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Descent with Modification: A Darwinian View of Life
Chapter 22 Descent with Modification: A Darwinian View of Life
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Overview: Endless Forms Most Beautiful
A new era of biology began in 1859 when Charles Darwin published The Origin of Species The Origin of Species focused biologists’ attention on the great diversity of organisms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Darwin noted that current species are descendants of ancestral species
Evolution can be defined by Darwin’s phrase descent with modification Evolution can be viewed as both a pattern and a process Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 22-1 Figure 22.1 How can this beetle survive in the desert, and what is it doing?
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Concept 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species To understand why Darwin’s ideas were revolutionary, we must examine them in relation to other Western ideas about Earth and its life Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 22-2 Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) American Revolution French Revolution U.S. Civil War 1750 1800 1850 1900 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his hypothesis of evolution. 1830 Lyell publishes Principles of Geology. Figure 22.2 The historical context of Darwin’s life and ideas 1831–1836 Darwin travels around the world on HMS Beagle. 1837 1837 Darwin begins his notebooks. 1844 Darwin writes essay on descent with modification. 1858 Wallace sends his hypothesis to Darwin. 1859 The Origin of Species is published.
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Scala Naturae and Classification of Species
The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae The Old Testament holds that species were individually designed by God and therefore perfect Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Ideas About Change over Time
The study of fossils helped to lay the groundwork for Darwin’s ideas Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata Video: Grand Canyon Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Layers of deposited sediment Younger stratum with more recent fossils
Fig. 22-3 Layers of deposited sediment Younger stratum with more recent fossils Figure 22.3 Formation of sedimentary strata with fossils Older stratum with older fossils
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Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier
Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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This view strongly influenced Darwin’s thinking
Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time This view strongly influenced Darwin’s thinking Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 22-4 Figure 22.4 Acquired traits cannot be inherited
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Concept 22.2: Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life As the 19th century dawned, it was generally believed that species had remained unchanged since their creation However, a few doubts about the permanence of species were beginning to arise Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Darwin’s Research As a boy and into adulthood, Charles Darwin had a consuming interest in nature Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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The Voyage of the Beagle
During his travels on the Beagle, Darwin collected specimens of South American plants and animals He observed adaptations of plants and animals that inhabited many diverse environments Darwin was influenced by Lyell’s Principles of Geology and thought that the earth was more than 6000 years old Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 22-5 Figure 22.5 The voyage of HMS Beagle
GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA Pinta Genovesa Marchena Equator SOUTH AMERICA Santiago Daphne Islands Pinzón AUSTRALIA Fernandina PACIFIC OCEAN Isabela Figure 22.5 The voyage of HMS Beagle For the Discovery Video Charles Darwin, go to Animation and Video Files. Santa Cruz Andes Cape of Good Hope Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego
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Fig. 22-5a Figure 22.5 The voyage of HMS Beagle Darwin in 1840
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The Galápagos Islands Pinta Genovesa Marchena Santiago Daphne Islands
Fig. 22-5b The Galápagos Islands Pinta Genovesa Marchena Santiago Daphne Islands Pinzón Fernandina Isabela Santa Cruz Santa Fe Figure 22.5 The voyage of HMS Beagle San Cristobal Florenza Española
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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(a) Cactus-eater (c) Seed-eater (b) Insect-eater Fig. 22-6
Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater
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(a) Cactus-eater Fig. 22-6a
Figure 22.6 Beak variation in Galápagos finches (a) Cactus-eater
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(b) Insect-eater Fig. 22-6b
Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater
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Fig. 22-6c Figure 22.6 Beak variation in Galápagos finches (c) Seed-eater
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In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s Darwin quickly finished The Origin of Species and published it the next year Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Darwin’s theory meshed well with the hierarchy of Linnaeus
In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Darwin’s theory meshed well with the hierarchy of Linnaeus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig. 22-7 Figure 22.7 “I think . . .”
