Chapter 15: Evolution—Evidence and Theory

1. Chapter 15: Evolution—Evidence and Theory 15-1 The Fossil Record 15-2 Theories of Evolution 15-3 Evolution in Process

2. 15-1 The Fossil Record I. Nature of Fossils (physical EVIDENCE for evolution) • Organisms appeared, LASTED for periods of time, BUT disappeared. • NOTE: MICROSCOPY  Too much DETAIL for fossils to be simple rock formations (Robert Hooke, 1700s).

4. (1) Fossil (e.g., Types: sedimentary fossils, molds and casts) • TRACE of a dead organism, usually with HARD MINERALS replacing tissues of an organism (leaving ROCK-LIKE structures).

6. (2) Sediment (fossils form INSIDE sedimentary rock) • Dust, sand, OR mud deposited in LAYERS by wind or water; • NOTE: Traps the HARDEST body parts of an organism to become fossilized (shell, bones, teeth, woody stems).

7. (3) Mold • HOLLOW fossil formed by sediment ENCASING a dead organism— becomes filled with HARD minerals, forming a CAST of an organism.

8. (4) Cast • Rock-like MODEL of an organism resulting from a MOLD filled in with HARD minerals.

9. II. Distribution of Fossils (Nicholas Steno, 1669) • Earth’s GEOLOGICAL and BIOLOGICAL history are recognized by Steno’s Law of Superposition.

10. (1) Law of Superposition • SUCCESSIVE layers of sediment are deposited on TOP of one another by wind and water  GEOLOGICAL STRATA.

11. (2) Stratum (pl. strata) • Geological layer showing its RELATIVE age with respect to OTHER strata above (YOUNGER) and below (OLDER).

13. (3) Relative Age (estimates VARY due to DEPOSITION and EROSION) • Age with respect to OTHER strata based upon its POSITIONING; (also can infer the AGE of the FOSSILS contained).

14. Critical Thinking (1) What may you be able to conclude if you find identical examples of a fossilized organism in TWO adjacent geological strata?

15. (4) Absolute Age (a form of quantitative data) • Determined by RADIOACTIVE DATING of materials isolated from within a stratum.

16. (A) Succession of Forms (Prokaryotes  Modern Humans) • Fossil-bearing strata show species have CHANGED over time, possibly becoming EXTINCT (replaced) by newer forms.

17. (1) Extinct (opposite = extant) • NO LONGER present due to SELECTIVE PRESSURES and confirmed through fossilized remains.

18. (2) Mass Extinction (fossil evidence) • Period where LARGE numbers of species disappeared due to DRASTIC environmental pressures. • (i.e., Widespread volcanic activity, or asteroid impacts (ash & dust theory))

20. (B) Biogeography (Extinct VS. Extant) • NEW organisms ARISE in environments where SIMILAR forms already inhabit (shared selective pressures yield similar phenotypes).

27. 15-2 Theories of Evolution I. Jean Baptiste de Lamarck’s Explanation (of HOW species change—1800s) • Claimed ACQUIRED traits COULD be passed on to offspring (i.e., Theory of Acquired Characteristics).

29. (1) Acquired Traits (CANNOT be passed down) • Are NOT determined by genes BUT by the ENVIRONMENT.

30. Critical Thinking (2) If a favorable trait INCREASES the lifespan of an organism WITHOUT affecting reproductive success, does it contribute to EVOLUTION?

32. II. The Beginning of Modern Evolutionary Thought (Darwin and Wallace) • GENETIC traits (NOT acquired traits) could be PASSED DOWN from parent to offspring via genes.

33. (1) Natural Selection (drives the process of EVOLUTION) • Individuals BEST adapted will reproduce MORE thus OVER time, MOST FIT are those with MOST offspring.

34. Critical Thinking (3) The process of natural selection throughout the history of life on Earth has resulted in the success of some species and the extinction of other species. Why has natural selection NOT resulted in the existence of a SINGLE best-adapted species?

35. (2) Population (SMALLEST unit CAPABLE of evolving) • Interbreeding group of same species; (e.g., a population’s GENE POOL consists of the TOTAL ALLELES held by that species).

36. (A) Charles Darwin (1831-1836—H.M.S. Beagle) • Naturalist collected DATA on species of around the world—interested in BIODIVERSITY and GEOGRAPHY.

38. (B) Voyage of the Beagle (5 years, WIND-driven ship) • A book (Principles of Geology)—influenced Darwin on the principles of UNIFORMITARIANISM.

39. (1) Uniformitarianism (e.g., fossils of seashells in the mountains) • Earth’s HABITATS have been SHAPED (changed) through SLOW processes that operate OVER time. NOTE: This influenced Darwin to believe modifications of ENVIRONMENTS required LONG periods of time, much like the CHANGES it would take SPECIES to ADAPT to these CHANGES (i.e., speciation).

40. (C) Analysis of Darwin’s Data (on geography AND biodiversity) • Supported “adaptive radiation” of FINCH and TORTOISE populations that dispersed over Galapagos Islands (West of S. America).

45. (D) Publication of The Origin of Species (1859) • Used data to propose 2 THEORIES supporting “HOW” the process of EVOLUTION occurs in a population.

46. III. Darwin’s Theories (following 5 year H.M.S. Beagle voyage) • Theory 1: DESCENT WITH MODIFICATION, occurs with EVERY species. • Theory 2: MODIFICATION BY NATURAL SELECTION drives EVOLUTION to occur.

47. (A) Descent with Modification • NEWER forms are the MODIFIED DESCENDANTS of OLDER species. (i.e., All species have DESCENDED from ONE or a FEW ORIGINAL types of life; remote, COMMON ANCESTORS are common to many species).

49. (B) Modification by Natural Selection (requires a DIVERSE gene pool) • NATURAL forces ACT UPON the GENETIC VARIATION within a population (resulting in VARYING degrees of FITNESS).

50. DARWIN’S THEORY OF EVOLUTION HOLDS FOUR TENETS (influenced by colleague Thomas Malthus) (1) Populations will naturally grow BEYOND the environmental capacity leading to a STRUGGLE for existence (Malthus’s work with populations). (2) Individuals within a POPULATION show VARIATION due to mutations AND genetic recombination. (3) The VARIATION is ACTED UPON (natural selection) allowing MOST FIT members to survive and YIELD MORE OFFSPRING. (4) Over TIME (and through evolution), the gene frequencies (i.e., GENE POOL) of the population WILL CHANGE (and thus, traits WILL CHANGE).