1859 Charles Darwin published The Origin of Species IT WAS REVOLUTIONARY! Explained the great diversity of organisms EVOLUTION BY NATURAL SELECTION

Transcription

1 CH Charles Darwin published The Origin of Species IT WAS REVOLUTIONARY! Explained the great diversity of organisms EVOLUTION BY NATURAL SELECTION NATURAL SELECTION IS THE MECHANISM BY WHICH LIVING THINGS EVOLVE

2 Darwin noted current species are descendants of ancestral species Evolution can be defined by Darwin s phrase descent with modification At this time very little was know about genetics at the cellular level and essential nothing was known at the molecular level EVEN SO Darwin was able to gather a massive amount of supporting evidence.

3 WHAT MOST EUROPEANS BELIEVED Species are fixed do not change Old Testament says species were individually designed by God and therefore perfect Earth is very young - ~6000 years old

4 Lamarck s Hypothesis of Evolution Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics The mechanisms he proposed are unsupported by evidence However he did think that species evolved and recognized that each species is adapted to its environment

5 Darwin s Focus on Adaptation In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes From studies made years after Darwin s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches

6 Fig (a) Cactus-eater (c) Seed-eater (b) Insect-eater

7 The Origin of Species Darwin developed two main ideas: Descent with modification explains life s unity and diversity Natural selection is a cause of adaptive evolution

8 Descent with Modification Darwin never used the word evolution in the first edition of The Origin of Species The phrase descent with modification summarized Darwin s perception of the unity of life refers to view that all organisms are related through descent from an ancestor that lived in the remote past

9 In the Darwinian view, the history of life is like a tree with branches representing life s diversity

10 Fig. 22-7

11 Fig Hyracoidea (Hyraxes) Moeritherium Sirenia (Manatees and relatives) Barytherium Deinotherium Mammut Platybelodon Stegodon Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) Millions of years ago Years ago

12 Fig. 22-8a Platybelodon Stegodon Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) Millions of years ago Years ago

13 Artificial Selection, Natural Selection, and Adaptation Darwin noted humans have modified other species by selecting and breeding individuals with desired traits - artificial selection Darwin then described four observations of nature and from these drew two inferences

14 Fig Terminal bud Lateral buds Cabbage Flower clusters Brussels sprouts Leaves Cauliflower Kale Stem Broccoli Wild mustard Flowers and stems Kohlrabi

15 Observation #1: Members of a population often vary greatly in their traits

16 Fig

17 Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support

18 Fig Spore cloud

19 Observation #4: Owing to lack of food or other resources, many of these offspring do not survive

20 Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

21 Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

22 If some heritable traits are advantageous, these will accumulate in the population, and this will increase the frequency of individuals with adaptations This process explains the match between organisms and their environment

23 Natural Selection: A Summary Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals Natural selection increases the adaptation of organisms to their environment over time If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

24 Note that individuals do not evolve; populations evolve over time Natural selection can only increase or decrease heritable traits in a population; IT CANNOT CREATE TRAITS IT MERELY SORTS Adaptations vary with different environments

25 EVIDENCE: Direct Observations of Evolutionary Change Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drugresistant HIV

26 Predation and Coloration in Guppies : Scientific Inquiry John Endler has studied the effects of predators on wild guppy populations Brightly colored males are more attractive to females However, brightly colored males are more vulnerable to predation Guppy populations in pools with fewer predators had more brightly colored males

27 Endler transferred brightly colored guppies (with few predators) to a pool with many predators As predicted, over time the population became less brightly colored Endler also transferred drab colored guppies (with many predators) to a pool with few predators As predicted, over time the population became more brightly colored

28 Number of colored spots Fig EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Guppies: Adult males have brighter colors than those in pike-cichlid pools Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in killifish pools RESULTS Source Transplanted population population 8 2 Source population Transplanted population

29 The Evolution of Drug-Resistant HIV The use of drugs to combat HIV selects for viruses resistant to these drugs HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus

30 Some individual HIV viruses have a variation that allows them to produce DNA without errors These viruses have a greater reproductive success and increase in number relative to the susceptible viruses The population of HIV viruses has therefore developed resistance to 3TC The ability of bacteria and viruses to evolve rapidly poses a challenge to our society

31 Natural selection does not create new traits, but edits or selects for traits already present in the population The local environment determines which traits will be selected for or selected against in any specific population

32 EVIDENCE: The Fossil Record The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

33 Fig Bristolia insolens 8 3 Bristolia bristolensis Bristolia harringtoni Bristolia mohavensis Latham Shale dig site, San Bernardino County, California

34 The Darwinian view of life predicts that evolutionary transitions should leave signs in the fossil record Paleontologists have discovered fossils of many such transitional forms

35 Fig (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

36 EVIDENCE: Homology Homology - similarity resulting from common ancestry Homology is evident at many levels: anatomy, embryos, molecules Evolution is the process of descent with modification Natural selection alters characteristics of ancestral organisms as they face different environments

37 Fig REMODELING OF TETRAPOD FORELIMB homologous structures Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

38 EMBRYOLOGY all vertebrate embryos have post anal tail and pharyngeal (throat) pouches Fig Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo

39 Vestigial structures are remnants of features that served important functions in organism s ancestors; ex. appendix (cecum), coccyx (tail bone) Homology also observed at molecular level similarities in DNA and protein

40 Homologies and Tree Thinking Darwin s evolutionary tree of life can explain homologies Evolutionary trees are hypotheses about relationships among different groups Evidence from variety of data, ex. anatomical and DNA sequence data

41 EVOLUTIONARY TREE FOR TETRAPODS AND THEIR CLOSEST RELATIVES. Fig Branch point (common ancestor) Lungfishes 1 Amphibians Tetrapod limbs 2 Mammals Amnion 3 Lizards and snakes Homologous characteristic 4 5 Feathers 6 Crocodiles Ostriches Hawks and other birds Birds

42 Fig Branch point (common ancestor) ARE CROCODILES MORE CLOSELY RELATED TO LIZARDS Lungfishes OR TO BIRDS? EXPLAIN. 1 Amphibians Tetrapod limbs 2 Mammals Amnion 3 Lizards and snakes Homologous characteristic 4 5 Feathers 6 Crocodiles Ostriches Hawks and other birds Birds

43 Convergent Evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry

44 Fig Sugar glider NORTH AMERICA AUSTRALIA MARSUPIAL PLACENTAL Flying squirrel

45 EVIDENCE: Biogeography Biogeography - geographic distribution of species Influenced by many factors, ex. continental drift, land bridges that open and close as sea levels rise and fall Where did horses originate?

46 EVIDENCE: Biogeography Islands have many endemic species Endemic means found nowhere else Colonized by species from nearest mainland Gave rise new species as they adapt to the new environment

47 What Is Theoretical About Darwin s View of Life? In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena Darwin s theory of evolution by natural selection Has been/continues to be tested Makes sense of a massive amount of data Integrates diverse areas of biological study Continues to generate many new research questions

48 Fig. 22-UN1 Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population.

49 Fig. 22-UN2 Can you explain this data using the theory of evolution by natural selection?

50 INDIVIDUALS DO NOT EVOLVE - populations are the smallest unit of evolution EVOLUTION IS NOT GOAL ORIENTED - there is no need to adapt - differential survival and reproduction leads to change in alleles(genes) of a population

51 Individuals who survive and produce the largest number of fertile offspring are MOST FIT In biology FITNESS is measured in terms of number of offspring produced and whether those offspring survive and produce more offspring