Evolution

1. Evolution Origin of Life and Speciation

2. Spontaneous Generation • 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

3. Example #1 • 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

4. Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs

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

6. 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

7. Louis Pasteur (1822-1895)

8. Pasteur's Problem • 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

9. Pasteur's Experimental Results

10. The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis Figure 1.3

11. Early Earth • Early Earth was formed about 4.6 billion years ago and was very different than earth today. • How do you think it might have been different?

12. Early Earth • The atmosphere was very different than it is now, containing little or no oxygen. • Earth was too hot for liquid water. • Once the surface cooled enough for rocks to form, the surface was covered with volcanic activity.

13. Early Earth • About 3.8 billion years ago the Earth cooled enough for liquid water to remain. • Thunderstorms drenched the planet and oceans covered most of the surface.

14. Could organic molecules have evolved under these conditions? • In the 1950’s Stanley Miller and Harold Urey tried to simulate the conditions of early Earth. • They showed how several amino acids could be created under those conditions.

15. Miller and Urey’s Experiment • They passed sparks (representing lightening) through a mixture of hydrogen, methane, ammonia, and water (representing the atmosphere)

16. The Big Picture • Miller and Urey showed that the mixtures of organic compounds necessary for life could have arisen on primitive earth!

17. Hypothesis of the Origin of Life • The leap from a mixture of organic molecules to a living cell is large. • Tiny bubbles of organic molecules (called proteinoid spheres) have characteristics of living systems such as selectively permeable membranes and means of storing and releasing energy. They may have become more and more like living cells over time.

18. Hypothesis of the Origin of Life • Experiments have shown that under the conditions of early Earth, small RNA sequences could have formed and replicated on their own. This could have created a simple RNA-based form of life from which the DNA system could have evolved.

19. Hypothesis of Origin of Life • How certain do you think this hypothesis is? Do you think it will ever be changed? Do you think it will be changed during your lifetime?

20. Origin of Life • Evidence indicates that about 200-300 million years after the accumulation of liquid water on Earth, cells similar to modern bacteria were common.

21. Changing Earth • Photosynthetic bacteria became common and oxygen began to accumulate in the atmosphere and the ozone layer formed. • The rise in oxygen caused some life forms to go extinct, while others evolved ways to use oxygen for respiration.

22. Hypothesis of Origin of Eukaryotic Cells-Endosymbiotic Theory • What is a eukaryotic cell? • Prokaryotic cells began to evolve internal cell membranes- this was the ancestor to eukaryotic cells. • Smaller prokaryotes began living inside this ancestor and over time it became an interdependent relationship. What does this mean?

23. Endosymbiotic Theory • One group which entered the cell had the ability to use oxygen to generate ATP. These evolved into mitochondria. • Another group of prokaryotes which carried out photosynthesis evolved into chloroplasts.

24. Evidence for Endosymbiotic Theory • Mitochondria and chloroplasts have many characteristics of free living bacteria: 1- contain DNA similar to bacterial DNA 2- have ribosomes of similar size and structure to those of bacteria 3- reproduce by binary fission like bacteria

25. Speciation • Speciation: the formation of new species • What is a species? • As new species evolve, the populations become reproductively isolated from each other. (cannot interbreed and produce fertile offspring)

26. N. Selection of Polygenic traits • This changes the bell curve of polygenic expression. • Creates 3 types of selection • Directional selection • Stabilizing selection • Disruptive selection

27. Directional Selection Average organism do not survive. It can change the appearance of a population dramatically. Key Low mortality, high fitness Food becomes scarce. High mortality, low fitness

28. Stabilizing Selection Normal individuals have the best chance of surviving. Stabilizing Selection Selection against both extremes keep curve narrow and in same place. Key Low mortality, high fitness High mortality, low fitness Percentage of Population Birth Weight

29. Disruptive Selection Only organisms with extreme traits can survive. You create two different extremes phenotypes. Disruptive Selection Key Largest and smallest seeds become more common. Beak Size Beak Size Low mortality, high fitness Number of Birdsin Population Number of Birdsin Population Population splits into two subgroups specializing in different seeds. High mortality, low fitness

30. Isolating Mechanisms: • Behavioral Isolation: differences in courtship or reproductive strategies that prevent breeding • Geographic Isolation: populations separated by physical barriers • Temporal Isolation: reproduce at different times

31. Behavioral Isolation • This is when within a population, courtship behaviors change. • This splits how a species will reproduce creating a new gene pool. • Birds with different mating songs.

32. Geographic Isolation

33. Temporal Isolation • This is when species reproduce at different time. • I.e Orchids that flower at different times. • Morning Glories and Moon flowers

34. Patterns of Evolution • Adaptive Radiation: when a species evolves into several different forms that live in different ways • Can you think of an example we have discussed, or any other example, of adaptive radiation?

35. Patterns of Evolution • Example of adaptive radiation: Darwin’s finches-more than a dozen species evolved from a single species

36. Patterns of Evolution • Convergent Evolution: unrelated organisms come to resemble one another due to similar selective pressures • Example? • What is divergent evolution?

37. Patterns of Evolution • Coevolution: when two species evolve together, in response to changes in each other • Can you think of an example?

38. Coevolution • Example: flowers and pollinators, flowers and plant-eating insects

39. Gradual versus Punctuated Evolution Gradual: slow and steady change Punctuated: long, stabile periods interrupted by brief periods of rapid change

40. Can we see evolution occur? • Can you think of an example of an organism that evolves “quickly”? One that has evolved during your life time?

41. Bacterial EvolutionWhat allows bacteria to evolve so quickly?

42. Genetic Equilibrium • Most allele frequencies will stay constant. • Therefore populations will not evolve. • The Hardy-Weinberg principle can influence the gene pool. • You need five conditions to keep genetic equilibrium.

43. Five conditions • Random mating • Population must be large • No movement in or out or population. • No mutations • And no natural selection.