NOTES: CH 16 – Darwin’s

Theory of Evolution by Natural

Selection / Evidence for

Evolution

● change over time: the process by which modernorganisms have descended from ancientorganisms.

DEFINITION OF EVOLUTION:

Portrait of Darwin in 1840 (Darwin 65 years old)

(31 years old)

The Life of Charles Darwin

• Born 1809 (England)

• Completed college after studying to become a doctor but could not stand sight of blood …

• Set sail on 5 year voyage on H.M.S., Beagle in 1831 as the natural historian for expedition.

The Life of Charles Darwin

• Made extensive drawings and notes

on the trip but also collected many

species of plants and animals.

• Began to OBSERVE that animals were well

adapted to their environments,

(wondered why were different animals found in areas that appeared to

be similar in climate? and some survived while others did not?)

• Argentina

• Australia

• Europe

The Life of Charles Darwin

All had grasslands but very different animals

• He collected fossils. – noticed some looked like living organisms

– others looked like nothing he had ever seen

before

• Were these related to the living (present day)

organisms?

• Why did some organisms disappear altogether?

The Life of Charles Darwin

The Life of Charles Darwin

Galapagos Islands

Organisms Darwin Observed on the Galapagos• Land Tortoise = different shaped carapace (shell)

depending what island they inhabited.

• Finches = different shaped beaks depending on environment in which they lived.

• he realized that characteristics of many animals and plants varied noticeably among the different islands of the Galapagos.

• On the journey home he began to pose the question…– Could animals on the different islands once

have been members of the same species?

Those Who Influenced Darwin

Hutton (Geologist)

– Geologic processes operate extremely slowly (take millions of years!)

– therefore, the earth is very old

Lyell (Geologist)

– Scientists must explain past events in terms of processes that they can actually observe

• processes that shaped the Earth millions of years ago continue to shape present day Earth

• this explained how geological features can be built or torn down over long periods of time.

Darwin wondered…

• If the earth could change over time, could life change as well?

• Also: it must have taken many, many years for life to change the way Darwin had in mind– This would only be possible if the earth was very

old…

Those Who Influenced Darwin

Malthus (Economist)

• proposed that war, famine, disease,

limits the growth of human populations

• if populations continue to grow

unchecked, they will run out of

resources (food/shelter)

Variation &

Adaptation

2 IMPORTANT CONCEPTS TO HELP US

UNDERSTAND THE PROCESS OF

EVOLUTION:

VARIATION:

differences

between

individuals in a

population

ADAPTATION: inherited

characteristic that increases an

organism's chances of survival

Give me an example, PLEASE!!

EXAMPLES OF ADAPTATIONS!

What are some

adaptations this

polar bear has?

How do they

help polar

bear’s survive?

How are the adaptations of this bear different than those

of the polar bear?

What are some adaptations of a

cactus?

What about this desert plant?

What helps this kelp crab

survive? (It lives on the kelp

in the ocean.)

What the

heck are

these?

EVIDENCE FOR EVOLUTION

1) Fossils:

● evidence of once-living things (shells, casts,

bones, teeth, imprints)

● show a succession of forms through a vast span of

time

● progressive changes based on the order they were

buried in sedimentary rock

few fossils / species many fossils/ species

simple organisms complex organisms

EVIDENCE FOR EVOLUTION

2) Biogeography and age of the earth:

● distribution of plants & animals

13 species of finches on the 13

Galapagos Islands

57 species of kangaroos…

all in Australia!

2) Biogeography and age of the earth:

● Radioactive dating tells us the earth is

about 4.6 billion years old

● Rate of motion of tectonic plates

3) Adaptations: Evidence for Evolution

● MIMICRY: one species resembles another

● CAMOUFLAGE: enables species to blend with their surroundings

● PHYSIOLOGICAL: ability to resist disease or drought

4) “Artificial Selection”

4) Applied Genetics ("artificial selection"):

● Darwin noticed that farmers “selected” the best crops, animals – he wondered if there could be a “selective” force in nature

● today we see DDT-resistant insects; antibiotic-resistant bacteria

5) Anatomical Structures:

Evidence for Evolution

5) Homologous and Vestigial Structures

5) Homologous Structures =

shared common anatomical or biochemical traits

ex: " forearm bones”

• structures that develop from the same clumps of cells

– later develop into structures that have different forms and functions

• arms, flippers, & wings look very similar at the beginning of development, but differ as the animal matures

– The function differs as well!

