Great Ideas in Science:Great Ideas in Science:Lecture 13 – Evolving Lecture 13 – Evolving

systemssystemsProfessor Robert HazenProfessor Robert Hazen

UNIV 301UNIV 301

Life originated on Earth billions Life originated on Earth billions of years ago as a single cell, and of years ago as a single cell, and has been evolving by the process has been evolving by the process of natural selection ever since.of natural selection ever since.

Two Stages of EvolutionTwo Stages of Evolution

Chemical EvolutionChemical Evolution – – Lab experiments show Lab experiments show complex molecules complex molecules arise from simple onesarise from simple ones

Natural SelectionNatural Selection – – Once a reproducing Once a reproducing cell exists, complexity cell exists, complexity arises from arises from competitioncompetition

The Origin of Life:The Origin of Life:Four PossibilitiesFour PossibilitiesThe Origin of Life:The Origin of Life:Four PossibilitiesFour Possibilities

1.1. A miracle – an act of divine A miracle – an act of divine interventionintervention

2.2. An event consistent with An event consistent with chemistry and physics, but chemistry and physics, but extremely unlikelyextremely unlikely

3.3. An inevitable consequence of An inevitable consequence of chemistry, given an appropriate chemistry, given an appropriate environment and sufficient timeenvironment and sufficient time

4.4. Intelligent designIntelligent design

Chemical EvolutionChemical EvolutionChemical EvolutionChemical Evolution

Life arose by a natural process Life arose by a natural process of of ““emergent complexity,emergent complexity,””

consistent with natural laws.consistent with natural laws.

This hypothesis predicts This hypothesis predicts that life began as a that life began as a

sequence of chemical steps.sequence of chemical steps.

Intelligent DesignIntelligent DesignIntelligent DesignIntelligent Design

Life is Life is ““irreducibly complex.irreducibly complex.”” Therefore, a supernatural Therefore, a supernatural

designer must have formed it.designer must have formed it.

This hypothesis requires a This hypothesis requires a combination of natural and combination of natural and

supernatural processes.supernatural processes.

Is ID Science?Is ID Science?Is ID Science?Is ID Science?ON THE ONE HAND:ON THE ONE HAND:

ID makes predictions, albeit negative ones.ID makes predictions, albeit negative ones.

These predictions are falsifiable. These predictions are falsifiable.

BUT:BUT:ID is based on supernatural processes.ID is based on supernatural processes.ID is therefore inherently untestable, and isID is therefore inherently untestable, and is unsupported by observational evidence.unsupported by observational evidence.

THE THE ““DEBATEDEBATE””THE THE ““DEBATEDEBATE”” ““Both sides ought to be properly Both sides ought to be properly

taught ... so people can understand taught ... so people can understand what the debate is about.what the debate is about.”” G. W. Bush G. W. Bush

““Intelligent design should not be Intelligent design should not be taught in high school biology classes taught in high school biology classes

as an alternative to evolution.as an alternative to evolution.”” American Chemical SocietyAmerican Chemical Society

How Should Science How Should Science Respond to ID?Respond to ID?

How Should Science How Should Science Respond to ID?Respond to ID?

Design a research program that Design a research program that demonstrates the natural transition demonstrates the natural transition

from chemical simplicity to from chemical simplicity to emergent complexity. emergent complexity.

If biological complexity can be If biological complexity can be shown to arise spontaneously as shown to arise spontaneously as the result of natural processes, the result of natural processes,

then ID is unnecessary. then ID is unnecessary.

STONEHENGESTONEHENGESTONEHENGESTONEHENGE

What is Emergent Complexity?What is Emergent Complexity?What is Emergent Complexity?What is Emergent Complexity?

Emergent phenomena arise from interactions among numerous

individual particles, or “agents.”

The Emergence of Slime MoldThe Emergence of Slime MoldThe Emergence of Slime MoldThe Emergence of Slime Mold

ChemicalChemicalPotentialPotentialGradientsGradients

Dictyostelium

The Emergence of Slime MoldThe Emergence of Slime MoldThe Emergence of Slime MoldThe Emergence of Slime Mold

Dictyostelium

Emergent Phenomena – LifeEmergent Phenomena – LifeEmergent Phenomena – LifeEmergent Phenomena – Life

Central Assumptions ofCentral Assumptions ofOrigin-of-Life ResearchOrigin-of-Life ResearchCentral Assumptions ofCentral Assumptions ofOrigin-of-Life ResearchOrigin-of-Life Research

The first life forms were carbon-based.The first life forms were carbon-based.

