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

1. What is our current working definition of evolution? A new era of biology began in 1859 when Charles Darwin published The Origin of Species Evolution can be defined by Darwin’s phrase descent with modification It is also considered a change in allele frequencies. 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?

Examples of evolution. Squirrel!

He developed the two-part, or binomial, system of naming species Carolus Linnaeus (1707-1778) was a Swedish physician and botanist who sought to classify life’s diversity “for the greater glory of God.” He developed the two-part, or binomial, system of naming species iInterpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose (clearly he did not support evolution) Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms He was not a proponent of evolution. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

A little fossil background. 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

Briefly describe the beliefs of the following individuals: Georges Cuvier (1769-1832) observed that the older the stratum, the more dissimilar its fossils were to current life forms. Also noted that from one layer to the next, some new species appeared while others disappeared. He staunchly opposed evolution, but advocated catastrophism Periodic catastrophes destroyed many of the species living in an area, and the area was repopulated by species immigrating in from other areas.

In contrast, other scientists suggested that profound change could take place through the cumulative effect of slow but continuous processes.

This view strongly influenced Darwin’s thinking In 1795, 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 published his hypothesis in 1809, the year Darwin was born. He proposed two ideas: use and disuse 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

Inheritance of Acquired Traits

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 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

His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands Figure 22.5 The voyage of HMS Beagle For the Discovery Video Charles Darwin, go to Animation and Video Files. AFRICA Pinta Genovesa Marchena Equator SOUTH AMERICA Santiago Daphne Islands Pinzón AUSTRALIA Fernandina PACIFIC OCEAN Isabela Andes Cape of Good Hope Santa Cruz Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego

Darwin observed geological phenomena that challenged the current idea that the Earth was only 6000 years old He also observed finches that had very similar traits, but also differed in ways that made them more suitable for their environment. He hypothesized that the Galapagos had been colonized by organisms that had strayed from South America and then diversified, giving rise to new species on various islands

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

Darwin’s Focus on Adaptation An adaptation is an inherited characteristic of an organism that enhances its survival and reproduction in specific environments. 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

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 Natural selection 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 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

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

Fig. 22-10 Observation #1: Members of a population often vary greatly in their traits 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

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

Therefore: 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

Cornucopians vs. Malthusians Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources Cornucopians vs. Malthusians 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

Note that individuals do not evolve; populations evolve over time 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

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)

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

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