1. CHAPTER 2 The Development of Evolutionary Theory

2. Chapter Outline  Brief History of Evolutionary Thought  Natural Selection  Natural Selection in Action  Constraints on Nineteenth-Century Evolutionary Theory  Opposition to Evolution  Why It Matters

3. Focus Questions  What are the basic premises of natural selection?  What were the technological and philosophical changes that led people to accept notions of evolutionary change?

4. Introduction to the Subject of Evolution  Evolution is the most fundamental of all biological processes, but one of the most misunderstood.  Humans evolved from a species that lived some 6- 8 million years ago (mya), not monkeys or chimpanzees.  Humans do share a recent common ancestor with other primates

5.  Evolution takes time; hence, the appearance of a new species is rarely witnessed (microevolutionary changes occur, however: see Chapt. 1)  The subject of evolution is controversial, especially in the U.S. because of conflicting spiritual teachings

6. Evolution Is a Theory  The theory has been tested and subjected to verification through accumulated evidence (and has not been disproved)  The theory of evolution has been supported by a mounting body of genetic evidence.  The theory has stood the test of time.  The theory continues to grow.

7. A Brief History of Evolutionary Thought  Evolutionary principles were developed in western Europe, made possible by scientific thinking dating to the 16 th century.  Western science, however, borrowed ideas from Arab, Indian, and Chinese cultures where notions of biological evolution had already developed.  By the 19 th century, evolution wasn’t a new concept, but Natural Selection was a new theory

8. Natural Selection  The most critical mechanism of evolutionary change, first explained by Charles Darwin  Same conclusions were independently reached by Alfred Russel Wallace.

9. Barrier to Evolutionary Thought: Fixity of Species  The notion that species, once created, can never change  an idea diametrically opposed to theories of biological evolution.  To challenge the idea was to challenge the Argument from Design (life engineered by a purposeful God).

10. The Scientific Revolution  Came with the discovery of the New World, introducing new ideas and challenging fundamental views about the planet.  Exposure to new plants and animals increased awareness of biological diversity.

11. Challenges to traditional beliefs  Aristotle taught that the sun and planets existed in a series of concentric spheres that revolved around the sun.  Copernicus challenged the idea that the earth was the center of the universe.  Galileo’s work supported the idea that the universe was a place of motion.

12. Aristotle’s View  This seventeenth-century map shows the earth at the center of the solar system.  Ideas generated out of the Scientific Revolution Challenges such long- standing beliefs

13. Precursors to the Theory of Evolution  John Ray, a minister educated at Cambridge University, developed the concept of species.  He recognized that groups of plants and animals could be differentiated from other groups by their ability to mate with one another and produce offspring.  He placed such groups of reproductively isolated organisms into a single category, which he called the species.

14. Precursors to the Theory of Evolution  Carolus Linnaeus, a Swedish naturalist who developed a method of classifying plants and animals.  In Systema Naturae, first published in 1735, he standardized Ray’s use of genus and species terminology and established the system of binomial nomenclature.  He added two more categories: class and order.  Linnaeus’ four-level system became the basis for taxonomy.

15. Precursors to the Theory of Evolution  Erasmus Darwin, Charles Darwin’s grandfather  Physician, poet, and leading member of an intellectual community in England  In a poem, expressed the view that life had originated in the seas and all species descended from a common ancestor.  Charles read his grandfather’s writings, but how much he was influenced by them is unknown.

16. Precursors to the Theory of Evolution  Jean-Baptiste Lamarck developed a theory to explain the evolutionary process, known as the inheritance of acquired characteristics.  An example is the giraffe: having stripped the leaves from the lower branches of a tree, the animal tries to reach leaves on upper branches.  The neck becomes slightly longer.  The longer neck is passed on to offspring.

17. Lamarck’s View of Evolution  Individual changes, transmits that change to offspring

18. Darwin-Wallace View of Evolution  Environment favors individuals with long necks  Those individuals more likely than others to have offspring

19. Georges Cuvier and Catastrophism  An opponent to Lamarck, Cuvier explained the fossil record as the result of a succession of catastrophes followed by new creation events.  The view that the earth’s geological landscape is the result of violent cataclysmic events.