LifeLife’’s origin was a chemical process s origin was a chemical process that relied on water, air, and rock.that relied on water, air, and rock.

The origin of life required a sequence The origin of life required a sequence of emergent steps of increasing of emergent steps of increasing complexity.complexity.

Four Emergent StepsFour Emergent StepsFour Emergent StepsFour Emergent Steps

1.1. Emergence of biomoleculesEmergence of biomolecules

2.2. Emergence of organized Emergence of organized molecular molecular systemssystems

3.3. Emergence of self-replicating Emergence of self-replicating molecular systemsmolecular systems

4.4. Emergence of natural selectionEmergence of natural selection

Emergence of BiomoleculesEmergence of Biomolecules

The strategy is to use simple moleculesto build larger molecules.

The Miller-Urey ExperimentThe Miller-Urey ExperimentThe Miller-Urey ExperimentThe Miller-Urey Experiment

Organic synthesis near the ocean-atmosphere interface.

Organic Synthesis in Interstellar “Dense”

Molecular Clouds

Organic Synthesis in Interstellar “Dense”

Molecular Clouds Experiments at NASA Ames simulate this environment.

The Hydrothermal The Hydrothermal HypothesisHypothesis

The Hydrothermal The Hydrothermal HypothesisHypothesis

A “BLACK SMOKER”

Deep-Sea VentsDeep-Sea VentsDeep-Sea VentsDeep-Sea Vents

Reactants:Reactants:

Pyruvic acid + COPyruvic acid + CO2 2

+ H+ H22OO

Conditions:Conditions:

200200ooCC

2,000 atm2,000 atm2 hours2 hours

Products: A Products: A diverse suite of diverse suite of organic moleculesorganic molecules

Self-Assembling Amphiphile Molecules

Minerals and Chiral SelectionMinerals and Chiral Selection

Mineral surfaces select chiral amino acids

The Emergence of Self-The Emergence of Self-Replicating Molecular CyclesReplicating Molecular Cycles

The Emergence of Self-The Emergence of Self-Replicating Molecular CyclesReplicating Molecular Cycles

The abiotic synthesis The abiotic synthesis of such a of such a ““metabolicmetabolic””

cycle represents a cycle represents a ““Holy GrailHoly Grail”” for our for our

experimental program.experimental program.

Prof. Harold J. Morowitz

The Emergence of Self-The Emergence of Self-Replicating Molecular CyclesReplicating Molecular Cycles

The Emergence of Self-The Emergence of Self-Replicating Molecular CyclesReplicating Molecular Cycles

The Emergence of The Emergence of Natural SelectionNatural Selection

The Emergence of The Emergence of Natural SelectionNatural Selection

The emergence of competition and

natural selection appears to be

inevitable in any self-replicating

molecular system in which some

molecules have the ability to mutate.

CONCLUSIONSCONCLUSIONSCONCLUSIONSCONCLUSIONS

The origin of life on Earth is best understood in terms of a sequence of emergent chemical events, each of which added a degree of structure and complexity to the prebiotic world.

While we don’t yet know all the details, there is no compelling evidence to suggest that life’s origin was other than a natural process.

Chemical Evolution:Chemical Evolution:The Window of OpportunityThe Window of Opportunity

Great Bombardment: Great Bombardment: Ended ~4 billion years agoEnded ~4 billion years ago

Oldest Fossils: Evidence Oldest Fossils: Evidence of life 3.5 billion years agoof life 3.5 billion years ago

The first cell probably The first cell probably arose 4.0-3.5 billion years arose 4.0-3.5 billion years agoago

Biological Evolution:Biological Evolution:The First CellThe First Cell

The first cell on EarthThe first cell on Earth Had no competitionHad no competition Multiplied rapidlyMultiplied rapidly

Special characteristicsSpecial characteristics 20 amino acids; DNA; 20 amino acids; DNA; RNARNA

Ability to mutate, and Ability to mutate, and thus evolvethus evolve

Three Definitions of Three Definitions of EvolutionEvolution

1.1. Evolution as ChangeEvolution as Change: Life : Life on Earth has changed over on Earth has changed over billions of years.billions of years.

2.2. Common Descent:Common Descent: All living All living things on Earth descended things on Earth descended from a common ancestor.from a common ancestor.

