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Evolution History of Evolution The historical context of Darwin′s life and ideas. The dark blue bars above the timeline represent the lives of some individuals whose ideas have contributed to our modern understanding of evolution. Darwin • Naturalist (biology and geography) • 5 year mapping expedition of southern hemisphere. – Encountered organisms with different forms, yet similar to others in different parts of world. – Observed that the Earth changes. Galapagos Islands • Tortoises: Shell form and neck length varied from island to island. – These giant tortoises are found nowhere else in world. Yet three varieties exist that are locally adapted. Galapagos Islands • Finches: Beaks varied from island to island. – Realized that these variations were adapted for different food sources. – Suggested that 1 ancestral species could give rise to many different species Darwin’s Idea While rewriting his notes, came up with a process for how these changes could develop. Natural Selection 1. Members of a population have heritable variations Natural Selection 2. Individuals w/in a population will overproduce their offspring. 3. Certain individual’s variations will be better suited for that environment, and therefore be more likely to survive & reproduce better than those without. Natural Selection 4. Increased portion of population will have those variations after many generations with that particular environmental pressure. 5. This results in population that are adapted to local environment. Natural Selection Struggle for existence: • Limiting resources; not enough for all members of a population to survive. – Therefore organisms differ in their fitness = how many offspring an organism produces that survive to reproduce themselves. – “survival of the fittest” – Fitness is directionally proportional to the organisms adaptations Natural selection results in Adaptations Any heritable trait that aids in the survival and reproductive success of an organism. Types • Structural • Behavioral • Physiological: biochemical Structural Behavioral Physiological Artificial Selection When humans (not envt.) select desired traits. • Domesticated animals, crops, pets, ourselves. Evidence for Evolution Earth is 4.6 billion years old and the oldest evidence of life found is 3.6 billion years old. If this process has been shaping the organisms on this planet, then there should be evidence of it occurring. Evidence for Evolution Fossil Record: Skeletons, bones, impressions, etc. of organisms no longer found living on the planet. • Radiometric dating (carbon, potassium) suggests life billions of years old. • Activity • The older the fossils the more simple and the greater the differences between existing organisms. • Incomplete and includes inferences Evidence for Evolution Biogeographical: The study of the geographic distribution of organisms. • Islands of the world have species found no place else. (13 different species of finch on Galapagos, aquatic iguanas, Hawaiian honeycreepers, etc.) • Marsupials found in both Australia and S. America. Few placental mammals in Aus; many in S. America. Results in a wide diversity of marsupials in Australia and low diversity of marsupials in S. America. • Organisms that are similar on different continents are that way b/c adapted to similar ecosystems. Evidence for Evolution Anatomical: Outside appearance of body parts of similar categories of organisms may look and function differently. • If internal structures are examined lots of similarities exist. • Ex. Forelimbs in vertebrates Anatomical Evidence Con • Homologous Structures: Structures in different species that are similar in makeup, and may have different functions. • Wings of bat, forelimbs of dog. • Analogous Structures: Structures in different species that have different makeup but have same function. • Wings of bat and wings of bee • Vestigial Structures: Any structure that is reduced in function. • Results in reduction of size. (ex. Appendix, whale pelvic bones, ostrich wings.) Evidence for Evolution Genetic Comparisons: Comparing the base pairs, and amino acid sequences of different organisms. • The more similarities the closer related. • 60% of human genes are fundamentally the same as a fruit fly. • 90% same as mice • 96% similar to chimpanzees • All humans are 99.9% the same genetically