Great Ideas in Science: Lecture 13 – Evolving systems Professor Robert Hazen UNIV 301 Life originated on Earth billions of years ago as a single cell, and has been evolving by the process of natural selection ever since.

Two Stages of Evolution Chemical Evolution – Lab experiments show complex molecules arise from simple ones Natural Selection – Once a reproducing cell exists, complexity arises from competition

The Origin of Life: Four Possibilities 1. A miracle – an act of divine intervention 2. An event consistent with chemistry and physics, but extremely unlikely 3. An inevitable consequence of chemistry, given an appropriate environment and sufficient time 4. Intelligent design

Chemical Evolution Life arose by a natural process of “emergent complexity,” consistent with natural laws. Life arose by a natural process of “emergent complexity,” consistent with natural laws. This hypothesis predicts that life began as a sequence of chemical steps.

Intelligent Design Life is “irreducibly complex.” Therefore, a supernatural designer must have formed it. Life is “irreducibly complex.” Therefore, a supernatural designer must have formed it. This hypothesis requires a combination of natural and supernatural processes.

Is ID Science? ON THE ONE HAND: ID makes predictions, albeit negative ones. These predictions are falsifiable. BUT: BUT: ID is based on supernatural processes. ID is therefore inherently untestable, and is unsupported by observational evidence. unsupported by observational evidence.

THE “DEBATE” “Both sides ought to be properly taught... so people can understand what the debate is about.” G. W. Bush “Both sides ought to be properly taught... so people can understand what the debate is about.” G. W. Bush “Intelligent design should not be taught in high school biology classes as an alternative to evolution.” American Chemical Society American Chemical Society

How Should Science Respond to ID? Design a research program that demonstrates the natural transition from chemical simplicity to emergent complexity. If biological complexity can be shown to arise spontaneously as the result of natural processes, then ID is unnecessary.

STONEHENGESTONEHENGE

What is Emergent Complexity? Emergent phenomena arise from interactions among numerous individual particles, or “agents.”

The Emergence of Slime Mold ChemicalPotentialGradients Dictyostelium

The Emergence of Slime Mold Dictyostelium

Emergent Phenomena – Life

Central Assumptions of Origin-of-Life Research The first life forms were carbon-based. Life’s origin was a chemical process that relied on water, air, and rock. The origin of life required a sequence of emergent steps of increasing complexity.

Four Emergent Steps 1. Emergence of biomolecules 2. Emergence of organized molecular systems 3. Emergence of self-replicating molecular systems 4. Emergence of natural selection

Emergence of Biomolecules The strategy is to use simple molecules to build larger molecules.

The Miller-Urey Experiment Organic synthesis near the ocean-atmosphere interface.

Organic Synthesis in Interstellar “Dense” Molecular Clouds Experiments at NASA Ames simulate this environment.

The Hydrothermal Hypothesis A “BLACK SMOKER”

Deep-Sea Vents Reactants: Reactants: Pyruvic acid + CO 2 + H 2 O Conditions: Conditions: 200 o C 2,000 atm 2 hours Products: A diverse suite of organic molecules Products: A diverse suite of organic molecules

Self-Assembling Amphiphile Molecules

Minerals and Chiral Selection Mineral surfaces select chiral amino acids

The Emergence of Self- Replicating Molecular Cycles The abiotic synthesis of such a “metabolic” cycle represents a “Holy Grail” for our experimental program.

Prof. Harold J. Morowitz The Emergence of Self- Replicating Molecular Cycles

The Emergence of Natural 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.

