1. Chapter 22 Darwin and Evolution Chapter 22 Darwin and Evolution

2. Charles Darwin Charles Darwin (1809-1882) is credited with proposing that the mechanism for the process of evolution is natural selection. Charles Darwin (1809-1882) is credited with proposing that the mechanism for the process of evolution is natural selection. Darwin spent five years on a voyage that took him around the world with the majority of his time spent in South America and its neighboring islands. Darwin spent five years on a voyage that took him around the world with the majority of his time spent in South America and its neighboring islands. Darwin published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species. Darwin published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species. 2

3. Charles Darwin He established that all species of life have descended over time from common ancestors, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding. 3

4. Charles Darwin By the 1870s the scientific community and much of the general public had accepted evolution as a fact. By the 1870s the scientific community and much of the general public had accepted evolution as a fact. However, many favored competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution. However, many favored competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life. 4

5. Evolution Evolution:the change over time of the genetic composition of populations Evolution:the change over time of the genetic composition of populations Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) Natural selection: populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success) Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction Evolutionary adaptations: a prevalence of inherited characteristics that enhance organisms’ survival and reproduction November 24, 1859

6. History of Evolutionary Thought Mid-Eighteenth Century Influences: Mid-Eighteenth Century Influences: Taxonomy matured during the mid-eighteenth century Taxonomy matured during the mid-eighteenth century Linnaeus believed in the fixity of species Linnaeus believed in the fixity of species Each species had: Each species had: An ideal structure and function, and An ideal structure and function, and A place in the scala naturae (a sequential ladder of life) A place in the scala naturae (a sequential ladder of life) He developed the binomial system of nomenclature He developed the binomial system of nomenclature System of classification for living things System of classification for living things Count Buffon: Count Buffon: A French naturalist A French naturalist Wrote a 44-volume catalog of all known plants and animals Wrote a 44-volume catalog of all known plants and animals Provided evidence of descent with modification Provided evidence of descent with modification Suggested mechanisms including environmental influences, migration, geographic isolation, and the struggle for existence Suggested mechanisms including environmental influences, migration, geographic isolation, and the struggle for existence 6

7. History of Evolutionary Thought Late Eighteenth Century Influences: Late Eighteenth Century Influences: Cuvier: Cuvier: First to use comparative anatomy to develop a system of classifying animals First to use comparative anatomy to develop a system of classifying animals Founded the science of paleontology Founded the science of paleontology Proposed catastrophism Proposed catastrophism Local catastrophes in the past had caused the Earth’s strata to have a new mix of fossils Local catastrophes in the past had caused the Earth’s strata to have a new mix of fossils After each catastrophe, the region was repopulated by species from surrounding areas After each catastrophe, the region was repopulated by species from surrounding areas The result of the catastrophes was change appearing over time The result of the catastrophes was change appearing over time 7

8. History of Evolutionary Thought Late Eighteenth Century Influences: Late Eighteenth Century Influences: Lamarck: Lamarck: First biologist to: First biologist to: Propose evolution Propose evolution Link diversity with environmental adaptation Link diversity with environmental adaptation Concluded that more complex organisms are descended from less complex organisms Concluded that more complex organisms are descended from less complex organisms Proposed the inheritance of acquired characteristics – Lamarckianism Proposed the inheritance of acquired characteristics – Lamarckianism Charles Lyell: Charles Lyell: Earth is subject to slow but continuous cycles of erosion and uplift Earth is subject to slow but continuous cycles of erosion and uplift Proposed uniformitarianism, which states that rates and processes of change are constant Proposed uniformitarianism, which states that rates and processes of change are constant 8

9. Darwin’s Theory of Evolution Geological observations consistent with those of Hutton & Lyell Geological observations consistent with those of Hutton & Lyell Biogeography: Biogeography: The study of the geographic distribution of life forms on earth The study of the geographic distribution of life forms on earth Darwin saw similar species in similar habitats Darwin saw similar species in similar habitats Reasoned that related species could be modified according to the environment Reasoned that related species could be modified according to the environment Living forms could be descended from extinct forms known only from the fossil record Living forms could be descended from extinct forms known only from the fossil record 9

