ouZ9zEkxGWg

Go to this website

http://www.ucmp.berkeley.edu/education/explorations/tours/Trex/index.html

1. Click on the student version

2. Follow along and answer questions on the worksheet

Sexual Selection Artificial Selection