Natural Selection Survival of the Fittest

Natural Selection Review Questions

1. What traits were favored by the female cricket?

2. When it came to the crickets, what does fitness mean?

3. How was nature selecting for the fittest cricket in the cartoon?

Lamark

A. Lammark (early 1800s) believed

organisms evolved through inheritance of

acquired characteristics.

B. However, the inherited characteristics

were modified during your lifetime and

the modifications could be passed onto

your offspring.

• Next, let’s look at 2 examples of

Lammark’s ideas.

Lamark

Example1:Giraffes

stretched out their necks to

reach leaves on tree tops,

and the stretched neck

was inherited.

Example 2: A

father that

pumps iron will

produce a body

builder offspring.

Darwin and Wallace Darwin wrote a

paper on his

thoughts of

evolution in

1842, but fear of

rejection

caused him not

to publish it.

In 1856 Darwin

received a draft of

a paper written by

Wallace with

some of his same

ideas.

So in 1858,

Darwin and

Wallace

submitted

separate

papers to the

Linnaean

Society in

London.

OH! BETTER TURN IN MY PAPER NOW!

• In 1859 Darwin published his book “On

the Origin of Species”

*Darwin’s ideas are the basis of the theory of

evolution. He not only provided evidence

for how organisms change throughout time

but why they change.

CHECKPOINT • Which scientist established that all

species of life have descended over time from common ancestry, and proposed the scientific theory of evolution?

a) Alfred Wallace

b) Jean Baptiste Lamark

c) Charles Darwin

Darwin’s 4 Postulates

1. Individuals in a population differ from

one another. (Diversity or Variation)

Darwin’s 4 Postulates

2. Some differences are

due to characteristics

that are passed down

from parent to child.

(Inherited variation)

Darwin’s 4 Postulates

3. More offspring are produced than

can survive, so some will survive and

reproduce and others will not.

Darwin’s 4 Postulates 4. Survival and reproduction depend on

advantageous traits. Those with traits that

give them an advantage will survive and

have more offspring than those that do

not have advantageous traits.

CHECKPOINT Which is more diverse?

A B

Natural Selection

• Natural Selection is also known as descent

with modification because each species

has descended with changes from other

species over time.

Natural Selection • Natural Selection is

also known as “survival of the fittest” meaning that the most fit organism in the environment will survive .

• Fitness refers to an organisms ability to survive and reproduce.

CHECKPOINT

• Will all the lion cubs survive?

No, Darwin’s 3rd postulate

explains that more offspring are

produced than survive.

Natural Selection • Adaptations are inherited

characteristics that give organisms an

advantage in their environments.

• Over time adaptations can change.

• Natural Selection explains the

changes in populations over time.

Natural Selection

• Natural selection is a

mechanism of evolution,

meaning it causes

evolution.

• It causes changes in allele

frequencies over time.

• Remember an allele is one

form of a gene. (G or g)

Natural Selection

Remember that natural selection chooses

traits that are best for a particular

environment. Nature does not create

prefect individuals nor does it give organisms what they need.

Giraffe’s long necks are

_______ for eating leaves

up high!

Giraffe’s long necks are _______

for drinking because it causes

them to be vulnerable to

predators.

CLICK HERE TO WORK AN EXAMPLE!

CHECKPOINT

ADAPTATION

GOOD OR BAD?

• Remember that natural

selection selects/works on

individuals.

• For, evolution to occur the

population must change

over time.

• Meaning the individuals must

pass their traits on to the next

generation.

Natural Selection

• Individuals do not change when selected.

• By passing on genes that confer an

advantage, they can cause the population

to change.

• The number of the advantageous alleles

becomes more frequent.

Natural Selection

NATURAL SELECTION NOTE PROCESSING

• Follow along the simulation of natural selection.

• http://www.sciencenetlinks.com/interactives/evolution.html

GREEN BEETLES- GG

ORANGE BEETLES- gg Which alleles are more

frequent? GG or gg

Which alleles are more frequent? GG or gg

Did the Allele frequencies change over time? Y N

How many green beetles?

How many orange beetles?

10 6

Did natural selection cause evolution? Y N

Which genotype would have an advantage in a

changing environment? GG Gg or gg

Artificial vs. Natural Selection

• Artificial selection

is also known as

selective

breeding.

• Example: Humans

pick 2 dogs with

desirable traits

and breed them.

•Natural selection

occurs when nature

picks 2 organisms with

desirable traits and

allows them to

successfully

reproduce.

Natural Selection Experiment

• Anolis Sagrei Lizards were removed from

their home of many trees and released

onto 14 small islands that had few trees.

• Researchers returned 14 years later to

discover that the lizards had evolved

shorter, thinner legs. (No longer adapted

for tree life)

CHECKPOINT

• Artificial or Natural Selection?

Artificial Selection – farmers

cultivated crops by selecting

certain attributes of the wild

mustard.

Patterns of Natural Selection

Directional

Selection

• Selects

extreme value

•Example:

Longer nose of

anteater is

selected for.

Stabilizing Selection

•Favors average value

•Example: Small lizards

can’t defend territory

and large lizards are

easily eaten, so

average size lizards

are selected for.

Disruptive Selection

•Favors both

extremes

•Example: Light

and dark clams

survive better in

light and dark

sand. The yellow

can’t blend.

Humans Impact and Evolution

1. Our liberal use of pesticides has led to resistant pests. So we are having trouble protecting our food supply.

2. Our overmedication has led to resistant “super-germs”. So diseases are becoming more difficult to treat.

3. Our heavy fishing has led to smaller fish that slip through nets. So we not able to extract as much food from the sea.