1. Great Ideas in Science: Lecture 13 – Evolving systems
Professor Robert Hazen
PROV 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.

2. 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

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

4. Chemical Evolution
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.

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

6. THE “DEBATE”
“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

7. 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.

8. STONEHENGE

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

12. The Emergence of Slime Mold
Chemical
Potential
Gradients
Dictyostelium

13. The Emergence of Slime Mold
Dictyostelium

14. Emergent Phenomena – Life

15. 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. Life’s origin required a sequence of emergent steps of increasing complexity.

16. Four Emergent Steps Emergence of biomolecules
Emergence of organized molecular systems
Emergence of self-replicating molecular systems
Emergence of natural selection

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

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

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

20. The Hydrothermal Hypothesis
A “BLACK SMOKER”

21. Deep-Sea Vents Reactants: Pyruvic acid + CO2 + H2O Conditions: 200oC
2,000 atm
2 hours
Products: A diverse suite of organic molecules

22. Self-Assembling Amphiphile Molecules

23. Self-Assembling Amphiphile Molecules

24. Minerals and Selection Mineral surfaces select amino acids

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

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

27. The Emergence of Natural Selection
The emergence of natural selection appears to be inevitable in any system of molecules that makes copies of itself.

28. CONCLUSIONS
The origin of life on Earth is best understood in terms of a sequence of emergent chemical events.
Each step added a degree of structure and complexity to the prebiotic world.
No compelling evidence exists to suggest that life’s origin was other than a natural process.

29. Chemical Evolution: The Window of Opportunity
Great Bombardment: Ended ~4 billion years ago
Oldest Fossils: Evidence of life 3.7 billion years ago
The first cell probably arose billion years ago

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

31. 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.
Fossils
Molecular Biology
Cellular biology
Comparative anatomy
Observations of nature and of breeding

32. Observational Evidence for an Ancient Earth
Annual events:
Tree rings 15,000 years
Varve deposits >500,000 years
Ice cores 1,200,000 years
Radiometric dating 4.5 x 109 years
Geological Processes 109 years
Astronomical data years

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

34. Life has Changed over Time: The Fossil Record
Fossils are any evidence of past life.
They include tracks and trails.
Most commonly an organism’s hard parts:
Bones, teeth, and shells are preserved in rock.
Hard parts are often replaced by minerals.
The Fossil Record is all fossils found, catalogued, & analyzed.
Taken together, they show transitions.
But the fossil record is very incomplete.

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

36. Fossils
Strata
Younger = higher

37. Extinct Animals

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

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

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

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

42. Geological Time

43. Evidence from Anatomy: Vestigial Features
Adaptive features—modified functions.
Vestigial features—familiar structures with no useful function.
Human appendix
Hind legs of whales

44. Evidence from Anatomy: Homologous Structures
Compare forelimbs of vertebrates

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