Natural Selection A Summary Individuals with certain heritable
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 Video: Seahorse Camouflage Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -12 (a) A flower mantid in Malaysia (b) A stick mantid in Africa
• Note that individuals do not evolve; populations evolve over time • Natural selection can only increase or decrease heritable traits in a population • Adaptations vary with different environments Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Concept 22. 3: Evolution is supported by an overwhelming amount of scientific evidence • New discoveries continue to fill the gaps identified by Darwin in The Origin of Species Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
EXPERIMENT Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” RESULTS 12 12 Number of colored spots Area of colored spots (mm 2) Fig. 22 -13 10 8 6 4 2 0 Source population Transplanted population
• 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 3 TC • The ability of bacteria and viruses to evolve rapidly poses a challenge to our society Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Percent of HIV resistant to 3 TC Fig. 22 -14 100 Patient No. 1 Patient No. 2 75 50 Patient No. 3 25 0 0 2 4 6 Weeks 8 10 12
• 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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
The Fossil Record • The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -15 c 0 4 3 Depth (meters) 2 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10
• 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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -16 (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)
Homology • Homology is similarity resulting from common ancestry Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Anatomical and Molecular Homologies • Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -17 Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat
• Comparative embryology reveals anatomical homologies not visible in adult organisms Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -18 Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo
• Vestigial structures are remnants of features that served important functions in the organism’s ancestors • Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Homologies and “Tree Thinking” • The Darwinian concept of an evolutionary tree of life can explain homologies • Evolutionary trees are hypotheses about the relationships among different groups • Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -19 Branch point (common ancestor) Lungfishes Amnion Lizards and snakes 3 4 Homologous characteristic Amniotes Tetrapod limbs Mammals 2 Crocodiles Ostriches 6 Feathers Hawks and other birds Birds 5 Tetrapods Amphibians 1
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 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
Fig. 22 -20 Sugar glider NORTH AMERICA AUSTRALIA Flying squirrel
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 integrates diverse areas of biological study and stimulates many new research questions • Ongoing research adds to our understanding of evolution Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
You should now be able to: 1. Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace 2. Describe Lamarck’s theories, and explain why they have been rejected 3. Explain what Darwin meant by “descent with modification” 4. List and explain Darwin’s four observations and two inferences Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
5. Explain why an individual organism cannot evolve 6. Describe at least four lines of evidence for evolution by natural selection Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings
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