5) Vestigial Structures:

structures that no longer serve a purpose in an

organism

ex: wisdom teeth, tailbone, appendix, nictitating

membrane, some pythons & boa constrictors have tiny

leftover leg bones (and whales!)

koala's have a large functioning appendix (eat

primarily plant materials)

6) Embryological Development

• Similarities of vertebrate organisms in early

stages of development

• All animal development begins in the same way

(from the same ball of cells)

– BUT recognizable features for that species

develop as the organism grows

•

7) Cellular and Molecular Evidence:

Cellular Evidence

• All organisms are made of cells

– consist of membranes filled with water containing

genetic material, proteins, lipids, carbohydrates,

salts and other substances

7) Cellular and Molecular Evidence

Molecular Evidence

• the DNA code links all life on Earth to a common ancestor– DNA and RNA = simple four-base code that

provides the recipe for all living things

• Transfer genetic material from the cell of one living thing to the cell of another– the recipient would follow the new instructions as if

they were its own• EX: Roundworms share 25% of their genes with humans.

Protein Sequence Similarities!

Review—major evidence for evolution

• Fossil record

• Biogeography and age of the earth

(using radioactive dating)

• Adaptations

• Artificial Selection

• Homologous structures and vestigial organs

• Embryology

• Cellular and Molecular Evidence

EVOLUTION:

DARWIN vs. LAMARCK

LAMARCK’s explanation on evolution

ASSUMPTION #1

CRITICISM OF

THIS

ASSUMPTION

Law of Use and Disuse:

an organism can change

certain body parts during

its lifetime and pass

these changes on.

Implies that an organism

can sense its needs and

change to meet them.

LAMARCK continued…

ASSUMPTION #2

CRITICISM OF

THIS

ASSUMPTION

Inheritance of Acquired

Characteristics: acquired

traits can be passed on to

offspring over time the

population changes.

Suggests that changes in

body cells can be

inherited / passed down.

2 factors that helped DARWIN

formulate his explanation

1) Overproduction

of offspring

occurs in nature;

competition for

food, space,

mates

2) Artificial selection

(selective

breeding) -

Darwin wondered

if a similar force

existed in nature.

Charles Darwin’s Explanation on Evolution

(six major ideas of Darwin)

Overproduction

occurs in nature

Variation occurs in

all populations

Not all organisms

can survive

Variations are

inherited

Populations as a

whole become FIT

= evolved!

Organisms with

favorable variations

survive and

reproduce

LAMARCK:

Individuals

can change

DARWIN:

Evolution

acts on

populations

DARWIN’S THEORY OF

NATURAL SELECTION

1.

ORGANISMS

HAVE MORE

OFFSPRING

THAN CAN

SURVIVE

AND…

…a herd of giraffes would produce hundreds of descendents over several generations.

2. RANDOM, HERITABLE VARIATION EXISTS AMONG THESE ORGANISMS (EX. MUTATIONS), SO…

…by genetic “chance”, some giraffes were born with longer necks.

3. BECAUSE

THERE IS A

STRUGGLE FOR

EXISTENCE

(COMPETITION),

THEN……giraffes were

competing for

food source

(vegetation).

4. THE

ORGANISMS WITH

FAVORABLE

VARIATIONS (THE

“FITTEST”)

SURVIVE AND…

…a long neck

enabled giraffes to

reach an

“untapped” food

source…tree tops!

(short-necked

giraffes ran out of

food and starved)

5. GENES FOR

FAVORABLE

FEATURES ARE

PASSED TO

OFFSPRING

THROUGH

REPRODUCTION,

AND THEREFORE,

THE POPULATION

EVOLVES!!!

The giraffes with

longer necks survive

and pass their genes

(for longer necks) on

to their offspring…the

process continues,

and whole population

EVOLVES.

AND, if populations are

geographically isolated,

changes will accumulate to

the point of reproductive

isolation

( NEW SPECIES!!)

EVOLUTIONARY CONCEPTS• Mutations, genetic recombination, crossing

over, etc. are “accidents” in the genes of

organisms. They do not appear according to

any purpose; they just happen.

• Mutations cause a large amount of variation

among organisms in a population.

• There is room on Earth for only a fraction of

organisms that are born or hatched. The

individuals which happen to have the

mutations giving them the best adaptations to

the environment will be the ones that survive.

EVOLUTIONARY CONCEPTS• The survivors will have their own offspring.

The offspring will be subject to their own

random mutations. Again, only the most

advantageous mutations will result in the

survival of the next generation of offspring,

and hence be “passed down” to the next

generation.

• Countless generations of mutations and

natural selection result in organisms that

have very different structures.