The History and Mechanisms of Evolutionary Theory

1. Evolution AP Biology Unit 4

2. History of Evolutionary Theory • Linnaeus • Developed a system of classification based on body structures (morphology) • Lamarck • Said species could “will” themselves to change Images taken without permission from http://65.107.211.206/victorian/science/lamarck.jpg and http://www.necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpg

3. History of Evolutionary Theory • Darwin • Main idea: Natural Selection causes species to change over time • Mendel • Genetics – now used as another way to look at evolution (similarities between DNA, RNA sequences) Img Src: http://www.panspermia.org/darwin.jpg

4. Natural Selection • 5 parts: • Population growth has the ability to be exponential (many offspring). • Populations tend to be stable in size (despite #1). • Resources are limited. • Individuals vary in phenotype (variations are random). • 5. Much phenotypic variation is heritable. Img Src: http://www.abc.net.au/nature/parer/img/galapagos.gif

5. Natural Selection (in summary) • There are more individuals produced than the environment can support  leads to competition for resources. • Individuals with advantageous traits in this competition will survive to reproduce and pass on those advantageous traits to the next generation.

6. Artificial Selection • Breeding animals or plants to have the desired traits • Ex. Dog & Cat breeds American curl cat Shar-Pei Great Dane Images taken without permission from http://www.caine.de.rasa.ham.8m.com/images/shar_pei.jpg, http://www.petsmart.com/aspca/images/dogs/great_dane.jpg, http://www.cfainc.org/breeds/profiles/articles/acurl.html ,

7. Newer developments in Artificial Selection • Cocker spaniel + poodle = Cockapoo • Labrador + Poodle = Labradoodle • Why mix with poodles? • Their fur tends to shed less– they were originally bred in an effort to create a guide dog for people who were allergic to dogs.

8. Bay Area Link… Luther Burbank • Developed MANY new (now famous) plants using artificial selection

9. Evidence for Evolution • Fossil record • Biogeography • Genetics • Similarities between organisms • Chemical • Anatomical

10. Vestigial Structures • Structures that are no longer used in an organism • Ex. Appendix, tail bone • Existence suggest common ancestry with other organisms • Many structures present in embryos are also used to show common ancestry -- developmental biology Img Src: http://www.vh.org/adult/provider/anatomy/AnatomicVariants/SkeletalSystem/Images/19.html

12. A fictional vestigial structure 

13. Analogous Structures • Similar functions, different structures • Indicates different ancestors • Ex. Bird wing, butterfly wing • Result from convergent evolution: similar selection pressures cause similar structures to evolve.

14. Homologous structures • Similar structure, different functions • Indicate a common ancestor • Ex. Human hand, seal flipper, bat wing

15. Biochemical comparisons • Common ancestry is also evident through similarities in biochemistry and genetic sequences • DNA nucleotide/gene • Protein sequences • Metabolic processes

16. Fossil Record • Fossils = preserved remains of ancient organisms • The fossil record allows scientists to observe changes on earth over time. • Fossils are dated using a variety of methods: • Age of rock fossil is found in • Decay of isotopes like C-14 • Relationships within phylogenetic trees

17. Biogeography • Study of distribution of organisms (past and present) • Demonstrate that organisms can evolve similarly to one another in similar environments from different ancestors • Ex. Marsupials in Australia – they are only found in Australia but some share similar characteristics with other organisms

18. How Evolution Occurs: Genetic Drift • Changes in the gene pool caused by random events • Examples: Bottleneck Effect, Founder Effect

19. Bottleneck Effect • drastic reduction in population (due to natural disasters, predators, etc.)

20. Example of Bottleneck Effect: Pingapalese People Img Src: http://www.genomenewsnetwork.org/articles/06_00/pingelapese_colorblind.shtml Img Src: http://www.7blueseas.com/destinations/images/map_southpacific.jpg

21. Example of Bottleneck Effect: Cheetahs Img Src: http://www.meerkats.com/images/cheetah-cub.jpg Img Src: http://easyweb.easynet.co.uk/~iany/patterns/images/cheetah.jpg

22. Founder Effect • A few individuals become isolated from the original population • The resulting population is NOT representative of the original population

23. Example of Founder Effect

24. Another Example of Founder Effect: Ellis-van Creveld Syndrome Img src: http://www.emedicine.com/ped/images/296682EVC-polydactylya.jpg Img Src: http://www.emedicine.com/ped/topic660.htm

25. Geographic Isolation • When physical separation/isolation results in the formation of new species • Is a cause of founder effect • Adaptive radiation = many species evolving from one original ancestor

26. Example of Geographic Isolation Img Src: http://www.desertfishes.org/na/cyprinod/cyprinod/cssalinu/cssalin1.jpg

27. Question… • What is the difference between bottleneck effect and founder’s effect? • Bottleneck effect and founders effect are both examples of genetic drift but what causes the drastic change in population and allelic frequencies is different.

28. Gene Flow ·  Migration (immigration, emigration) • Breeding across prior barriers (cultural barriers, for instance, as in human populations) • Changes allelic frequencies • Ex. Human migration

29. Phenotypic Polymorphism • Defined as variety of physical traits • Due to: • genetic variation (more general– an individual can have a variety of alleles) • genetic polymorphism (2 or more alleles exist for a gene) • nonheritable variation

30. Fitness ·  fitness = contribution of individual to gene pool, relative to others’ contributions ·  relative fitness = contribution of a genotype (all individuals alike) ·  fitness of 1 means you (or your genotype) contribute at a maximum (100%) • fitness of 0 means you (or your genotype) do not reproduce at all

31. Types of Selection • Selection = Environment chooses those with the best adaptations to survive

32. Stabilizing Selection = “middle” phenotype is selected for

33. Disruptive Selection • The two extremes are selected for • Ex. Snails

34. Directional Selection = one phenotype is selected for Img Src: http://web.nmsu.edu/~wboeckle/pepper_moth2.JPG Industrial melanism

35. Heterozygote Advantage • When being heterozygous gives you an advantage • Explains why a harmful recessive allele does not get eliminated from a population • Ex. Sickle cell anemia – heterozygotes are resistant to malaria Img Src: http://www.nidcd.nih.gov/news/releases/02/malaria.jpg Img Src: http://www.unomaha.edu/~swick/images/sickel.jpg

36. Sexual Selection • Genders appear different due to Sexual Dimorphism • Competition is intergender (compete for the opposite gender) and intragender (compete with each other) specific • Ultimately has to do with competition for higher fitness

37. Constraints on Natural Selection • Populations are not perfectly suited to their environments because • Environments constantly change (Ex. A storm destroys all of the fruit trees in an area. Animals and plants that previously were successful at eating these fruits are now at a disadvantage)

38. Constraints on Natural Selection • Populations are not perfectly suited to their environments because • Evolution is slow and new structures rarely form (Ex. Birds have 2 wings & 2 legs rather than 4 wings, (even though more wings could help with flight), because they evolved from a 4-appendage reptile; 2 wings and 2 legs)

39. Constraints on Natural Selection • Populations are not perfectly suited to their environments because • Adaptations are compromised (Ex. seal legs would help in land motion, but swimming with legs is less efficient than with flippers)

40. Constraints on Natural Selection • Populations are not perfectly suited to their environments because • Natural selection can only select for the best variation—it can’t create variations