(Chapters 16-17)

Darwin presented evidence that evolution happens and offered an explanation of how it happens.

• Evolution – the process by which species change over time

Theory – a broad explanation that has been scientifically tested and supported

• Keeps developing and expanding as more evidence is uncovered

Most of Darwin’s theory remains scientifically supported to this day.

Charles Darwin was born

Feb. 12, 1809 – the same

day as Abraham Lincoln.

Darwin wanted to understand the biodiversity on Earth.

• Biodiversity – the variety of living things

Darwin was intrigued that so many plants and animals seemed so well adapted to their environments.

Darwin was also impressed by the many ways that organisms survived and reproduced.

Organisms that lived in similar habitats in different parts of the world were very different.

Species vary globally

• Darwin noticed that different, yet ecologically similar, animal

species inhabited separated, but ecologically similar,

habitats around the globe.

• Darwin visited a wide range of habitats on the continents of

South America, Australia, and Africa and he found different

types of flightless ground-dwelling birds on each continent.

South America – rheas; Africa – ostriches; Australia – emus

Species vary globally

• Rabbits and other animals found in the European grasslands

were missing from the grasslands of South America and

Australia.

• Australia was home to kangaroos and other animals that

aren’t found anywhere else.

After finishing college, Darwin sailed with the crew of the

HMS Beagle from 1831-1836.

As the naturalist on the ship, Darwin collected fossils and

living specimen and made thousands of observations

about the organisms and their environments.

The Galápagos Islands – volcanic islands in the Pacific Ocean

near Ecuador

• Many of the plants and animals were similar but not identical to

those found in South America.

Some of the fossils that

Darwin collected looked

similar to species living

today.

Giant Ground Sloth – Megatherium

Some of the fossils that

Darwin found looked nothing

like any thing he had ever

seen.

Darwin’s questions

• Why had so many species

disappeared?

• How were they related to

living species?

Although the Galapagos Islands are

very close together, they have very

different climates.

The plants and animals of each

island were adapted to that specific

environment.

Tortoises – The shape of tortoise shells changed

depending on the type of food available on the island.

Finches – After collecting many species of this bird, Darwin

noticed the size and shape of the beak were different

depending on the type of food available for the finch to eat.

Marine Iguanas – Reptiles that forage underwater for food

but live on land.

Planet Earth 2 Clip

Darwin realized that

variation exists in every

population of

organisms.

Some plants produce

large fruit than others.

Some cows produce

more/better milk than

others.

Some horses run faster

than others.

Breeders were taking

advantage of the variation

in traits within a species.

Select parents with desired

traits to produce offspring

with those traits.

Darwin called this process

artificial selection because

humans were selecting traits.

(AKA – selective breeding)

• Humans choosing mates for

organisms to produce

desired traits in offspring.

Darwin realized

that humans

were driving the

evolution of

many plant and

animal species.

In Darwin’s time (late 1800’s), most

people believed that each species

was created once and stayed the

same forever.

• So, why do we have fossils of

organisms that are no longer here?

Most people believed that the Earth

and living things did not change.

• What about volcanoes, earthquakes,

floods, etc.?

Jean Baptiste Lamarck’s Hypotheses

(1809)

• Organisms change over time.

• All species are the descendants of the

species that came before them.

• All organisms are trying to be more

complex and more perfect.

• Traits pass to offspring based on use

and disuse (use it or lose it).

• Offspring can inherit acquired traits

(like larger, stronger muscles)

Thomas Malthus (1789)

• Observed that the human population

was increasing faster than the food

supply.

• Noted that it could not continue this

way – humans would eventually die

from disease, war, or famine.

Darwin applied this idea to all

populations.

• Populations produce more offspring

than its environment can support,

therefore, many will die.

Georges Curvier

• Argued that fossils in rock layers showed

differences in species throughout time

and many species from the past differed

from those in the present (which implies

change).

James Hutton (1795) and Charles Lyell

(1830)

• Geological processes (like erosion) work

gradually and constantly.