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Fig. 22-8 Figure 22.8 Descent with modification Millions of years ago
Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Moeritherium Barytherium Deinotherium Mammut Platybelodon Stegodon Mammuthus Figure 22.8 Descent with modification Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 34 24 5.5 2 104 Millions of years ago Years ago
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34 24 5.5 2 104 Millions of years ago Years ago Fig. 22-8a
Platybelodon Stegodon Mammuthus Elephas maximus (Asia) Loxodonta africana (Africa) Figure 22.8 Descent with modification Loxodonta cyclotis (Africa) 34 24 5.5 2 104 Millions of years ago Years ago
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Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection Darwin then described four observations of nature and from these drew two inferences Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters
Fig. 22-9 Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters Leaves Kale Cauliflower Figure 22.9 Artificial selection Stem Wild mustard Flowers and stems Broccoli Kohlrabi
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Observation #1: Members of a population often vary greatly in their traits
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Fig Figure Variation in a population
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Observation #2: Traits are inherited from parents to offspring
Observation #3: All species are capable of producing more offspring than the environment can support Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig Spore cloud Figure Overproduction of offspring
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Observation #4: Owing to lack of food or other resources, many of these offspring do not survive
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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
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(a) A flower mantid in Malaysia Fig. 22-12a
Figure Camouflage as an example of evolutionary adaptation (a) A flower mantid in Malaysia
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(b) A stick mantid in Africa Fig. 22-12b
Figure Camouflage as an example of evolutionary adaptation (b) A stick mantid in Africa
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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
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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
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Direct Observations of Evolutionary Change
Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug-resistant HIV Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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
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Fig. 22-13 EXPERIMENT RESULTS 12 12 10 10 8 8 Area of colored
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 Figure Can predation result in natural selection for color patterns in guppies? 10 10 8 8 Area of colored spots (mm2) colored spots Number of 6 6 4 4 2 2 Source population Transplanted population Source population Transplanted population
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EXPERIMENT Experimental transplant of guppies Fig. 22-13a
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” Figure Can predation result in natural selection for color patterns in guppies? Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools”
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Area of colored spots (mm2) colored spots Number of
Fig b RESULTS 12 12 10 10 8 8 Area of colored spots (mm2) colored spots Number of 6 6 4 4 2 2 Figure Can predation result in natural selection for color patterns in guppies? Source population Transplanted population Source population Transplanted population
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As predicted, over time the population became less brightly colored
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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fig 100 Patient No. 1 Patient No. 2 75 Percent of HIV resistant to 3TC 50 Patient No. 3 Figure Evolution of drug resistance in HIV 25 2 4 6 8 10 12 Weeks
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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
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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
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Fig. 22-15 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10
2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 12 3 Depth (meters) 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 3 Figure Fossil evidence of evolution in a group of trilobites 2 1 Latham Shale dig site, San Bernardino County, California
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Bristolia harringtoni 14
Fig b 12 Depth (meters) Bristolia harringtoni 2 14 16 18 Bristolia mohavensis 1 2 Figure Fossil evidence of evolution in a group of trilobites Latham Shale dig site, San Bernardino County, California 1
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2 4 6 Depth (meters) 4 Bristolia insolens 4 8 Bristolia bristolensis 3
Fig c 2 4 4 6 Bristolia insolens 4 Depth (meters) 8 Bristolia bristolensis 3 Figure Fossil evidence of evolution in a group of trilobites 10 3
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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
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Fig. 22-16 (a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic) Figure The transition to life in the sea Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)
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(a) Pakicetus (terrestrial)
Fig ab (a) Pakicetus (terrestrial) Figure The transition to life in the sea (b) Rhodocetus (predominantly aquatic)
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(c) Dorudon (fully aquatic)
Fig cd Pelvis and hind limb (c) Dorudon (fully aquatic) Figure The transition to life in the sea Pelvis and hind limb (d) Balaena (recent whale ancestor)
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Homology Homology is similarity resulting from common ancestry
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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
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Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat
Fig Humerus Radius Ulna Carpals Metacarpals Figure Mammalian forelimbs: homologous structures Phalanges Human Cat Whale Bat
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Comparative embryology reveals anatomical homologies not visible in adult organisms
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Pharyngeal pouches Post-anal tail Chick embryo (LM) Fig. 22-18a
Figure Anatomical similarities in vertebrate embryos Chick embryo (LM)
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Pharyngeal pouches Post-anal tail Human embryo Fig. 22-18b
Figure Anatomical similarities in vertebrate embryos Human embryo
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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
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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
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Homologous characteristic
Fig Branch point (common ancestor) Lungfishes 1 Amphibians Tetrapods 2 Mammals Tetrapod limbs Amniotes 3 Lizards and snakes Amnion 4 Crocodiles Figure Tree thinking: information provided in an evolutionary tree Homologous characteristic 5 Ostriches Birds 6 Feathers Hawks and other birds
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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
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NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Fig. 22-20
Figure Convergent evolution Flying squirrel
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Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution Islands have many endemic species that are often closely related to species on the nearest mainland or island Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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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
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Individuals in a population vary in their heritable characteristics.
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.
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Fig. 22-UN2
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Fig. 22-UN3
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You should now be able to:
Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace Describe Lamarck’s theories, and explain why they have been rejected Explain what Darwin meant by “descent with modification” List and explain Darwin’s four observations and two inferences Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Explain why an individual organism cannot evolve
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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