20.  Thomas Malthus, author of an essay that inspired both Charles Darwin and Alfred Wallace in their separate discoveries of natural selection.  Was arguing for limits of human population growth, not concerned with how species change.  The limits for populations to increase is controlled by availability of resources.  The latter was extended to all organisms by Darwin and Wallace.

21. Charlies Lyell  A lawyer, geologist, and, for Charles Darwin’s friend and mentor.  Before meeting Darwin in 1836, Lyell had earned acceptance in Europe’s most prestigious scientific circles, thanks to his praised Principles of Geology, published during the years 1830– 1833.

22. Uniformitarianism  The theory that the earth’s features are the result of long-term natural processes (i.e. wind, water erosion, local flooding, frost, decomposition, volcanoes, earthquakes, and glacial movements) that continue to operate in the present as they did in the past.  Proposed by James Hutton, elaborated on by Lyell, this theory opposed catastrophism and contributed strongly to the concept of immense geological time.

23. These limestone cliffs in southern France were formed around 300 million years ago from shells and the skeletal remains of countless sea creatures.

24. Mary Anning  When her father died, Anning began collecting and selling marine fossils to support her family.  She discovered the first fossilized Pleiosaurus (ocean-dwelling reptile) and became known as one of the world’s leading “fossilists.”

25. Charles Darwin (1809-1882)  Ideas were formed while serving as a naturalist on the 5-year voyage of the HMS Beagle.  Darwin saw the importance of biological variation within a species.  Recognized that sexual reproduction increased variation, but did not yet know why.

26. The Route of the HMS Beagle

27. The Struggle for Existence  The idea that in each generation more offspring are born than survive to adulthood, coupled with the notions of competition for resources and biological diversity led to the theory of evolution.  He wrote,“ It at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed.”

28. Beak Variation in Darwin’s Galápagos Finches Ground finch  Main food: seeds  Beak: heavy

29. Beak Variation in Darwin’s Galápagos Finches Tree finch  Main food: leaves, buds, blossoms, fruits  Beak: thick, short

30. Beak Variation in Darwin’s Galápagos Finches Tree finch (called woodpecker finch)  Main food: insects  Beak: stout, straight

31. Beak Variation in Darwin’s Galápagos Finches Ground finch (known as warbler finch)  Main food: insects  Beak: slender

32. Domestic Dogs  All domestic dogs share a common ancestor, the wolf. The extreme variation exhibited by dog breeds today has been achieved in a relatively short time through artificial selection.

33. Alfred Russell Wallace (1823-1913)  Suggested species descended from other species and new species were influenced by environmental factors.  Presented joint paper, coauthored with Darwin, on evolution and natural selection to the Linnean Society of London

34. Processes of Natural Selection, are “the key” to understanding evolution  Once Darwin understood how selection occurs in nature, he outlined the processes.

35. Natural Selection, the basic processes 1. All species are capable of producing offspring at a faster rate than food supplies increase. 2. There is biological variation within all species. 3. Since in each generation, more individuals are produced than can survive, and because of limited resources, there is competition (not necessarily the same thing as fighting, however) among individuals.

36. Processes of Natural Selection 4. Individuals possessing favorable variations or traits (i.e. speed, resistance to disease, protective coloration) have an advantage over those who do not. In other words, have greater fitness because favorable traits increase the likelihood of survival and reproduction.

37. 5. The environmental context determines whether or not a trait is beneficial. Hence, favorable traits become most advantageous are the results of a natural process. 6. Traits are inherited and passed on to the next generation. Individuals who produce more offspring are said to have a greater reproductive success, or fitness.

38. Processes of Natural Selection 7. Variations accumulate over long periods of time, so later generations may be distinct from ancestral ones. 8. As populations respond to pressures over time, they may become distinct species, descended from a common ancestor.

39.  Over long periods of geological time, successful variations accumulate in a population  Later generations may be distinct from ancestral ones, or a new species can appear.