10. Darwin’s Theory of Evolution Galapagos Islands Galapagos Islands Tortoises Tortoises Darwin observed that tortoise neck length varied from island to island Darwin observed that tortoise neck length varied from island to island Proposed that speciation on islands correlated with a difference in vegetation Proposed that speciation on islands correlated with a difference in vegetation Finches Finches Darwin observed many different species of finches on various islands Darwin observed many different species of finches on various islands Significant variety in beaks Significant variety in beaks Speculated that they could have descended from a type of mainland finches Speculated that they could have descended from a type of mainland finches 10

11. Galápagos Tortoises 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a.b. a: © Kevin Schafer/Corbis; b: © Michael Dick/Animals Animals/Earth Scenes

12. Darwin’s Theory of Evolution Natural Selection and Adaptation: Natural Selection and Adaptation: Members of a population have inheritable variations Members of a population have inheritable variations More individuals are produced in each generation than environment can support More individuals are produced in each generation than environment can support Some individuals have adaptive characteristics Some individuals have adaptive characteristics Favorable traits that result in increased survival and reproduction Favorable traits that result in increased survival and reproduction Natural selection can result in a population adapted to the local environment Natural selection can result in a population adapted to the local environment An increasing proportion of succeeding generations will have favorable characteristics An increasing proportion of succeeding generations will have favorable characteristics 12

13. Darwin’s Theory of Evolution Darwin emphasized that individuals from a population vary in their: Darwin emphasized that individuals from a population vary in their: Functional characteristics Functional characteristics Physical characteristics Physical characteristics Behavioral characteristics Behavioral characteristics He proposed that these variations: He proposed that these variations: Occur randomly Occur randomly Are essential to the natural selection process Are essential to the natural selection process Allow adaptation to the environment over time Allow adaptation to the environment over time 13

14. Darwin’s Theory of Evolution Fitness is the relative reproductive success of an individual Fitness is the relative reproductive success of an individual The most-fit individuals in a population capture a disproportionate share of goodies The most-fit individuals in a population capture a disproportionate share of goodies Interactions with the environment determine which individuals reproduce the most Interactions with the environment determine which individuals reproduce the most Adaptation Adaptation Change that helps a species become more suited to its environment Change that helps a species become more suited to its environment Product of natural selection Product of natural selection 14

15. The Origin of Species Darwin made Two main points: Darwin made Two main points: Species of organisms inhabiting earth today descended from ancestral species Species of organisms inhabiting earth today descended from ancestral species He proposed that the mechanism for evolution was natural selection He proposed that the mechanism for evolution was natural selection Used the term descent with modification until the last paragraph and then called it evolution Used the term descent with modification until the last paragraph and then called it evolution

16. Darwin’s Theory of Evolution Artificial selection Artificial selection A breeder chooses which traits to perpetuate and selects the plants and animals that will reproduce A breeder chooses which traits to perpetuate and selects the plants and animals that will reproduce All dogs are descended from the gray wolf All dogs are descended from the gray wolf Began to be domesticated about 14,000 years ago. Began to be domesticated about 14,000 years ago. The process of diversification led to extreme phenotypic differences The process of diversification led to extreme phenotypic differences The wolves under domestication were separated from other wolves. The wolves under domestication were separated from other wolves. Each human tribe selected for whatever traits appealed to them. Each human tribe selected for whatever traits appealed to them. 16

17. Artificial Selection of Animals 17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Boston terrier Irish wolfhound Wolf Left: © Gary Milburn/Tom Stack & Assoc.; Top right: © Robert Dowling/Corbis; Bottom right:© Ralph Reinhold/Index Stock Imagery/Photolibrary RF ;

18. Darwin’s Theory of Evolution 18 Each of the 13 species of Galápagos finches has a beak adapted to a particular way of life.  A heavy beak is suited to a diet of large seeds  The beak of the warbler-finch is suited to feeding on insects  A longer, somewhat decurved beak and the split tongue of the cactus-finch are suited to probing a cactus for seeds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. Large, ground-dwelling finchb. Warbler-finchc. Cactus-finch a: © Adrienne T. Gibson/Animals Animals/Earth Scenes; b: © Joe McDonald/Animals Animals/Earth Scenes; c: © Leonard Lee Rue/Animals Animals/Earth Scenes;

