Descent with Modification: A Darwinian View of Life Chapter 22 Descent with Modification: A Darwinian View of Life

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

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

Fig. 22-1 Figure 22.1 How can this beetle survive in the desert, and what is it doing?

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

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.

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

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

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

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

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

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

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

Fig. 22-4 Figure 22.4 Acquired traits cannot be inherited

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

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

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

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

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

Fig. 22-5a Figure 22.5 The voyage of HMS Beagle Darwin in 1840

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

Video: Galápagos Islands Overview Video: Blue-footed Boobies Courtship Ritual Video: Albatross Courtship Ritual Video: Galápagos Sea Lion Video: Soaring Hawk Video: Galápagos Tortoises Video: Galápagos Marine Iguana Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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

(a) Cactus-eater (c) Seed-eater (b) Insect-eater Fig. 22-6 Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater

(a) Cactus-eater Fig. 22-6a Figure 22.6 Beak variation in Galápagos finches (a) Cactus-eater

(b) Insect-eater Fig. 22-6b Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater

Fig. 22-6c Figure 22.6 Beak variation in Galápagos finches (c) Seed-eater

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

Darwin developed two main ideas: 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

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

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

Fig. 22-7 Figure 22.7 “I think . . .”

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

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

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

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

Observation #1: Members of a population often vary greatly in their traits Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-10 Figure 22.10 Variation in a population

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

Fig. 22-11 Spore cloud Figure 22.11 Overproduction of offspring

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

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

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

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

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

(a) A flower mantid in Malaysia (b) A stick mantid in Africa Fig. 22-12 (a) A flower mantid in Malaysia (b) A stick mantid in Africa Figure 22.12 Camouflage as an example of evolutionary adaptation

(a) A flower mantid in Malaysia Fig. 22-12a Figure 22.12 Camouflage as an example of evolutionary adaptation (a) A flower mantid in Malaysia

(b) A stick mantid in Africa Fig. 22-12b Figure 22.12 Camouflage as an example of evolutionary adaptation (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 drug-resistant 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

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 22.13 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

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 22.13 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”

Area of colored spots (mm2) colored spots Number of Fig. 22-13b RESULTS 12 12 10 10 8 8 Area of colored spots (mm2) colored spots Number of 6 6 4 4 2 2 Figure 22.13 Can predation result in natural selection for color patterns in guppies? Source population Transplanted population Source population Transplanted population

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

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

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

Fig. 22-14 100 Patient No. 1 Patient No. 2 75 Percent of HIV resistant to 3TC 50 Patient No. 3 Figure 22.14 Evolution of drug resistance in HIV 25 2 4 6 8 10 12 Weeks

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 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 22.15 Fossil evidence of evolution in a group of trilobites 2 1 Latham Shale dig site, San Bernardino County, California

Bristolia harringtoni 14 Fig. 22-15b 12 Depth (meters) Bristolia harringtoni 2 14 16 18 Bristolia mohavensis 1 2 Figure 22.15 Fossil evidence of evolution in a group of trilobites Latham Shale dig site, San Bernardino County, California 1

2 4 6 Depth (meters) 4 Bristolia insolens 4 8 Bristolia bristolensis 3 Fig. 22-15c 2 4 4 6 Bristolia insolens 4 Depth (meters) 8 Bristolia bristolensis 3 Figure 22.15 Fossil evidence of evolution in a group of trilobites 10 3

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) Figure 22.16 The transition to life in the sea Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

(a) Pakicetus (terrestrial) Fig. 22-16ab (a) Pakicetus (terrestrial) Figure 22.16 The transition to life in the sea (b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic) Fig. 22-16cd Pelvis and hind limb (c) Dorudon (fully aquatic) Figure 22.16 The transition to life in the sea Pelvis and hind limb (d) Balaena (recent whale ancestor)

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

Humerus Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat Fig. 22-17 Humerus Radius Ulna Carpals Metacarpals Figure 22.17 Mammalian forelimbs: homologous structures 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

Pharyngeal pouches Post-anal tail Chick embryo (LM) Human embryo Fig. 22-18 Pharyngeal pouches Post-anal tail Figure 22.18 Anatomical similarities in vertebrate embryos Chick embryo (LM) Human embryo

Pharyngeal pouches Post-anal tail Chick embryo (LM) Fig. 22-18a Figure 22.18 Anatomical similarities in vertebrate embryos Chick embryo (LM)

Pharyngeal pouches Post-anal tail Human embryo Fig. 22-18b Figure 22.18 Anatomical similarities in vertebrate embryos 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

Homologous characteristic Fig. 22-19 Branch point (common ancestor) Lungfishes 1 Amphibians Tetrapods 2 Mammals Tetrapod limbs Amniotes 3 Lizards and snakes Amnion 4 Crocodiles Figure 22.19 Tree thinking: information provided in an evolutionary tree Homologous characteristic 5 Ostriches Birds 6 Feathers Hawks and other birds

Convergent evolution does not provide information about ancestry 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

NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Fig. 22-20 Figure 22.20 Convergent evolution Flying squirrel

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

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

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

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.

Fig. 22-UN2

Fig. 22-UN3

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

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