CONCLUSIONSCONCLUSIONS 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: The Window of Opportunity Great Bombardment: Ended ~4 billion years ago Great Bombardment: Ended ~4 billion years ago Oldest Fossils: Evidence of life 3.5 billion years ago Oldest Fossils: Evidence of life 3.5 billion years ago The first cell probably arose billion years ago The first cell probably arose billion years ago

Biological Evolution: The First Cell The first cell on Earth The first cell on Earth Had no competition Had no competition Multiplied rapidly Multiplied rapidly Special characteristics Special characteristics 20 amino acids; DNA; RNA 20 amino acids; DNA; RNA Ability to mutate, and thus evolve Ability to mutate, and thus evolve

Three Definitions of Evolution 1. Evolution as Change: Life on Earth has changed over billions of years. 2. Common Descent: All living things on Earth descended from a common ancestor. 3. Natural Selection: The process by which life evolved is Darwinian natural selection

First Definition of Evolution: Change Over Time Observational evidence overwhelmingly supports the theory that life originated on Earth billions of years ago as a single cell, and has been changing ever since. Observational evidence overwhelmingly supports the theory that life originated on Earth billions of years ago as a single cell, and has been changing ever since. Fossils Fossils Molecular Biology Molecular Biology Cellular biology Cellular biology Comparative anatomy Comparative anatomy Observations of nature and of breeding Observations of nature and of breeding

Observational Evidence for an Ancient Earth Annual events: Annual events: Tree rings15,000 years Tree rings15,000 years Varve deposits>500,000 years Varve deposits>500,000 years Ice cores1,200,000 years Ice cores1,200,000 years Radiometric dating 4.5 x 10 9 years Radiometric dating 4.5 x 10 9 years Geological Processes10 9 years Geological Processes10 9 years Astronomical data10 10 years Astronomical data10 10 years

Half-Life The average time for The average time for decay of ½ of a batch of radioactive isotopes Wide range of half-lives Wide range of half-lives Radon-222: 3.8 days Radon-222: 3.8 days Carbon-14: ~5,700 years Carbon-14: ~5,700 years Uranium-234: 250,000 years Uranium-234: 250,000 years Uranium-238: 4.5 billion years Uranium-238: 4.5 billion years

Life has Changed over Time: The Fossil Record Fossils: Evidence of past life Fossils: Evidence of past life Tracks and trails Tracks and trails Organism’s hard parts Organism’s hard parts Turned to rock Turned to rock Replaced by minerals Replaced by minerals Fossil record Fossil record Fossils found, catalogued & analyzed Fossils found, catalogued & analyzed Shows transitions Shows transitions Incomplete Incomplete

Life has Changed over Time: The Fossil Record A few examples: A few examples: Horn coral – 500 million years old Horn coral – 500 million years old Trilobite – 350 million years old Trilobite – 350 million years old Ammonites – 200 million years old Ammonites – 200 million years old Primitive shark tooth – 100 million years old Primitive shark tooth – 100 million years old Whale bone – 15 million years old Whale bone – 15 million years old

Fossils Strata Younger = higher

Extinct Animals

TRILOBITES If you accept observational evidence, then the unambiguous conclusion is that life has changed over time.

Calvert Cliffs 15,000,000 m.y. If you accept observational evidence, then the unambiguous conclusion is that life has changed over time.

Fossils Fossils prove that life on Earth has changed over time; most are extinct. Fossils prove that life on Earth has changed over time; most are extinct. Fossils demonstrate that these changes are gradual and progressive (simple to complex) Fossils demonstrate that these changes are gradual and progressive (simple to complex) All known fossils fit into a pattern of continuous evolution. All known fossils fit into a pattern of continuous evolution.

The Story of Life First cell First cell Eukaryotes Eukaryotes Colonies Colonies Hard shells (the Cambrian explosion) Hard shells (the Cambrian explosion) Vertebrates Vertebrates Primates Primates Humans Humans

Geological Time

The Evolution of Human Beings

Evidence from Anatomy: Vestigial Features Vestigial features Vestigial features Familiar structure Familiar structure No useful function No useful function Examples Examples Appendix: humans Appendix: humans Wings: penguins Wings: penguins Hind legs: whales Hind legs: whales

Evidence from Anatomy: Homologous Structures Compare forelimbs of vertebrates

How Did Evolution Occur? Natural Selection Populations exhibit variations. Populations exhibit variations. More individuals are born than will survive. More individuals are born than will survive. The most fit individuals are more likely to reproduce. The most fit individuals are more likely to reproduce.