Descent With Modification: A Darwinian View of Life

1. Descent With Modification:A Darwinian View of Life

2. What is Evolution? The change in gene frequencies in a population over time

4. What is evolution? • Organism evolution means changes in populations, species, or groups of species. It occurs because: • Populations vary by the frequency of heritable traits that appear from one generation to the next. • These traits are represented by alleles for genes that modify morphology (form/structure), physiology, or behavior. • There is a struggle for survival and most organisms perish. Only those that survive pass their genes on.

5. Can individuals Evolve? • NO. Individuals can BE different and can survive and pass those genes on or be killed and not. • For an organism to change itself to suit its environment it would need to change the genes (DNA) inside every cell of it’s body. • Most importantly, they would need to change the DNA in their gametes- so the “change” could be passed on to the next generation. • Some individuals are better suited for their environment. They leave more offspring. Over generations, the genetic composition of a population reflects more of their “beneficial” genes.

6. Historical Context of Evolutionary Theory Paradigm shift from organisms are STATIC to the idea that organisms can CHANGE FORM. • Plato (427-347 B.C.) Two worlds: real/ideal world that is eternal and world of imperfection we perceive through senses. Living things were created in their perfect, static form by the gods. • Aristotle (384-322 B.C.) “scale of nature” all living forms could be arranged on. Each form assigned a rung, all rungs were taken.

7. LADDER OF LIFE Aristotle’s "steps of nature," or the "hierarchy of nature”…

8. Tree of Life instead of a ladder or hierarchy… tips of branches

9. Natural theology A philosophy dedicated to discovering the Creator’s plan by studying nature- the earth and it’s inhabitants. • Adapations were evidence that the Creator had designed each and every species for a particular purpose. • Classifying species was a major objective.

10. Carolus Linnaeus (1707-1778) • Specialized in taxonomy- naming and classifying the diverse forms of life. • Developed binomial nomenclature- a two part naming system. • Developed a system of grouping similar species into a hierarchy of increasingly general categories. (species- genus- family) • He saw no evolutionary relationships in his groupings.

11. Georges Cuvier (1769-1832) • Largely developed paleontology- the study of fossils. • Opposed to the idea of evolution. • Advocated catastrophism, the principle that events in the past occurred suddenly and by different mechanisms than those occurring today. • Each boundary between strata corresponded to a catastrophe (drought, flood, super volcano) destroyed many of the local species. • Area repopulated by immigration.

12. Formation of sedimentary rock and deposition of fossils from different time periods

13. Fathers of Modern GeologyHutton & Lyell 1795 James Hutton, Scottish geologist Explained Earth’s geologic features by the theory of Gradualism: Speciation occurs gradually, profound change is the cumulative product of slow but continuous processes. Charles Lyell (1797-1875) geologist incorporated gradualism into the theory of Uniformitarianism: Geologic processes have not changed throughout Earth’s history (ie. forces that build and erode mountains occur at a steady rate) thus Earth is much older than previously believed.

14. Strata of sedimentary rock at the Grand Canyon

15. IMPORTANT CONCLUSIONS: • Earth must be very old much older than six thousand years (it is 4.5 billion years old) • Very slow and subtle processes persisting over a long period of time can add up to substantial change. • Slow but significant changes in environments caused slow but significant changes in species over “geologic time.” • By the end of the 18th century several naturalists, including Darwin’s grandfather Erasmus Darwin, suggested that life had evolved as environments changed. No one had suggested a mechanism.

16. The Inheritance of Acquired Characteristics Jean Baptiste de Lamarck proposed the first explanation that was widely accepted for years. Three parts: • Use and disuse described how body parts of organisms can develop with increased usage, while unused parts weaken. Correct. • Inheritance of acquired characteristics described how body features acquired during the lifetime of an organism (such as muscle bulk) could be passed on to offspring. Incorrect. • Natural transformation of species described how organisms produced offspring with changes, transforming each generation into a slightly different form that is more complex. Species did not become extinct nor did they split and change into two or more species. Incorrect.

17. The giraffe • Short neck. • Food scarce. • Stretch neck. • Eat. • Have a slightly longer neck. • Have offspring with slightly longer neck. • Repeat. • Inheritance of Acquired Characteristics or Lamarckism

18. Descent with Modification via Natural Selection by DARWIN • Charles Darwin 1809-1882 • Med school dropout • BA Natural Theology • Captain Fitzroy- HMS Beagle - 5 years of travel UNPAID • Galapagos, islands of relatively recent volcanic origin, 900 km west of SA coast. • Gathered mountains of evidence • Waited 20 years to write and publish a groundbreaking book.

19. Alfred Russell Wallace(1823-1913) Presented a paper with identical ideas as Darwin on July 1, 1858 at the Linnaean Society meeting Was a botanist who came up with virtually the same concept of natural selection more or less independently through his studies on the Malay archipelago. Darwin panicked because he was not ready with his book yet!