19. 19 Darwin’s Theory of Evolution Peter and Rosemary Grant are observing natural selection as it occurs in finches on Daphne Major  The beak size of the medium ground finch adapts to the weather Other observations of natural selection  Changes in the shells of marine snails due to hunting by crabs  Changes in the beak length of the scarlet honeycreeper due to a new food source  Industrial melanism  Bacterial resistance to antibiotics

20. Evolution in Action 20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. dry year medium ground finch wet year 1984198219801977 Beak Depth

21. Evidence for Evolution Fossil evidence Fossil evidence Fossils are the remains and traces of past life or any other direct evidence of past life such as trails, footprints, or preserved droppings Fossils are the remains and traces of past life or any other direct evidence of past life such as trails, footprints, or preserved droppings Fossils record the history of life from the past Fossils record the history of life from the past Document a succession of life forms from the simple to the more complex Document a succession of life forms from the simple to the more complex Sometimes the fossil record is complete enough to show descent from an ancestor Sometimes the fossil record is complete enough to show descent from an ancestor Transitional fossils are a common ancestor for two different groups of organisms Transitional fossils are a common ancestor for two different groups of organisms They allow us to trace the descent of organisms They allow us to trace the descent of organisms 21

22. Evidence for Evolution Biogeographical Evidence: Biogeographical Evidence: Biogeography is the study of the range and distribution of plants and animals throughout the world Biogeography is the study of the range and distribution of plants and animals throughout the world Biogeographical distributions are consistent with the hypothesis that related forms of life evolved in one locale and then spread to accessible regions Biogeographical distributions are consistent with the hypothesis that related forms of life evolved in one locale and then spread to accessible regions A different mix of plants and animals would be expected whenever geography separates continents, islands, seas, etc. A different mix of plants and animals would be expected whenever geography separates continents, islands, seas, etc. 22

23. Evidence for Evolution Anatomical Evidence: Anatomical Evidence: Vertebrate forelimbs: Vertebrate forelimbs: Homologous structures - All contain the same sets of organized bones in similar ways Homologous structures - All contain the same sets of organized bones in similar ways Yet they are modified extensively to meet various adaptive needs Yet they are modified extensively to meet various adaptive needs Darwin interpreted this as support for a hypothesis of common descent Darwin interpreted this as support for a hypothesis of common descent Embryological development Embryological development All vertebrate embryos have: All vertebrate embryos have: A postanal tail and A postanal tail and Paired pharyngeal (gill) pouches Paired pharyngeal (gill) pouches 23

24. The Evidence of Evolution Homologous Structures: Homologous Structures: Anatomically similar because they are inherited from a common ancestor Anatomically similar because they are inherited from a common ancestor May be functionally similar or not May be functionally similar or not Analogous Structures: Analogous Structures: Serve the same function Serve the same function Are not constructed similarly Are not constructed similarly Do not share a common ancestor Do not share a common ancestor Vestigial Structures: Vestigial Structures: Fully-developed anatomical structures in one group of organisms Fully-developed anatomical structures in one group of organisms Reduced or obsolete function in similar groups Reduced or obsolete function in similar groups 24

25. Significance of Homologous Structures 25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. humanhorsewhalecat bird bat humerus ulna radius metacarpals phalanges

26. Significance of Developmental Similarities 26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. fish salamander tortoise chick human pharyngeal pouches postanal tail

28. Evidence for Evolution Biochemical Evidence: Biochemical Evidence: All living organisms: All living organisms: Use the same basic biochemical molecules Use the same basic biochemical molecules Utilize same DNA triplet code Utilize same DNA triplet code Utilize same 20 amino acids in their proteins Utilize same 20 amino acids in their proteins DNA base-sequence differences: DNA base-sequence differences: When very similar, suggest recent common descent When very similar, suggest recent common descent When more different, suggest more ancient common descent When more different, suggest more ancient common descent 28

29. Significance of Biochemical Differences 29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Number of Amino Acid Differences Compared to Human Cytochrome c yeastmothfishturtleduckpigmonkey human Cytochrome c is a small protein that plays an important role in the electron transport chain within mitochondria of all cells. 0 10 20 30 40 50