The Theory of Evolution

In science, theories are statements or models that have been tested and confirmed many times.

Theories have some important properties:

•They explain a wide variety of data and observations

•They can be used to make predictions

•They are not absolute

•They serve as a model of understanding the world and can be changed as the world view changes

The Theory of Evolution is considered a Unifying Theory of Biology, because it answers many of these questions and offers an explanation for the data.

How does evolution explain the origin and development of

species?

The Beginning of the StoryThe Beginning of the Story

Evolution begins with variation.

NO VARIATION = NO EVOLUTION

What causes variation?

What causes variation?

1. List 5 types of variation.

2. List 3 things that can cause variation in an organism?

3. Write them on your clear board.

4. Transfer them into your notes.

In the real world, how do mutations come about?

1. Internal1. Replication errors

2. High energy molecules generated within the organism – free radicals.

2. External1. Chemicals, i.e. mutagens

2. Radiation, e.g. UV, cosmic rays

See video.

Mutations may:

A. Have positive effects

B. Have negative effects

C. Have no effect

D. All of the above

All of the following can be causes of mutation except:

A. Mutagenic chemicals

B. An organism’s need to be successful

C. Radiation from the sun

D. Free radicals

Whether a mutation is positive or negative depends the location of the

mutation in the genome:

True

False

Whether a mutation is positive or negative depends on the environment

of the organism.

True

False

Which of the following statements is false:

A. Mutations occur all the time.

B. Everyone has mutations.

C. Mutations always lead to a decrease in success of the organism.

D. Mutations can be caused by a variety of factors.

Tracking Mutations• Mutations occurring in the genes of the

gametes are inherited by offspring.

• These mutations may show up through thousands of generations as the same chromosome is transmitted from parent to child.

• Understanding these mutations can tell us a lot about the ancestry of organisms including humans.

What specific name do we have for inherited mutations?

A. Chromosomes

B. Markers

C. Genes

D. Gametes

What genetic material does a man always inherit?

A) His mother’s paternal chromosomes

B) His father’s paternal chromosomes

C) His father’s Y chromosome

D) All of his fathers chromosomes

What is the name of the people the scientist is investigating?

A. Koi San

B. Africans

C. Kenyans

D. Aborigines

Why is Dr. Wells so interested in these bushmen?

A. He thinks they may have some special genes that can be used in medicine.

B. He thinks they may be the group most closely related to our ancestors who left Africa.

C. He thinks they may have invented the bow and arrow.

D. He thinks they may have invented spoken language.

Meiosis and fertilization allow for great diversity in sexual species compared to asexual species.

In evolutionary terms, sex is more important than life itself. Sex fuels evolutionary change by adding variation to the gene pool. The powerful urge to pass our genes on to the next generation has likely changed the face of human culture in ways we're only beginning to understand.

Why Sex?Why Sex?

Traits can be positive, negative or neutral in a given environment.The alleles coding for negative traits are likely to be reduced in the presence of alleles for more favorable ones.

Team Question

The types of variation we have been discussing can have an impact on the success of an organism.

Biologically speaking, what is “success?”

Essential requirements for EvolutionVariation: All life forms vary genetically within a population. It is this genetic variation upon which selection works.

Inheritance: Genetic traits are inherited from parents and are passed on to offspring.

Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation.

Time: Evolution takes time. Evolution can happen in a few generations, but major change, such as speciation, often takes long periods of time.

CHARLES DARWIN – 1809-1882

• English• Traveled around the world on

the Beagle – famous in the Galapagos islands

• Observed many species and fossils

• Why did some species survive while others became extinct?

• Natural selection

Voyage of the HMS Beagle

Stopped in Galapagos Islands 500 miles off coast of Ecuador

I have called this principle, by which

each slight variation, if useful, is preserved, by the term Natural

Selection.

  —Charles Darwin from "The Origin of Species"

NATURAL SELECTIONNATURAL SELECTION

Organisms with traits well suited to an environment are more likely to survive and produce more offspring than organisms without these favorable traits

Types of selection

Selection causes some traits to survive and spread, while others are lost. A selection pressure determines which traits are successful.

Starting population has a normal distribution

of traits.

mode

There are three types of selection: disruptive, stabilizing and directional.

Selection can be represented using graphs showing the distribution of individuals with a particular trait.

trait

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mode mode

Types of selection

stabilizingdisruptive directional

Selection can cause the mode and/or distribution to change.

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trait

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trait trait

Selection pressure toward

the extremes creates two

modal values.

Selection pressure toward the center

increases the number of

individuals at the modal value.

Selection pressure toward

one extreme moves the mode in this direction.

mode

LaMarck– evolution by acquired traits

• creatures developed traits during their lifetime

• give those traits to their offspring– example

• in reaching higher leaves giraffes stretch their necks & give the acquired longer neck to offspring

– not accepted as valid

Earlier ideas on Evolution

Darwin’s view of Evolution– giraffes that already

have long necks survive better

– leave more offspring who inherit their long necks• variation• selection &

survival• reproduction &

inheritance of more fit traits

Darwin made extensive use ofspecimens and fossil evidence toexplain his theory of evolution,but because DNA andgenes had not yet beendiscovered, he was unableto explain why traits varied within individuals or how they were inherited.

Could Darwin explain everything?

Victorian scientists found it difficult to test Darwin’stheory. For his theory to work, the Earth needed to be millions of years old, but its age was not known at that time.

In addition, little was known about the process of fossilization or how to explain gaps in the fossil record.

Natural Selection

1. Overproduction

2. Competition

3. Variations

4. Survival of the fit

1. Overproduction

Organisms produce more offspring than the environment can support.

There is not enough food or living space for all the offspring.

2. CompetitionOverproduction leads to a struggle.All the organisms compete for food, water, and

the other necessities of life.Only those organisms that are well suited to their

surroundings survive and reproduce.The rest die.

3. Variations

Organisms of the same species are very similar.

But they do have individual differences among traits, or variations.

These differences are important in the ”struggle for survival.”

For example, extra speed can mean the difference between life and death. A fast wildebeest may escape an attacking lion. A slower neighbor may become the lion’s next meal.

4. Survival Of The FitOrganisms with traits that

make them well adapted, or suited to the environment, survive and reproduce.

Darwin used the term natural selection to describe the survival of organisms with favorable traits.

They, in turn, pass their favorable traits to their offspring.

The offspring are then more likely to survive.

As the process of natural selection goes on over many generations, species change.

Galápagos finches

Darwin thought all the finches could have evolved from one type of finch that came from the mainland.

Some finches had strong and claw-like beaks, suitable for crushing seeds.

Other finches had thin and delicate beaks, suitable for picking insects from holes in the ground.

In the Galápagos, Darwin noticed that different islands had different types of finches, with different types of beak.

Natural variation meant that some finches had slightly different beaks. These finches would have been able to eat different types of food and avoid competition. They wouldtherefore have survived and passed on their genes.

Darwin’s finches

Darwin’s conclusions – variations in beaks

• differences in beaks in the original flock

• adaptations to foods available on islands

– natural selection for most fit• over many generations, the finches were selected for

specific beaks & behaviors

– offspring inherit successful traits• accumulation of winning traits:

both beaks & behaviors

– separate into different species

Peppered moths rest on tree trunks during the day. Some are light colored and others are dark.

The number of light colored moths is increasing.

Cities are cleaner now. What difference has this made?

Peppered moths

When cities were very polluted in the 19th century the number of previously rare dark colored moths increased, as they were better camouflaged against predators on soot-stained trees.

These changes can result in the appearance of a new species.

Evolution by natural selection occurs.