Unit 5 evolution by natural selection

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  • 1. EVOLUTION BY NATURAL SELECTION CAMPBELL AND REECE, 2010 CHAPTER 22

2. ORIGIN OF IDEAS ABOUT ORIGINS DIFFERENT KINDS OF EVIDENCE EXIST: 1. Fossil records 2. Modification by descent and Homology 3. Biogeography 4. Genetics 3. 1. FOSSIL RECORDS (P. 453-454, 461-462) The study of fossils helped to lay the groundwork for Darwins ideas Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata. The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time 4. FOSSILS FOUND IN SEDEMENTARY ROCK 5. 2. MODIFICATION BY DESCENT AND HOMOLOGY (P.463-465) Homology is similarity resulting from common ancestry. Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor. 6. MAMMALIAN FORELIMBS: HOMOLOGOUS STRUCTURES 7. Comparative embryology reveals anatomical homologies not visible in adult organisms 8. Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor. Modification by descent is explained by: Convergent evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups. Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry. 9. CONVERGENT EVOLUTION 10. 3. BIOGEOGRAPHY Darwins observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution. Islands have many endemic species that are often closely related to species on the nearest mainland or island. Earths continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift. An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved. 11. PANGAEA CONTINENTAL DRIFT 12. DIFFERENCE BETWEEN HYPOTHESIS AND THEORY Hypothesis: A tentative answer to a well-framed question, narrower in scope than a theory, and subject to testing. Theory: An explanation which is broad in scope, and is supported by a large body of evidence. 13. OVERVIEW OF THE HISTORY OF DIFFERENT THEORIES OF DEVELOPMENT Spontaneous creation Ontogeny Lamarckism Neo Darwinism Punctuated Equilibrium 14. THEORY OF SPONTANEOUS CREATION/ GENERATION The theory of spontaneous generation held that complex, living organisms may be produced from nonliving matter. It was a popular belief that mice occur spontaneously from stored grain, or maggots spontaneously appear in meat. 15. THE THEORY OF ONTOGENY Ontogeny is the origin and development of an individual organism from embryo to adult. Within biology, ontogeny pertains to the developmental history of an organism within its own lifetime, as distinct from phylogeny, which refers to the evolutionary history of species 16. LAMARCKISM Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics. The mechanisms he proposed are unsupported by evidence. 17. EXAMPLE USED TO EXPLAIN LAMARCKISM THEORY Giraffes stretching their necks to reach leaves high in trees (especially Acacias), strengthen and gradually lengthen their necks. These giraffes have offspring with slightly longer necks (also known as "soft inheritance"). 18. NEO DARWINISM Darwinism as modified by the findings of modern genetics, stating that mutations due to random copying errors in DNA cause variation within a population of individual organisms and that natural selection acts upon these variations. 19. PUNCTUATED EQUILIBRIUM (P. 502) The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear Niles Eldredge and Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species existence. 20. PUNCTUATED CHANGE VS. GRADUAL CHANGE 21. CHARLES DARWIN: THE FATHER OF EVOLUTION 22. DARWINS RESEARCH As a boy and into adulthood, Charles Darwin had a consuming interest in nature Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle 23. DARWINS: VOYAGE OF THE BEAGLE During his travels on the Beagle, Darwin collected specimens of South American plants and animals He observed adaptations of plants and animals that inhabited many diverse environments. His interest in geographic distribution of species was kindled by a stop at the Galpagos Islands near the equator west of South America. 24. VOYAGE ROUTE OF THE BEAGLE 25. DARWINS FOCUS ON ADAPTATION In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes From studies made years after Darwins voyage, biologists have concluded that this is indeed what happened to the Galpagos finches 26. BEAK VARIATION IN GALAPAGOS FINCHES 27. DARWINS BOOK: ON THE ORIGIN OF SPECIES Darwin developed two main ideas: Descent with modification explains lifes unity and diversity Natural selection is a cause of adaptive evolution 28. Darwin never used the word evolution in the first edition of The Origin of Species The phrase descent with modification summarized Darwins perception of the unity of life. The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past. In the Darwinian view, the history of life is like a tree with branches representing lifes diversity 29. ARTIFICIAL SELECTION Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection. 30. THESE DIFFERENT VEGETABLES HAVE ALL BEEN SELECTED FROM ONE SPECIES OF WILD MUSTARD. BY SELECTING VARIATIONS IN DIFFERENT PARTS OF THE BR PLANT, BREEDERS HAVE OBTAINED THESE DIVERGENT RESULTS. 31. Darwin then described four observations of nature and from these drew two inferences; 1. Observation 1: Members of a population often vary greatly in their traits.2. Observation 2: Traits are inherited from parents to offspring. 3. Observation 3: All species are capable of producing more offspring than the environment can support. 4. Observation 4: Owing to lack of food or other resources, many of these offspring do not survive. 32. Inference 1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to have more offspring than other individuals. Inference 2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favourable traits in the population over generations. 33. NATURAL SELECTION Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals Natural selection increases the adaptation of organisms to their environment over time If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species 34. EXAMPLES OF EVOLUTIONARY ADAPTATION: CAMOPHLAGE 35. Note that individuals do not evolve; populations evolve over time Natural selection can only increase or decrease heritable traits in a population Adaptations vary with different environments. 36. FORMATION OF NEW SPECIES Speciation: the origin of new species. Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level. 37. BIOLOGICAL SPECIES CONCEPT The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations. 38. SPECIATION Speciation can occur in two ways: Allopatric speciation Sympatric speciation 39. ALLOPATRIC SPECIATION In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations. (barriers separate them) The definition of barrier depends on the ability of a population to disperse. Separate populations may evolve independently through mutation, natural selection, and genetic drift. In allopatric speciation, geographic isolation restricts gene flow between populations 40. Regions with many geographic barriers typically have more species than do regions with fewer barriers Allopatric speciation of antelope squirrels on opposite rims of the Grand Canyon Reproductive isolation between populations generally increases as the distance between them increases. 41. SYMPATRIC SPECIATION In sympatric speciation, speciation takes place in geographically overlapping populations Sympatric speciation can also result from the appearance of new ecological niches For example, the North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees. 42. In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species. Sympatric speciation can result from polyploidy, natural selection, or sexual selection. 43. REPRODUCTIVE ISOLATION Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring. Hybrids are the offspring of crosses between different species 44. MECHANISMS OF REPRODUCTIVE ISOLATION Breeding at different time