Transcript Slideshow
Evolution AP Biology Essential Questions What is evolution? How does evolution work? What is the mechanism of evolution? How does natural selection work? What are the different variations of selection? What is the evidence for evolution? 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 History of Evolutionary Theory Darwin Natural Selection causes species to change Mendel – now used as another way to look at evolution Genetics Img Src: http://www.panspermia.org/darwin.jpg Natural Selection 5 parts: 1. Population growth has the ability to be exponential. 2. Populations tend to be stable in size (despite #1). 3. Resources are limited. 4. Individuals vary in phenotype. 5. Much phenotypic variation is heritable. Img Src: http://www.abc.net.au/nature/parer/img/galapagos.gif 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. Artificial Selection Breeding animals or plants to have the desired traits Ex. Dog & Cat breeds Great Dane Shar-Pei American curl cat 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 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. Vestigial Structures Structures that are no longer used in an organism Ex. Appendix, tail bone 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 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. Homologous structures Similar structure, different functions Indicate a common ancestor Ex. Human hand, seal flipper, bat wing 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 Genetic Drift Changes in the gene pool caused by random events Examples: Bottleneck Effect, Founder Effect, Geographic Isolation Bottleneck Effect drastic reduction in population (due to natural disasters, predators, etc.) 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 Founder Effect A few individuals become isolated from the original population The resulting population is not representative of the original population Example of Founder Effect 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 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 Example of Geographic Isolation Img Src: http://www.desertfishes.org/na/cyprinod/cyprinod/cssalinu/cssalin1.jpg Gene Flow Migration (immigration, emigration) Breeding across prior barriers (cultural barriers, for instance, as in human populations) Changes allelic frequencies Ex. Human migration Phenotypic Polymorphism Defined Due - as variety of physical traits to genetic variation genetic polymorphism nonheritable variation 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 Types of Selection Selection = Environment chooses those with the best adaptations to survive Stabilizing Selection = middle phenotype is selected for Disruptive Selection The two extremes are selected for Ex. Snails Directional Selection = one phenotype is selected for Img Src: http://web.nmsu.edu/~wboeckle/pepper_moth2.JPG Industrial melanism 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 Sexual Selection Genders appear different due to Sexual Dimorphism Competition is inter- and intragender specific Ultimately has to do with competition for higher fitness Constraints on Natural Selection Populations are not perfectly suited to their environments because Environments constantly change (Ex. A new population of people marooned from a breaking ship begin a new population. They do not necessarily represent the best of the gene pool) 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 rather than 4, which could help with flight, because they evolved from a 4-appendage reptile; 2 wings and 2 legs) 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) Constraints on Natural Selection Populations are not perfectly suited to their environments because Natural selection can only pick the best variation—it can’t create variations