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Biology 3

Origin and Diversity of Life

Dr. Terence Lee

What is Life?

Virus? Ice Crystal?

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What is necessary for Life?

CONDITIONS ON EARTH AT THE TIME LIFE BEGAN

The early atmosphere differed from that of today, and contained large amounts of carbon dioxide, nitrogen, methane, ammonia, hydrogen, and hydrogen sulfide.

Small organic molecules eventually formed, providing the building blocks of life.

In 1953, Stanley Miller and Harold Urey developed a simple four-step experiment that demonstrated how complex organic molecules could have arisen in earth’s early environment.

THE UREY-MILLER EXPERIMENT

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THE UREY-MILLER EXPERIMENT

They created a model of the chemicals present in the "warm little pond" and atmosphere early in earth's history: H2, CH4 (methane), and NH3 (ammonia).

The atmosphere was subjected to sparks, to simulate lightning.

The atmosphere was cooled so that any compounds in it would rain back down into the water.

They examined the water, looking for organic molecules.

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Within a matter of days they discovered many organic molecules (including five different amino acids) in their primordial sea.

Heat

Electrical charge

Cool

RNA World Hypothesis

• The world may have been filled with RNA-based life…

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Why are cell membranes

important?

• Allow for higher concentrations of chemicals inside the cell relative to the outside.

WHAT MAKES A SPECIES?

SPECIES ARE• populations of organisms that interbreed with each other,• or could possibly breed, under natural conditions,• and are reproductively isolated from other such groups.

Reproductive Isolation

• Hybrids are bad.

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Reproductive Isolation

• Two ways to prevent hybrids:

1. Prezygotic isolating mechanisms

2. Postzygotic isolating mechanisms

Conrad Lorenz

• Prezygotic isolating mechanisms

REPRODUCTIVE ISOLATION: KEEPING SPECIES SEPARATE

PREZYGOTIC BARRIERS• Individuals are physically unable to mate with each other.

OR• If individuals are able to mate, the male’s reproductive cell is

unable to fertilize the female’s reproductive cell.

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• Postzygotic isolating mechanisms

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REPRODUCTIVE ISOLATION: KEEPING SPECIES SEPARATE

POSTZYGOTIC BARRIERS• Matings produce hybrid individuals that do not survive long after

fertilization.OR

• If hybrid offspring survive, they are infertile or have reduced fertility.

How do we name species?

• Every species has a two part name.

1. Genus

2. specific epithet (species)

• Example: Homo sapiens (Genus species)

– The first letter of the Genus is always capitalized.

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THE ORGANIZATION OF LIFE

DOMAIN

KINGDOM

PHYLUM

CLASS

ORDER

FAMILY

GENUS

SPECIES

Bacteria Archaea Eukarya

Protists Plants Fungi Animals

Chordata

Mammalia

Artiodactyla

Giraffidae

Giraffa

Giraffa camelopardalis

Memorizing Scientific

Classifications

1. Kingdom

2. Phylum

3. Class

4. Order

5. Family

6. Genus

7. Species

1. Kings

2. Play

3. Chess

4. On

5. Fine

6. Green

7. Squares

THE BIOLOGICAL SPECIES CONCEPTDOESN’T ALWAYS WORK

The biological species concept is remarkably useful when describing most plants and animals, but it doesn’t work for distinguishing all life forms.

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CLASSIFYING ASEXUAL SPECIESAsexual reproduction does not involve interbreeding, so the concept of reproductive isolation is no longer meaningful.

CLASSIFYING FOSSIL SPECIESDifferences in size and shape of fossil bones cannot reveal whether there was reproductive isolation between the individuals from whom the bones came.

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THE BIOLOGICAL SPECIES CONCEPT DOESN’T ALWAYS WORK

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DETERMINING WHEN ONE SPECIES HAS CHANGED INTO ANOTHERThere is rarely a definitive moment marking the transition from one species to another.

CLASSIFYING RING SPECIESTwo non-interbreeding populations may be connected to each other by gene flow through another population, so there is no exact point where one species stops and the other begins.