20. Journey of the H.M.S. Beagle

21. The historical context of Darwin’s life and ideas.

22. Darwin’s Field Research • S.American flora/fauna are distinct from European flora/fauna • S. American temperate species were more closely related to S. American tropical species than European temperate species • S. American fossils were distinctly S. American Tropical Rainforest of South America

23. Darwin’s Field Research • Most animal species on Galapagos unique to those islands, but resemble S. American continental species • Darwin’s Finches • 13 types • some unique to individual island • others found on two or more islands close together • Darwin proposed • new species could arise from an ancestral population by gradually accumulating adaptations to a different environment. • Theory of natural selection as the mechanism of adaptive evolution

24. On the Origin of Species • By Means of Natural Selection November 24, 1859 • Darwins’s groundbreaking book explained what had once seemed a bewildering array of unrelated facts. • He focused on: • Diversity of organisms • Similarities & differences • Geographic distribution • Adaptations to surrounding • environments

25. Main Ideas of Natural Selection • Overproduction of offspring… populations posses an enormous reproductive potential. ex. Darwin calculated that two elephants would produce a population of 19 million individuals after 750 years if all offspring survived to reproductive maturity and fostered their normal number of offspring.

26. Main Ideas of Natural Selection 2) Members of a population compete for survival. • Population sizes remain stable- populations generally fluctuate around a constant size. • Resources are limited. Resources such as food, water, light don’t increase as populations grow larger. • Eventually, the needs of a growing population will exceed the available resources. • As a result, individuals must compete for resources.

27. Main Ideas of Natural Selection 3) Genetic variability exists among individuals in a population. • Most traits reveal considerable variety in their form.

28. Main Ideas of Natural Selection 4) Some individuals will be better suited for their environment. • Only the individuals most fit to their environment survive to breed. • Individuals with traits best adapted for survival in the environment are able to out-compete other individuals for resources.

29. Main Ideas of Natural Selection 5) Individuals with the better adaptations survive and leave offspring who inherit the traits of their parents. • In turn, the best adapted of these offspring leave the most offspring. • Over time, traits best adapted for survival in the environment and the alleles that generate them accumulate in the population. Evolution occurs as advantageous traits accumulate.

30. Key Points of Natural Selection • Populations (groups of interbreeding individuals belonging to a particular species and sharing a common geographic area) are the smallest unit that can evolve. Evolution is measurable over successive generations. • Natural selection acts only onheritable variations/phenotypes. (not acquired ones) • Natural selection is situational as environmental factors vary from place to place and from time to time. An adaptation in one situation may be useless or even detrimental in another situation.

31. Natural selection is differential success in reproductionthat results from the interaction between individuals that vary in heritable traits and their environment

32. Summary • Theory - an accepted hypothesis that has been tested over and over again without yet being disproved • Definition- Evolution is the change in the overall genetic makeup of a population over time • Three Basic Components • Individuals cannot evolve.  Populations evolve. • Natural selection is the mechanism of evolution. • Evolution occurs situationally (NOT GOAL ORIENTED).

33. Artificial Selection • Humans make breeding choices among livestock, crops, dogs, horses, etc.

34. ORGANIZE YOUR THOUGHTS! EVIDENCE FOR EVOLUTION • Direct Observations • The FossilRecord • Homology • Biogeography

35. EVIDENCE FOR EVOLUTION Direct observation • Historical examples that support the theory of natural selection • Pesticide resistance • Antibiotic resistance • HIV • Sickle Cell Anemia- Malaria

36. Evolution of insecticide resistance in insect populations

37. Evolution of drug resistance in HIV

38. EVIDENCE FOR EVOLUTIONThe Fossil Record • Paleontologyprovides fossils that reveal the prehistoric existence of extinct species. As a result, changes in species and the formation of new species can be studied. • Fossil deposits are often among sediment layers. • Law of superposition states that the deepest layer of earth contains the oldest specimens.

39. Fossil Record • The fossilrecord refers to the order in which fossils appear within layers of rock that mark the passing of geologic time.

40. PATTERNS OF EVOLUTION Homology • Comparative anatomydescribes two kinds of structures that contribute to the identification of evolutionary relationships among species. Compares external morphology and internal anatomy • Homologous structures: have different functions and may look different but may resemble one another in different species because they have evolved from a common ancestor. • Divergent Evolution: two or more species originate from a common ancestor.

41. Morphology

42. Homologous structures: anatomical signs of descent with modification

44. EVIDENCE FOR EVOLUTION • Embryology is the study of embryos and their development. • Reveals similar stages in development (ontogeny) among related species. • The similarities help establish evolutionary relationships (phylogeny).

45. Ontogenetic Homology The human embryo has gills, a post-analtail, webbing between the toes & fingers, & spends its entire time floating anddeveloping in amniotic fluid has similar salt concentration as ocean water

46. Pharyngeal pouches Post-anal tail Chick embryo Human embryo Figure 22.15

47. EVIDENCE FOR EVOLUTION • Vestigial organs:organs with no apparent function or purpose imply evolutionary relationships to primitive ancestors. • May still be around as an evolutionary relic. • The structure served a purpose in an ancient ancestor but no longer does. Example: pelvic girdle, hind leg bones in whales

49. A transitional fossil linking past and present