Darwin vs. Lamarck

Lamarck Darwin

Jean-Baptiste LaMarck

• French, Early 1800’s

Theory of Inheritance of

Acquired Characteristics• Two main points…

1. Principle of Use & Disuse: • Most used body structures develop, unused

structures waste away

2. Inheritance of Acquired Characteristics:

• Once the structure is modified, the new trait can be inherited (passed to offspring)

Explain the picture below as if you were LaMarck…

Why we don’t believe him…

•Genetics: Gregor Mendel discovered that traits are passed down through GENES (which aren’t affected by the outside world in that way)

•Experiments: show that changes that occur in an animal’s life are not passed on to its offspring

Charles Darwin“The Father of Evolution”

• 1831- sailed on the HMS Beagle to the Galapagos Islands.

• Studied many species of finches.• Published book in 1845:

• “On the Origin of Species by Natural Selection”

Darwin’s Theory of Evolution

(don’t copy all this it’s on your handout)

“Survival of the Fittest”

“Natural Selection”

Natural Selection

• Process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.

Natural Selection

Four main points…

• 1. More organisms are produced than can survive…leads to COMPETITION OVER RESOURCES

• Ex’s of resources…• Water• Food• Habitat• Mates

2. Individuals within a population vary, and some of these traits are heritable.

3. Some variations are FAVORABLE (increase chances for

survival/ reproduction)• Male vs. Female

Cardinals• Male color attracts

female= reproductive advantage

4. Better adapted individuals survive and reproduce

• These are the individuals that will pass on their genes to the next generation.

• This can change the GENE POOL:• Includes all the genes of every

reproductive member of a population

What The theory of evolution IS NOT!!!• It does NOT occur in INDIVIDUALS…

only populations!• It does NOT happen quickly…the Earth

has a Looooooong history!• It does NOT explain how life came to be

on Earth, just how it evolved after it was here.

• It does NOT have any driving force except the competition for limited resources.

Species…

• A group of organisms that are genetically similar enough to produce healthy, fertile offspring.

Darwin’s Finches…p 558• Illustrate SPECIATION: when a

species breaks into two (or more)• The organisms in the two species can no

longer…• INTERBREED

• What could cause this to happen?• Geographic barriers• Occupy a new niche/habitat• Reproductive Isolation-

Natural selection

What would Darwin say to explain why giraffe’s have such long necks?• See pg. 553•

Types of Natural Selection

• Stabilizing Selection• Occurs when natural selection works

against the 2 extremes of a trait to make the population more uniform.

Stabilizing Selection

Stabilizing Selection

• Birth weight of babies• Babies that are too big or too small might

have less chance of being born healthy.

Natural Selection

• Directional Selection• Selects the extreme of 1 trait.

Directional Selection

• In a population of plants, flowers with the brightest color might be selected for in order to attract the most pollinators.

Natural Selection

• Disruptive Selection• Selects against the mean of the population.

Disruptive Selection• If there are 2 types of seeds to eat for a

population of birds, either of 2 different beak shapes (sharp or blunt) might be selected for, but a beak that’s the average of the 2 shapes might not be particularly good at eating either seed, so it would be selected against.

Evolution- “Change Over Time”• All of the changes that have occurred in living things

since the beginning of life on Earth

History of the Earth

4.5 bya •Earth forms

3.5 bya•1st PROKARYOTES

2.1 bya •1st EUKARYOTES

700 million years ago…

MULTICELLULAR ORGANISMS!

Three important points…

• Evolution occurs over MANY generations

• Evolution occurs within POPULATIONS (NOT individuals)

• Evolution involves genetic changes in a SPECIES• (Members of a species interbreed to

produce healthy, fertile offspring)

The process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common.

1. Evolution2. Natural Selection3. Adaptations4. Genetic

Recombination

Consider, for example, a population of shellfish called limpets. The shell color of these limpets ranges from white, to tan, to dark brown. As adults, limpets live attached to rocks. On light-colored rocks, white-shelled limpets have an advantage because their bird predators cannot easily see them. On dark-colored rocks, dark-colored limpets have the advantage because they are camouflaged. On the other hand, birds easily see tan-colored limpets on either the light or dark backgrounds. These tan-colored limpets will be at a selection disadvantage and will most likely become extinct from the population. This type

of natural selection is known as:

Stabiliz

ing Sele

ction

Directi

onal Sele

ction

Disrup

tive S

electi

on

0% 0%0%

1. Stabilizing Selection2. Directional Selection3. Disruptive Selection

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24

Consider a population of spiders in which the average size is a survival advantage. Predators in the area might easily see and capture spiders that are larger than average. However, small spiders may find it difficult to find food. Therefore, in this environment, average-sized spiders are more likely to survive. This type of natural

selection is known as:

Stabiliz

ing Sele

ction

Directi

onal Sele

ction

Disrup

tive S

electi

on

0% 0%0%

1. Stabilizing Selection2. Directional Selection3. Disruptive Selection

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24

Imagine a population of woodpeckers pecking holes in trees to feed on the insects living under the bark. Suppose that a species of insect that lives deep in tree tissues invades the trees in a woodpecker population’s territory. Only woodpeckers with long beaks could feed on that insect. Therefore, the long-beaked woodpeckers in the population would have a selective advantage over woodpeckers with very short or average-sized beaks. This

type of natural selection is known as:

Stabiliz

ing Sele

ction

Directi

onal Sele

ction

Disrup

tive S

electi

on

0% 0%0%

1. Stabilizing Selection2. Directional Selection3. Disruptive Selection

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24

The smallest unit that can evolve is:

A genome

An indivi

dual

A commun

ity

A populatio

n

0% 0%0%0%

1. A genome2. An individual3. A community4. A population

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21 22 23 24

Genetic Equilibrium• Not all populations are in an active state

of “natural selection”• GENETIC EQUILIBRIUM

• This means that there is no change in the gene pool = no evolution

Genetic Equilibrium

• 1.) Population size is large• 2.) No gene flow in the population

• No new organisms introducing more alleles• 3.) No mutations• 4.) No environmental factors causing

natural selection• No trait is favorable over another

• 5.) Random mating must occur

So what factors exist to make a population evolve?

• It must NOT be in GENETIC EQUILIBRIUM

• Something that knocks the population out of genetic equilibrium is called a

MECHANISM OF EVOLUTION

Mechanisms of Evolution• 1. Natural Selection• 2. Sexual Selection / Non-random mating• 3. Mutation• 4. Gene Flow (Migration) • 5. Genetic Drift- reduces population size

• Bottleneck effect• Founder effect

How does reproduction affect natural selection• Discuss with your partner:

• How would a population that reproduces asexually “evolve”

differently than one that reproduces sexually? WHY?

A note on sexual reproduction…• Sexual reproduction can produce many

different phenotypes• Sexual reproduction does NOT change

relative frequency of alleles in a population

• Think about shuffling a deck of cards• Shuffling cards gives you different hands• It won’t change the number of kings in a

deck