Darwin and Evolution Chapter 17

Darwin and Evolution 2Outline History of Evolutionary Thought Darwin’s Theory of Evolution  Earth very old  Descend with change from a common ancestor  Adaptation to a changing environment The Evidence of Evolution  Fossil  Biogeographical  Anatomical  Biochemical

3 Voyage of the HMS Beagle

4 Charles Darwin at 31

Darwin and Evolution 5 History of Evolutionary Thought Prior to Darwin  View of nature determined by deep-seated beliefs  Held to be intractable truths  Biology thought had slowly begun to accept ­Various ideas of evolution ­Similarities between living things reflect recent common ancestry ­Dissimilarities between living things reflect ancient common ancestry

6 Evolutionary Thought before Darwin

Darwin and Evolution 7 Mid-Eighteenth Century Taxonomy matured during mid-eighteenth century  Linnaeus believed in: ­The fixity of species ­That each species had:  An ideal structure and function, and  A place in the scala naturae (scale of complexity)  Count Buffon: ­Wrote 44-volume catalog of all known plants and animals ­Suggested descent with modification

Darwin and Evolution 8 Late Eighteenth Century Cuvier:  First to use comparative anatomy to develop a system of classification  Founded Paleontology  Proposed Catastrophism ­Local catastrophes in past had caused later strata to have a new mix of fossils ­After each catastrophe, the region was repopulated by species from surrounding areas

Darwin and Evolution 9 Late Eighteenth Century Lamarck:  First biologist to: ­Propose evolution ­Link diversity with environmental adaptation  Concluded more complex organisms are descended from less complex organisms  Proposed inheritance of acquired characteristics – Lamarckianism Charles Lyell:  Earth is subject to slow but continuous cycles of erosion and uplift  Proposed uniformitarianism, rates and processes of change are constant

10 Formation of Sedimentary Rock

Darwin and Evolution 11 Darwin’s Theory of Evolution Geological observations consistent with those of Hutton & Lyell Biogeographical observations:  The study of the geographic distribution of life forms on earth  Darwin saw similar species in similar habitats;  Reasoned related species could be modified according to the environment

12 A Glyptodont and a Giant Sloth

13 The Patagonian Hare, Dolichotis patagonium

Darwin and Evolution 14 Galápagos Islands Tortoises  Darwin observed tortoise neck length varied from island to island  Proposed that speciation on islands correlated with a difference in vegetation Finches  Darwin observed many different species of finches on various islands  Speculated they could have descended from a single pair of mainland finch

15 Galápagos Tortoises, Geochelone

16 Galápagos Finches

Darwin and Evolution 17 Natural Selection and Adaptation Individuals have heritable variations More individuals produced each generation than environment can support Some individuals have adaptive characteristics  Enables increased survival and reproduction  Increasing proportion of succeeding generations will have these characteristics Populations become adapted to their local environment through change in individuals

18 Variation in a Population

Darwin and Evolution 19 Organisms Have Variations Darwin emphasized that individuals from a population vary in their:  Functional characteristics  Physical characteristics  Behavioral characteristics Proposed that these variations:  Are essential  Allow adaptation to the environment over time

20 Artificial Selection of Animals

21 Artificial Selection of Plants

Darwin and Evolution 22 Organisms Struggle to Exist Malthus  Each generation has the same reproductive potential as the previous generation ­Reproductive potential is greater than environment can support ­Death, disease, and famine were inevitable if population were to have stability  Individuals experience a constant struggle for survival

Darwin and Evolution 23 Organisms Differ in Fitness Fitness is the relative reproductive success of an individual  The most-fit individuals in a population capture a disproportionate share of goodies  Interactions with the environment determine which individuals reproduce the most Adaptation  Changes that help a species become more suited to its environment  Product of natural selection

24 Transitional Fossils

Darwin and Evolution 25 The Evidence of Evolution: Anatomical Vertebrate forelimbs:  Homologous - All contain the same sets of bones in similar ways  Yet they are modified extensively to meet various adaptive needs  Darwin interpreted this as support for a hypothesis of common descent Embryological development  All vertebrate embryos have:  A postanal tail and  Paired pharyngeal (gill) pouches

26 Biogeography

Darwin and Evolution 27 The Evidence of Evolution: Anatomical Homologous Structures:  Anatomically similar because they are inherited from a common ancestor  May be functionally similar or not Analogous Structures:  Serve the same function  Not constructed similarly  Do not share a common ancestor Vestigal Structures:  Fully-developed anatomical structures  Reduced or obsolete function

28 Significance of Homologous Structures

29 Significance of Developmental Similarities

30 Vestigial Limbs in Whales

Darwin and Evolution 31 The Evidence of Evolution: Fossil & Biogeographical Fossil Evidence  Fossils record the history of life from the past  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 Biogeographical  Distributions of plants and animals across earth  Consistent with origin in one locale and then spread to accessible regions

Darwin and Evolution 32 Biochemical Evidence Almost all living organisms:  Use the same basic biochemical molecules  Utilize same DNA triplet code  Utilize same 20 amino acids in their proteins DNA base-sequence differences:  When very similar, suggest recent common descent  When more different, suggest more ancient common descent

33 Significance of Biochemical Differences

Darwin and Evolution 34Review History of Evolutionary Thought Darwin’s Theory of Evolution  Earth very old  Descend with change from a common ancestor  Adaptation to a changing environment The Evidence of Evolution  Fossil  Biogeographical  Anatomical  Biochemical

Darwin and Evolution Ending Slide Chapter 17