Spontaneous Generation vs. Biogenesis Honors Biology

1. Spontaneous Generation vs. BiogenesisHonors Biology

2. Aristotle (384 - 322 BC) • Proposed the theory of spontaneous generation • Also called abiogenesis • Idea that living things can arise from nonliving matter • Idea lasted almost 2000 years

4. Early Science • For centuries, people based their beliefson their interpretations of what they saw going on in the world around them without testing their ideas • They didn’t use the scientific method to arrive at answers to their questions • Their conclusions were based on untested observations

5. Example of Observations • Observation:Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times

6. Example cont… • Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs

7. John Needham By 1745 an English scientist used microscopic observations to support the theory of abiogenesis. To test the theory he boiled meat broth for several minutes in a loosely sealed flask. ( allow to cool down the flask) Immediately after boiling he saw under the microscope that the broth had no living things. After a few days he examined the flask and found microrganism.

8. John Needham Abiogenesis Microorganisms

9. Disproving Spontaneous Generation

10. Francesco Redi (1668) • In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat

11. Redi’s Experiment • Redi used open & closed flasks which contained meat. • His hypothesiswas that rotten meat does not turn into flies. • He observedthese flasks to see in which one(s) maggots would develop.

12. Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

13. Redi’s Findings • He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within. • In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.

14. Did Redi Use the Scientific Method?

15. LazzaroSpallanzani’s (1765) • Boiled soups for almost an hour and sealed containers by melting the slender necks closed. • The soups remained clear. • Later, he broke the seals & the soups became cloudy with microbes.

16. Spallanzani’s Results

17. Conclusion • Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “vital force” • “Vital force” needed to life to form. • Therefore, spontaneous generation remained the theory of the time

18. Needham 1745 Spallanzani 1765

19. Louis Pasteur (1822-1895)

20. Pasteur's Experiment • Hypothesis:Microbes come from cells of organisms on dust particles in the air; not the air itself. • Pasteur put broth into several special S-shaped flasks • Each flask was boiled and placed at various locations

21. Pasteur's Experiment - Step 1 • S-shaped Flask • Filled withbroth • The special shaped was • intended to trap any dust particles containing • bacteria

22. Pasteur's Experiment - Step 2 • Flasksboiled • Microbes Killed

23. Pasteur's Experiment - Step 3 • Flask left at various locations • Did not turn cloudy • Microbes not found • Notice the dust that collected in the neck of the flask

24. Pasteur's Experimental Results

25. The Theory of Biogenesis1864 • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis

26. Review Mr. Velázquez Biology

27. Evidence Pro and Con • 1668: Francisco Redi filled six jars with decaying meat. Conditions: Results: 3 jars covered with fine net - No maggots 3 open jars - Maggots appeared From where did the maggots come? What was the purpose of the sealed jars? Spontaneous generation or biogenesis?

28. Evidence Pro and Con • 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks.

29. Evidence Pro and Con • 1861: Louis Pasteur demonstrated that microorganisms are present in the air.

30. Evolution • Biological evolution • Descent with modification • small-scale evolution • (changes in gene frequency in a population from one generation to the next) • large-scale evolution • (the descent of different species from a common ancestor over many generations).

31. Chemical Evolution

32. Organic Evolution • Sequence of events involved in the evolutionary development of a species or taxonomic group of organisms

33. Aerobic heterotrophs & Photosynthetic autotrophs

35. Lamarck • 1801 • Theory of Acquired Characteristics • Elephants • Humans • Giraffes • Evolution is a predestined plan • Results decided

36. Darwin • Organisms are all different • Those with variations which help them survive in their environment will survive & reproduce • Those that aren’t able to adapt to their environment die off • No plan for evolution

37. Darwin • Natural Selection • Species that have adapted characteristics which are favorable to their environment pass those adaptations on to their offspring • Survival of the fittest • individuals adapted to environment will survive…speciation…changes to a species over time • Survival of the fittest is meant in terms of the environment… • Basis for Natural Selection or how evolution occurs over time

38. Types of Selection • Stabilizing Selection • Favors average phenotype and selects against the extreme • Seen with mice and robins • Disruptive / Diversifying Selection • Select for two or more phenotypes which have an advantage • Intermediate phenotypes are less fit than extremes • Seen in species with multiple male mating partners (lobster) • Directional Selection • Selection for one end of spectrum or the other based on environmental changes • Peppered moths

42. Mechanisms of Change • Mutation • A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. • That would make genes for brown coloration more frequent in the population than they were before the mutation.

43. Mechanisms for Change • Migration • Some individuals from a population of brown beetles might have joined a population of green beetles. • That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it.

44. Mechanisms for Change • Genetic Drift • Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. • Several green beetles were killed when someone stepped on them and had no offspring. • The next generation would have a few more brown beetles than the previous generation — but just by chance. • These chance changes from generation to generation are known as genetic drift.

45. Courtship Rituals • Sexual Dimorphism • Males v Females

46. Types of equilibrium • Punctuated • Gradualism • Catastrophism

47. Punctuated Equilibrium • Once species appear in the fossil record they will become stable, showing little net evolutionary change for most of their geological history.

48. Gradualism • slow accumulation of subtle changes

49. Catastrophism • Earth has been affected by sudden, short-lived, violent events that were sometimes worldwide in scope.  • Great Flood • Asteroid & Extinction of Dinosaurs

50. Malthus • Principle of Population • hunger and disease were aspects of life implemented by God to stop populations from exploding • competitive nature of life  • Thomas Malthus warned that population growth would exceed resourcegrowth • Without population control, the population would be reduced by catastrophes such as famine or war according to Malthusian theory.