E. Coleman 2010

The Origin of Species

“Evolution” means change over time.

The “Theory of Evolution” says:

– Living things on Earth have changed over time.

– Many species that once existed are now extinct. – Many species alive today were not here when life on Earth first formed.

First thought of by the ancient Greeks (in 600 BC ) but they did not try to explain HOW it happened.

First scientific attempt to explain how evolution happened came 2400 years later! In 1802 Jean LAMARCK Jean LAMARCK proposed model:proposed model:

Evolution by Acquired CharacteristicsEvolution by Acquired Characteristics 1. More individuals are born than the

environment can support - there is a struggle to survive.

2. Some individuals respond by developing traits that give them a better chance to survive.

3. When these individuals reproduce their offspring inherit their newly acquired, improved traits and develop them even further.

4. Eventually ALL members of the species have the favorable trait. Jean Baptiste Lamarck

1744-1829

Lamarck’s explanation of how the giraffe got its long neck:Lamarck’s explanation of how the giraffe got its long neck:

1. ALL early giraffes had the same (short ) necks.

1 2 3

2. As giraffe population increased there wasn’t enough foodwithin reach for all so some began stretching their necks to reach food higher in the trees. – The more they stretched, the longer their necks grew.

3. When they reproduced they passed their longer necks on to their offspring who stretched their necks even more. – Eventually all giraffes had long necks.

Lamarck’s model was quickly discarded. Scientists tried but could not find evidence to support his main ideas.1. All members of a species are NOT alike as

Lamarck said. Great variation normally and naturally exists within a species.

3. Organisms can change and improve some things during their lifetimes (lifting weights to increase strength etc.) but these traits CANNOT be

passed to offspring. If this man wants his future children to have small noses will it help to get a nose job??

2. Organisms cannot change most of their basic physical traits at will, even if survival depends on It. They cannot “adapt” because they need to. For example giraffes cannot make their necks grow longer by stretching them!

Is there anything he could do that might help?

In 1831, Charles Darwin (failed medical student, failed divinity student, avid beetle

collector) began a 5 year journey on a small ship, the H.M.S. Beagle.

Charles Darwin1809-1882

90’ long

75 people

5 years

Aroundthe world!

Purpose: survey coast of South AmericaDarwin’s job: observe geology & biology of the area.

– Did NOT set out to develop a model, but couldn’t ignore what he saw. Hiscuriosity drove him to try to explain what he had observed.

– Kept meticulous records of observations. His observations from the

Galapagos IslandsGalapagos Islands led to his model of how evolution occurred.

Galapagos IslandsGalapagos Islands are 600 miles off west coast of Ecuador (South America).

Volcanic -

first rose above the

ocean surface less than 15 million years ago.

Why is this special?Why is this special?1) Life has been there a relatively short time (compared to billions of years on the mainland!). 2) It developed in isolation from life on the mainland.

High lush island

Low, desert island

Darwin was surprised to find species that clearly were closely related but that had distinct differences on different islands.

He also discovered many species that were found nowhere else on Earth, including the world’s only swimming lizard.

It was hard for him to accept the prevailing beliefthat all of these species had been separately created.

After returning to England Darwin spent 25 more years gathering evidence. He also studied species selectively bredby humans for desired traits - in particular, fancy pigeons andthe many breeds of dogs created by 10,000 years of selectivebreeding.

In 1859 Darwin published his model:

At the time he waswidely criticized

and ridiculed.

On THE ORIGIN OF SPECIESOn THE ORIGIN OF SPECIES

by Means of Natural Selectionby Means of Natural Selection

Darwin’s explanation of how evolution occurred:

2. Within every species there is naturally variation.

1. More individuals areborn in a species than the environment cansupport. There is a struggle to survive.

3. Variations of some give them anadvantage over others in the struggle tosurvive.

4. More of these individuals will surviveand reproduce than will those with lessfavorable traits.

6. More individuals with favorable traits reproduce, so the # of individuals with favorable traits increases in each generation.The # with less favorable traits decreases.

7. Eventually the favorable trait becomes the most common form and over many generations (and usually millions of years) such differences accumulate until a new species results.

5. Many traits are passedfrom parents to offspring.

Does it sound familiar???

Darwin called his modelDarwin called his model

““Natural Selection”Natural Selection”

1. Ancestral giraffes had necks of various lengths.

1 2 3

How Darwin explained the giraffe’s How Darwin explained the giraffe’s long neck:long neck:

2. When food became scarce, longer-necked individuals could reach more food sources so they survived in greater numbers than those with shorter necks, many of whom starved and died.