5 CLASSIFYING HYBRIDIZING SPECIESHybridization—the interbreeding of closely related species— sometimes occurs and produces fertile offspring, suggesting that the borders between the species are not clear cut.

Ring Species

How do new species arise?

• Speciation describes the process of one species splitting into two distinct species in two phases.

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Speciation

• Allopatric Speciation

– Physical barrier divides a population in two.

– Ex. Mountain range, desert, ocean, river, etc…

ALLOPATRIC SPECIATION

Allopatric speciation occurs when a geographic barrier causes one group of individuals in a population to be reproductively isolated from another group.

INITIAL POPULATION1

ALLOPATRIC SPECIATION

REPRODUCTIVE ISOLATIONSuppose a river forms through the squirrels’ habitat, separating the population. Because they cannot cross the river, they are reproductively isolated.

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ALLOPATRIC SPECIATION

REPRODUCTIVE ISOLATIONSuppose a river forms through the squirrels’ habitat, separating the population. Because they cannot cross the river, they are reproductively isolated.

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Harris’s antelope ground squirrel

White-tailed antelope ground squirrel

ALLOPATRIC SPECIATION: GALÁPAGOS ISLAND FINCHES

Large cactus finch Small tree finchWoodpecker finchLarge ground finch Vampire finch

� Due to allopatric speciation, fourteen different species of finches have evolved in the Galápagos Islands. Only one species of finch is found on the nearest mainland.

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Speciation

• Sympatric

speciation

Allopatric Sympatric

SYMPATRIC SPECIATIONSympatric speciation results in the reproductive isolation of populations that coexist in the same area. Two scenarios, common in plants, lead to this method of speciation.

POLYPLOIDY

During cell division, an error occurs in which chromosomes are duplicated but the cell does not divide. This creates a gamete with twice as many sets of chromosomes as a gamete of the parent from which it came.

A gamete with two sets of chromosomes cannot produce offspring by fertilizing a gamete with one set of chromosomes.

A gamete with two sets of chromosomes can, however, produce offspring by fertilizing another gamete with two sets of chromosomes, producing an individual with four sets of chromosomes.

Gamete Gamete

Gamete Gamete

Parent cell

MEIOSIS

FERTILIZATION

New individual

Gametes

The new individual has achieved instant reproductive isolation from the original population and, therefore, is considered a new species.

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SYMPATRIC SPECIATIONSympatric speciation results in the reproductive isolation of populations that coexist in the same area. Two scenarios, common in plants, lead to this method of speciation.

ALLOPOLYPLOIDY

Two plants from different but closely related species interbreed, forming a hybrid.

The hybrid may no longer be able to interbreed with either of the parental species.

The hybrid may, however, be able to propagate itself asexually—as many plants can.

HybridSpecies 1 Species 2

FERTILIZATION

Species 1

The hybrid individual has achieved reproductive isolation from the original parental populations and, therefore, is considered a new species.

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Species 2

ASEXUAL REPRODUCTION

Hybrid

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Micro vs. Macro Evolution

• Micro = slight changes in allele frequencies over one or a few generations

• Macro =

EVOLUTION: MICRO vs. MACRO

Evolution is one thing only: a change in allele frequencies within a population. But over time, these changes can lead to new species and groups of species that vary tremendously.

MACROEVOLUTIONThe accumulated effect of microevolution over a long period of time

MICROEVOLUTIONA slight change in allele frequencies over one or a few generations

Time

Rate of Evolution

• Not constant over time

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Rates of Evolution

• Gradualism

Rates of Evolution

• Punctuated Equilibrium

– evolution occurs in jumps and spurts

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THE TEMPO OF EVOLUTIONThe pace of evolution varies for different species. Some species have evolved gradually over time, while others spend vast amounts of time with little change.

GRADUAL CHANGEEvolution by creeps: The pace of evolution occurs gradually in incremental steps.

PUNCTUATED EQUILIBRIUMEvolution by jerks: Rapid periods of evolutionary change are punctuated by longer periods with little change.

Time

Time

Even though this period of rapid evolutionary change may only cover 1% of the species’ evolutionary history, it still may cover hundreds or thousands of generations. This could take tens of thousands of years in a primate or a matter of months in bacteria.