40.  Geographical isolation (distance, natural barriers such as oceans) contributes to the formation of new species as individuals begin to adapt to different environments.  Selective pressures (differential ecological circumstances) cause distinct species to develop. See, for example, the 13 species of Galápagos finches presumably all descended from a common South American ancestor.

41. Evolutionary Change Through Natural Selection 1. A trait must be inherited if natural selection is to act on it. 2. Natural selection can’t occur without population variation in inherited characteristics. 3. Fitness is a relative measure that changes as the environment changes. 4. Natural selection can only act on traits that affect reproduction.

42. Fitness  Pertaining to natural selection, a measure of relative reproductive success of individuals.  Fitness can be measured by an individual’s genetic contribution to the next generation compared to that of other individuals.

43. Fertility  The ability to conceive and produce healthy offspring.  An animal that gives birth to more young passes its genes on a faster rate than one that bears few offspring.  An important element, however, is also the number of young raised successfully to the point where they reproduce, or differential net reproductive success.

44. Genome  With the discovery of the structure of DNA came the understanding of the entire genetic makeup of an individual or species.  Human and chimpanzee genomes were sequenced in 2003 and 2005, respectively.

45. Biological Continuity  Refers to a biological continuum.  When expressions of a phenomenon continuously grade into one another so that there are no discrete categories, they exist on a continuum.  Color is one such phenomenon, and life-forms are another.  Most people hold to belief systems that do not emphasize this or offer scientific explanations.

46. Religion and Science  Religion and science concern different aspects of the human experience, and they are not inherently mutually exclusive categories.  Belief in God does not exclude the possibility of biological evolution; acknowledgement of evolutionary processes doesn’t preclude the existence of God.  Evolutionary theories are not rejected by all religions or by most forms of Christianity.

47. Scopes Monkey Trial Clarence Darrow sitting on the edge of the table; John Scopes sitting with arms folded behind Darrow

48. Christian Fundamentalists  Conservative Christians (“Creationists”) seeking a revival of “traditional values” and banning any theory that does not support the biblical version of the creation of humankind.  Adherents to a movement in American Protestantism that began in the early twentieth century.  This group holds that the teachings of the Bible are infallible and are to be taken literally.

49. Creation Science, Intelligent Design  Argue that creation science and intelligent design (ID) is as much a scientific endeavor as is evolution, and suggest scientific evidence to support creationist views  ID is not science, however  Creationists argue their view is absolute and fallible, which is counter to science which seeks testable hypotheses

50. Why It Matters  One of the greatest controversies regarding education in the United States and other parts of the world is the teaching of evolution.

51. Example: HINI Flu viruses are the result of viruses “evolving” or changing in form.  Medical researchers try to predict which of several strains will pose the most serious threat and try to develop a vaccine that targets that specific “evolving” strain.  If future physicians and researchers don’t understand evolution, there is little hope they can forestall potential medical crises as the pace of change in pathogens exceeds that of the antibiotics designed to defeat them.

52. Contemporary Health Challenges  The inevitable outcome of our more aggressive methods to fight microbes (disease causing micro- organisms such as bacteria and viruses) will lead to modified micro-organisms that have evolved to resist therapies such as antibiotics. More use of antibiotics to treat bacterial infections weed out vulnerable microbes, but leave less vulnerable to reproduce. Less vulnerable cause more serious forms of disease than the organisms that were eliminated.

53. QUICK QUIZ

54. 1. To understand the complexities of evolution one must be well versed in a) mathematics and statistics. b) botany and paleontology. c) genetics and biology. d) anatomy and physiology.

55. Answer: c  To understand the complexities of evolution one must be well versed in genetics and biology.

56. 2. Genetic evidence supports evolution. a) True b) False

57. Answer: true  Genetic evidence supports evolution

58. 3. Darwin realized that variation among _________________ was how selection occurred, ultimately causing change in species.

59. Answer: individuals Darwin realized that variation among individuals was how selection occurred, ultimately causing change in species

60. 5. Natural selection acts on existing _________________ within a species.

61. Answer: variation  Natural selection acts on existing variation within a species.