– more long necks survived, so more reproduced and passed the long-necked trait to their offspring.– each generation had more long and fewer short necksthan the one before.

3. Eventually after many generations and millions of years ALL giraffes had long necks.

Unlike Lamarck, the ideas in Darwin’s model were found to be consistent with observations and scientific evidence. In fact they continue to be supported by all evidence gathered in the 150 years since they were first published. This includes hundreds of thousands of experiments, studies, archeological

finds, and facts.

Scientists are so confident that Darwin’s model is correct that it is now called

a THEORY - The Theory of Evolution by Natural Selection.

Warm Up

• If you get an infection, and are given an antibiotic, and you get better. Then you get a second infection, and you are given the same medicine, but you don’t get better. What happened? Use natural selection to describe the process.

Meaning of THEORYTHEORY in science: a comprehensive model that takes into account all known

evidence (facts, observations as well as scientific laws) and

explains a wide range of natural phenomena.

• Theories are the models scientists are MOST certain about.• Must be supported by MANY different lines of evidence.• Must be changed if new evidence is discovered.• Must provide a reliable basis for scientists to make and test

predictions.

Scientific LawsScientific Laws All FactsAll Facts All ObservationsAll Observations

JustJust 3 3 theories organize all knowledge in Biology:theories organize all knowledge in Biology:

CELLTHEORYCELLTHEORY - all living things are made of cells. (1838)

CENTRAL DOGMA -CENTRAL DOGMA -

explains what DNA and RNA do and how they do it. (1958)

THEORY OF EVOLUTION byTHEORY OF EVOLUTION byNATURAL SELECTION NATURAL SELECTION (1859)(1859)

MANY LINES OF EVIDENCE SUPPORT DARWIN’S THEORY:1. FOSSILS

Even in Darwin’s day, change in life forms over time was apparent in fossils found in different layers of rock. This type of dating is referred to

as relative dating.

NEWER

OLDER

Today isotope dating: called absolute dating and DNAanalysis allow precise determination of fossil age. Most results agree with earlier studies based on layering alone.

Histories of many Histories of many species have been species have been reconstructed reconstructed using layering and using layering and other other

forms of dating.forms of dating.

Histories of many Histories of many species have been species have been reconstructed reconstructed using layering and using layering and other other

forms of dating.forms of dating.

2)Another evidence: Embryology

SIMILARITY OF EMBRYOS

LEMUR PIG HUMAN

Which is a human? A lemur? A pig?

3. MOLECULAR EVIDENCE3. MOLECULAR EVIDENCE

All living things have the same make-up at theAll living things have the same make-up at the molecular level.molecular level.

4. ANATOMICAL EVIDENCE4. ANATOMICAL EVIDENCEAnatomical similarities reveal common ancestry.Anatomical similarities reveal common ancestry.

Example:Example: All vertebrate forelimbs contain the same set of bones (they’reAll vertebrate forelimbs contain the same set of bones (they’re““homologous”).homologous”).

5. DNA EVIDENCE

• Every organism’s DNA is unique.

• But most of our DNA is the same as all living things.

• The more closely related organisms are, the more of their DNA that is the same.

96% of Chimp and Human DNA is identical !

PREDICTIONS THAT FOLLOW FROM DARWIN’S THEORY OF NATURAL SELECTION:

1. There should be fewer and fewer species as we go back toward the beginning of life 3.5 billion years ago.

2. Earlier organisms should be simpler than modern ones. As organisms evolved they became more complex.

3. We should see evidence of life forms that are no longer found on Earth.

4. There should be differences between these organisms and modern organisms.

5. All organisms should have some characteristics in common.

6. Some organisms will be “in-between”, i.e. have traits that make them hard to classify.

ALL of these predictions have been tested and supported.

The Theory of Evolution by Natural Theory of Evolution by Natural SelectionSelection as proposed by Charles Darwin (and (and Ms. Ms.

Lopez’s fabulous Biology studentsLopez’s fabulous Biology students ! ) ! ) is supported by all credible scientific evidence collected before and since.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

CHECK YOUR UNDERSTANDING:CHECK YOUR UNDERSTANDING:

1. Would you expect individual organisms to “evolve” in their lifetime?

2. What does evolve over time?3. What “force” shapes the characteristics of species - in

other words, what “selects” traits?

4. What might cause evolution to“speed up” - that is, cause species to change more rapidly?

5. What was the original cause of variation within species?

NO!SPECIES EVOLVE!

THE ENVIRONMENT

DRASTIC CHANGE IN ENVIRONMENT

MUTATION