Charles Darwin• Proposed a way how

evolution works– How did creatures

change over time?– by natural selection

• Collected a lot of evidence to support his ideas – 1809-1882– British naturalist

Charles Darwin

• English naturalist• 1831- Began 5 year voyage on HMS Beagle – Traveled to various places in South America and

to the Galapagos Islands– Detailed his observations, took specimens– Concluded that all living things are related• VERY CONTROVERSIAL

Galapagos Turtles

1859- The Origin of Species

• Other naturalists were developing the same theory that Darwin did.

• Even though he was afraid of the Church’s reaction to his book he wanted to get credit for his work.

What did Darwin’s Travels reveal

• The diversity of living species was far greater than anyone had previously known!!

• These observations led him to develop the theory of evolution by natural selection!!

2006-2007

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finc

hes Ground finches

Darwin & Evolution by Natural Selection

Robert Fitzroy

Voyage of the HMS Beagle• Invited to travel around the world– 1831-1836 (22 years old!)– makes many observations of nature

• main mission of the Beagle was to chart South American coastline

Voyage of the HMS Beagle• Stopped in Galapagos Islands– 500 miles off coast of Ecuador

GalapagosRecently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland.

800 km west of Ecuador

Many of Darwin’s observations made him wonder… Why?

Darwin asked:

Why were these creatures found only on the Galapagos Islands?

Darwin found…many unique species

present day Armadillos

Darwin found:

Evidence that creatures have changed over time

ancient Armadillo

Darwin asked:

Why should extinct armadillos & modern armadillos be found on same continent?

Darwin found…clues in the fossils

Darwin found:Different shells on tortoises on different islands

Darwin asked:

Is there a relationship between the environment & what an animal looks like?

Finch? Sparrow?

Woodpecker? Warbler?

Darwin found… birds

Finch? Sparrow?

Woodpecker? Warbler?

Darwin found:Many different birds on the Galapagos Islands.

He thought he found very different kinds…

Darwin was amazed to find out: All 14 species of birds were finches…

Finch? Sparrow?

Woodpecker? Warbler?

Finch? Sparrow?

Woodpecker? Warbler?

But Darwin found… a lot of finches

Large ground finch

Small ground finch

Warbler finch Tree finch

But there is only one species of finch on the mainland! Darwin asked:

If the Galapagos finches came from the mainland, why are they so different now?

Finch? Sparrow?

Woodpecker? Warbler?

The finches cinched it!

Large ground finch

Small ground finch

Warbler finch Tree finch

Big seed eater Small seed eater

Insect eater Leaf & bud eater

Darwin said:

Ahaaaa! A flock of South American finches were stranded on the Galapagos…

Darwin found: The differences between species of finches were associated with the different food they ate.

different beaks are inherited variations

serve as adaptationsthat help birds compete for food

these birds survive & reproduce

pass on the genes for those more fit beaks

over time nature selected for different species with different beaks

Relationship between species (beaks) & food

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

Warbler finch

Woodpecker finch

Small insectivorous

tree finchLarge

insectivoroustree finch

Vegetariantree finch

Cactus finch

Sharp-beaked finch

Small groundfinch

Mediumground finch

Large groundfinch

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finc

hes Ground finches

variation natural selection for best survival & reproduction

From 1 species to 14 species…

Lamarck - Theory of acquired traits

• Organisms develop traits during their lifetime and pass on those traits to their offspring

Malthus

• Reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone

• 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• Darwin– 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’s Postulates

• There is variation among individuals

• Like begets like (traits are inherited)

Postulates cont’d

• Some individuals are most successful at surviving and reproducing than others

• Survival and reproductive success are not random – some characteristics enhance probability of success

Upshot of Darwin’s Postulates

• Those characteristics more common in next generations

=CHANGE

Artificial Selection • nature provides variation, humans select

variations that are useful. • Example - a farmer breeds only his best

livestock

Natural Selection

• The traits that help an organism survive in a particular environment are “selected” in natural selection.

• “Survival of the fittest”

Peppered Moth

Natural Selection and Species Fitness

• Overtime, natural selection results in changes in the inherited characteristics of a population.

• These changes increase a species fitness (survival rate)

Evidence for Evolution

• Homologous Structures

• Embryology

• Fossil Record

Homologous Structures

Embryology

Fossil Record