Darwin concluded that the Earth is old

enough for species to evolve gradually.

Darwin waited to publish his ideas

on evolution because he knew that

these ideas were revolutionary and

would challenge the fundamental

scientific beliefs of the day.

In 1858, Darwin received a letter

from Alfred Wallace, a fellow

scientist that was doing similar

studies in Malaysia.

Alfred Wallace’s essay outlined

Darwin’s idea of evolution by

natural selection.

Darwin published his book, On

the Origin of Species by means

of Natural Selection in 1859.

Darwin’s book explained the

process of evolution and

provided evidence that

evolution has been taking

place for millions of years and

continues to happen today.

If you are a pine tree, a fly, or a squirrel, what is your goal

in life?

As a human, what is your ultimate goal in life?

The ultimate goal of every organism is

to SURVIVE and REPRODUCE

Struggle for

Existence

• Members of a

species compete

regularly to obtain

food, living space,

mates, etc.

• A key factor in the

struggle is how well

suited an organism is

to its environment.

Fitness - the ability of an

organism to survive AND

reproduce

Fitness is the result of

adaptations.

Adaptation – any trait

that increase an

organism’s chance of

survival or reproduction.

Camouflage – an adaptation that allows organisms to

blend with the environment to become less visible to

predators or prey.

Mimicry – an adaptation where one species

resembles another species

• Example – A harmless snake looks that looks like a harmful

snake will be avoided.

Better adapted individuals

survive and reproduce

more offspring (higher

fitness)

Less adapted individuals

have less chance of

survival and reproduction

(lower fitness)

Natural selection

• Only certain individuals in a population will produce offspring

• The selected traits increase in the population causing the entire population to evolve not the individual.

• An individual cannot make itself adapt to the environment: its all in the genes.

Evolution is a gradual process of adaptation.

Descent with Modification

• Each living species has

descended, with changes,

from other species over

time.

Descend – to come from

Kings of Camouflage: Cuttlefish (21:20 - 29:46)

Octopus Camouflage

The Fossil Record – all the traces of organisms that lived

in the past

• Comparing fossils and living organisms reveals a pattern of

gradual change from the past to present.

• The fossil record will never be complete because the

conditions necessary to create fossils are rare.

Biogeography – the study of the locations of organisms

around the world

• Scientists have found the movement of landforms in

Earth’s past help explain patterns in the type and location

of both living and fossil organisms.

http://www.youtube.com/watch?v=WaUk94AdXPA&feature=related

Anatomy – comparing the

body structures of different

species

• Closely related species

will have similar structures.

• Homologous

• Analogous

• Vestigal

Homologous structures

– structures that have

developed from the same

tissues in the embryo

(may not have the same

function)

Homologous structures

result from common

genes

Analogous structures – similarities that evolve in

unrelated groups because of similar lifestyles or habitats

due to convergent evolution.

• Example – Birds, bats, and bugs all have wings that are used

to fly but each evolved separately. The structure of the wings

and the genes that produce them are different.

Vestigial Structures – body

parts that do not seem to play a

role in an organism’s life

functions (evolutionary leftover)

• Example – the human appendix

has no apparent function while

rats and other rodents have an

appendix that aids in digestion

• Example – whales and snakes

have a pelvis and femur

Embryology– comparing

the embryonic

development of

organisms to look for

similar patterns and

features

• Not identical but similar

• The closer the

development pattern –

the closer the

evolutionary relationship

Biochemistry – comparing the

genes of different species

• Can compare DNA sequences

or amino acid sequences

• Similar sequences may imply

relatedness

Compare the sequences.

• Which organisms are more

closely related?Human ACT GAG TCG CCT ACG

Monkey ACT GCG TCG CGT ACG

Cow ACT GGG TCA CGT AGC

Strengths

• Supported by a lot of evidence.

• Logical and testable

• Still stands today

Weaknesses

• Darwin knew very little about

genetics.

Mendel was just starting to count

peas (Mendel’s work was not

published until 1900).