2006-2007

Insect eaters

Bud eater

Seed eaters

Cactuseater

Warbler

finch

Tree

finch

es

Ground finches

Darwin & Evolution by

Natural Selection

Incorrect Theories of Evolution: Lamarck

• Lamarck proposed an incorrect mechanism for how organisms evolve.– Believed organisms could pass on aquired traits

to offspring– Simple life forms continually came into

existence from dead matter – Continually become more complex– More "perfect" -- as they transformed

into new species. • He correctly pointed out that change in

species is linked to an organism’s environment.

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– -Wrote the Origin of

Species

Robert FitzroyRobert 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

Darwin’s Observations

• Animals on the coast of S. America:

– Resembled those on the nearby islands

– Evolved differences Or

– Descended w/ modification after separating from a common ancestor.

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

Evidence that creatures that creatures have changed over timehave changed over time

ancient Armadillo

Darwin asked:Darwin asked:

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

Darwin found…clues in the fossils

present day Sloth

Darwin found… more fossils

Darwin asked:Darwin asked:

Why should extinct Why should extinct sloths & modern sloths & modern sloths be found on sloths be found on the same continent?the same continent?

(extinct) Giant ground sloth

Darwin found:Darwin found:

Evidence that creatures that creatures have changed over timehave changed over time

Darwin found:Different shells on tortoises on different islands

Darwin asked:Darwin asked:

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

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

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

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:Darwin asked:

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

QuickTime™ and aPhoto - JPEG decompressor

are needed to see this picture.

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:Darwin said:

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

finch

esG

round finches

variationnatural selection for best survival & reproduction

From 1 species to 14 species…

Growth of Populations

• Darwin was influenced by Thomas Malthus• He wrote: Populations grow as much as the environment allows.

Evolution by Natural Selection

• The process of: “Survival of the FittestSurvival of the Fittest” • Organisms that adapt

to their environment survive while those that do not adapt disappear

• N.S. leads to adaptationsadaptations in a population.

ADAPTATIONS LEAD TO FITNESS

Living things that are well adapted to their environment survive and reproduce. Those that are not well adapted don’t survive and reproduce.

An adaptation is any characteristic that increases fitness, which is defined as the ability to survive and reproduce.

YOU CANNOT AQUIRE AN ADAPTATION, MUST BE AN INHERITED TRAIT.

Label Paper:1. Genetic Variation

a.

b.

2. Overproduction of Offspring a.

b.

3. Struggle for Existence a.

b.

4. Differential Survival & Reproduction a.

b.

Natural Selection Video

http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html

6 min 39 sec

SUMMARY: Individuals best suited to their environment survive and reproduce most successfully. The characteristic that make them best suited to their environment are passed on to offspring.

Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring.

Species change over time. This is natural selection.

Over long periods of time, natural selection causes changes in the characteristics of a species, such as in shape and form. New species arise, and other species disappear.

African wilddog

•These five canine species evolved from a common ancestor through natural selection

FoxThousands tomillions of yearsof natural selection Wolf

Ancestral canine

Coyote

Jackal Fox

Species alive today have descended with modifications form species that lived in the past.

Darwin’s Ideas Updated

1) Change Within Populations• N.S. causes the frequency of certain alleles in a population

to change over time.

2) Species Formation • Under certain conditions, change within a species due to

reproductive isolation can lead to new species.

3) The Tempo of Evolution • Gradualism is a process of evolution in which speciation

occurs gradually • Punctuated Equilibrium is a process in which speciation

occurs rapidly between periods of little or no change.

Natural Selection at WorkExamples of Evolution--

1) Factors in Natural Selection • Organisms w/traits helping them survive—

reproduce & pass genes. 2) Evolution of Antibiotic Resistance • Experiments show that evolution through N.S. has

occurred within populations of antibiotic-resistant bacteria– Tuberculosis bacteria

3) Evolution in Darwin’s Finches• Experiments show that evolution through N.S. has

occurred in beak size in Darwin’s Finches.

1) SpeciationSpeciation • Speciation begins as a population adapts to its

environment. 2) Forming Subspecies • Populations of the same species that differ

genetically b/c of adaptations to different living conditions are called: subspeciessubspecies.

• Newly formed subspecies are on the road towards speciation.

3) Maintaining New Species • Reproductive isolation through barriers keeps

species from breeding with one another.

Formation of New Species

Speciation

• Geographic isolationGeographic isolation of populations• Can lead to

• Reproductive isolation of population • Can lead to

• New Species • (unable to breed when together)

Geographic Isolation• Members of

a population may become isolated from one another by geographic boundaries like mountains, rivers or even oceans

Reproductive Isolation

Convergent Evolution

Divergent Evolution(Adaptive Radiation)

Dichotomous Keys• Tool used when new species is found

• Used to categorize different species based on physical characteristics

• ClassificationClassification is a way of separating a large group of closely related organisms into smaller subgroups.

• A Dichotomous Key is a listing of characteristics, such as structure and behavior, organized in such a way that an organism can be identified or classified.