1. Evolution Chapter 25 Great Idea: All life on Earth evolved from single-celled organisms by the process of natural selection.

2. Chapter Outline • The Fact of Evolution • Chemical Evolution • Natural Selection and the Development of Complex Life • The Evolution of Human Beings

3. How did life start- origin of life. • How did the astonishing variety of life that we observe come about. • Fossil record. • Fossils- minerals replace the natural materials of the “hard parts” of organisms. • Mass extinction. • Genetics

4. The Origin of Life What are the properties of living systems? 1. Self duplication with information transfer. 2. Discrete change. Living systems are systems that reproduce themselves closely, but that mutate as well and can reproduce their mutations.

5. The word evolution simply means a change in genetic content. Populations evolve but individuals do not.

6. The Fact of Evolution

7. The Fact of Evolution • Evolution • Ongoing process of change • Scientists accept evolution as fact • Debate various theories

8. There are two approaches to tracing species: 1. Examine the fossil record - Paleontology 2. Examine the genes of living organisms - Molecular genetics

9. The Fossil Record • Fossils • Organism’s hard parts preserved • Turned to rock • Replaced by minerals • l • Fossil record • Fossils found, catalogued & analyzed • Shows transitions • Incomplete • Three key ideas • Older fossils more different • Increasing complexity with time • Most species have gone extinct

19. The Biochemical Evidence • DNA • Evidence for evolution • Changes slowly • Also compare amino acid sequences • Cytochrome C • Humans and chimps identical • Rattlesnake 86% overlap

20. Evidence from Anatomy:Vestigial Organs • Vestigial organs • Internal features • No useful function • Example • Appendix: humans • Wings: penguins • Hind legs: whales

21. Chemical Evolution

22. Life requires: Carbon, Nitrogen, Oxygen, Hydrogen Reducing Atmosphere: Carbon - CH4 Nitrogen - NH3 Hydrogen, Oxygen - H2O Non-reducing Atmosphere: Carbon - CO2 Nitrogen - N2 Hydrogen, Oxygen - H2O

24. There are considerable questions regarding the atmosphere of the primitive Earth. It is clear that there was no free oxygen. Free oxygen did not occur until living organisms evolved photosynthesis.

25. The Miller-Urey experiment. Several of the chemical compounds thought to have been present on the early Earth were mixed and subjected to electrical discharges. Within a few weeks, amino acids had formed. The spark is like lightning!

26. Stanley Miller's experiment, (1953) The spark is like lightning! Carbohydrates, bases, and amino acids formed

27. Some Origin of Life Scenarios 1. Life began in hydrothermal vents 2. Inorganic catalysis was important a. Clay minerals were the first living things b. Nitrogen fixation by oxides 3. Extraterrestrial origin of life

28. RNA Enzymes • Early life was simpler • RNA catalyzed reactions • Created proteins • Proteins led to DNA

29. The Window of Opportunity • Chemical processes • Occurred rapidly • Recent discoveries • Schopf • Evidence of life 3.5 billion years ago • First Cell • 4.0-3.5 billion years ago

30. The First Cell • First cell • No competition • Multiplied rapidly • Special characteristics • 20 amino acids

31. Black Smokers • Black Smokers • Deep-ocean floor • Vents of mineral rich hot water • Diverse ecosystem • Most primitive bacteria • Hydrothermal zones • Site of life’s origin? • Protected • Ideal chemical environment

32. Life three miles deep at a mid-Atlantic hydrothermal vent.

38. Natural Selection and the Development of Complex Life

39. Charles Darwin proposes natural selection.

40. Natural Selection • Darwin • Natural Selection • Variation in populations • Some variation heritable • More individuals born than will survive • Adaptation • Artificial selection

42. The Story of Life • First cell • Natural selection • mutations • Mutations • Most not beneficial • Environment • Impacts evolution • Eukaryotes • Colonies • Hard Shell • Cambrian explosion

43. Geological Time

44. Punctuated Equilibria

45. Mass Extinctions and the Rate of Evolution • Rate of extinction • 10%-20% extinct in 5-6 million years • Mass extinctions • 30%-90% extinct • Mechanisms • asteroid • Evolution • Gradualism • Punctuated equilibrium

46. Gradualism

47. Mass extinction The geological record show a number of instances in which the number of different species dropped dramatically These are mass extinctions brought about by some change in the environment: Meteor impact Global climate change Glaciation (Ice ages) Continental Drift Global warming (rise in sea levels)

48. The diversity of life on Earth has not increased steadily, but has gone through a series of sharp changes. This graph of marine animals in the fossil record is indicative of the overall growth in families and of extinctions. The extinction of the dinosaurs is labeled 5.

49. The location of the giant crater near the Yucatán Peninsula in Mexico. The effects of the asteroid’s impact were recorded in rocks as far away as the red dashed circle.