3.3. Natural Selection:Natural Selection: The The process by which life process by which life evolved is Darwinian evolved is Darwinian natural selectionnatural selection

First Definition of First Definition of Evolution: Change Over Evolution: Change Over

TimeTime Observational evidence overwhelmingly Observational evidence overwhelmingly

supports the theory that life originated supports the theory that life originated on Earth billions of years ago as a on Earth billions of years ago as a single cell, and has been changing ever single cell, and has been changing ever since.since.

FossilsFossils

Molecular BiologyMolecular Biology

Cellular biologyCellular biology

Comparative anatomyComparative anatomy

Observations of nature and of breedingObservations of nature and of breeding

Observational Evidence for Observational Evidence for an Ancient Earthan Ancient Earth

Annual events:Annual events: Tree ringsTree rings 15,000 years15,000 years Varve depositsVarve deposits >500,000 years>500,000 years Ice coresIce cores 1,200,000 years1,200,000 years

Radiometric dating Radiometric dating 4.5 x 104.5 x 1099 yearsyears

Geological ProcessesGeological Processes 101099 years years

Astronomical dataAstronomical data 10101010 years years

Half-LifeHalf-Life

The average time for The average time for

decay of ½ of a batch of decay of ½ of a batch of

radioactive isotopesradioactive isotopes

Wide range of half-livesWide range of half-lives Radon-222: 3.8 daysRadon-222: 3.8 days Carbon-14: ~5,700 yearsCarbon-14: ~5,700 years Uranium-234: 250,000 yearsUranium-234: 250,000 years Uranium-238: 4.5 billion yearsUranium-238: 4.5 billion years

Life has Changed over Life has Changed over Time: The Fossil RecordTime: The Fossil Record

FossilsFossils: Evidence of past : Evidence of past lifelife Tracks and trailsTracks and trails

OrganismOrganism’’s hard partss hard parts Turned to rockTurned to rock

Replaced by mineralsReplaced by minerals

Fossil recordFossil record Fossils found, catalogued & Fossils found, catalogued &

analyzedanalyzed

Shows transitionsShows transitions

Incomplete Incomplete

Life has Changed over Life has Changed over Time: The Fossil RecordTime: The Fossil Record

A few examples:A few examples: Horn coral – 500 million years Horn coral – 500 million years

oldold Trilobite – 350 million years oldTrilobite – 350 million years old Ammonites – 200 million years Ammonites – 200 million years

oldold Primitive shark tooth – 100 Primitive shark tooth – 100

million years oldmillion years old Whale bone – 15 million years Whale bone – 15 million years

oldold

FossilsFossils

StrataStrataYounger = higherYounger = higher

Extinct AnimalsExtinct Animals

TRILOBITESTRILOBITES

If you accept observational evidence, then the unambiguous

conclusion is that life has changed over time.

Calvert CliffsCalvert Cliffs15,000,000 m.y.15,000,000 m.y.

If you accept observational evidence, then the unambiguous

conclusion is that life has changed over time.

FossilsFossils Fossils prove that life on Earth Fossils prove that life on Earth

has changed over time; most are has changed over time; most are extinct.extinct.

Fossils demonstrate that these Fossils demonstrate that these changes are gradual and changes are gradual and progressive (simple to complex)progressive (simple to complex)

All known fossils fit into a pattern All known fossils fit into a pattern of continuous evolutionof continuous evolution..

The Story of LifeThe Story of Life

First cellFirst cell

EukaryotesEukaryotes

ColoniesColonies

Hard shells (the Hard shells (the Cambrian Cambrian explosion)explosion)

VertebratesVertebrates

PrimatesPrimates

HumansHumans

Geological TimeGeological Time

The Evolution of The Evolution of Human BeingsHuman Beings

Evidence from Anatomy:Evidence from Anatomy:Vestigial FeaturesVestigial Features

Vestigial featuresVestigial features Familiar structureFamiliar structure No useful functionNo useful function

ExamplesExamples Appendix: Appendix:

humanshumans Wings: penguinsWings: penguins Hind legs: whalesHind legs: whales

Evidence from Anatomy:Evidence from Anatomy:Homologous StructuresHomologous Structures

Compare forelimbs of vertebratesCompare forelimbs of vertebrates

How Did Evolution Occur?How Did Evolution Occur?Natural SelectionNatural Selection

Populations exhibit Populations exhibit variations.variations.

More individuals are More individuals are born than will born than will survive.survive.

The most fit The most fit individuals are more individuals are more likely to reproduce.likely to reproduce.