1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 22 Descent with Modification: A Darwinian View of Life

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Darwin Introduces a Revolutionary Theory – Charles Darwin published On the Origin of Species by Means of Natural Selection Darwin made two major points in his book – He presented evidence that the many species of organisms presently inhabiting the Earth are descendants of ancestral species – He proposed a mechanism for the evolutionary process, natural selection

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Lamarck’s Theory of Evolution Lamarck hypothesized that species evolve – Through use and disuse and the inheritance of acquired traits – But the mechanisms he proposed are unsupported by evidence Figure 22.4

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Voyage of the Beagle During his travels on the Beagle – Darwin observed and collected many specimens of South American plants and animals Darwin observed various adaptations of plants and animals – That inhabited many diverse environments

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Darwin’s interest in the geographic distribution of species – Was kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South America Figure 22.5 England EUROPE NORTH AMERICA Galápagos Islands Darwin in 1840, after his return SOUTH AMERICA Cape of Good Hope Cape Horn Tierra del Fuego AFRICA HMS Beagle in port AUSTRALIA Tasmania New Zealand PACIFIC OCEAN Andes ATLANTIC OCEAN

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings From studies made years after Darwin’s voyage – Biologists have concluded that this is indeed what happened to the Galápagos finches Figure 22.6a–c (a) Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. (c) Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. (b) Insect eater. The green warbler finch (Certhidea olivacea) uses its narrow, pointed beak to grasp insects.

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Origin of Species Darwin developed two main ideas – Evolution explains life’s unity and diversity – Natural selection is a cause of adaptive evolution

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Descent with Modification The phrase descent with modification – Summarized Darwin’s perception of the unity of life – States that all organisms are related through descent from an ancestor that lived in the remote past

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In the Darwinian view, the history of life is like a tree – With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms Figure 22.7 Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Years ago Millions of years ago Deinotherium Mammut Stegodon Mammuthus Platybelodon Barytherium Moeritherium Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa)

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural Selection and Adaptation Evolutionary biologist Ernst Mayr – Has dissected the logic of Darwin’s theory into three inferences based on five observations

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation #1: For any species, population sizes would increase exponentially – If all individuals that are born reproduced successfully Observation #2: Nonetheless, populations tend to be stable in size – Except for seasonal fluctuations Observation #3: Resources are limited

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inference #1: Production of more individuals than the environment can support – Leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation #4: Members of a population vary extensively in their characteristics – No two individuals are exactly alike Observation #5: Much of this variation is heritable

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inference #2: Survival depends in part on inherited traits – Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals Inference #3: This unequal ability of individuals to survive and reproduce – Will lead to a gradual change in a population, with favorable characteristics accumulating over generations

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Artificial Selection In the process of artificial selection – Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summary of Natural Selection Natural selection is differential success in reproduction – That results from the interaction between individuals that vary in heritable traits and their environment If an environment changes over time – Natural selection may result in adaptation to these new conditions

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolution of Drug-Resistant Pathogens In humans, the use of drugs – Selects for pathogens that through chance mutations are resistant to the drugs’ effects Natural selection is a cause of adaptive evolution

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anatomical Homologies Homologous structures between organisms – Are anatomical resemblances that represent variations on a structural theme that was present in a common ancestor Figure 22.14 HumanCat Whale Bat

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparative embryology – Reveals additional anatomical homologies not visible in adult organisms Figure 22.15 Pharyngeal pouches Post-anal tail Chick embryo Human embryo

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vestigial organs – Are some of the most intriguing homologous structures – Are remnants of structures that served important functions in the organism’s ancestors

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Homologies Biologists also observe homologies among organisms at the molecular level – Such as genes that are shared among organisms inherited from a common ancestor

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sugar glider AUSTRALIA NORTH AMERICA Flying squirrel Figure 22.17 Some similar mammals that have adapted to similar environments (Convergent Evolution) – Have evolved independently from different ancestors

23. Copyright © 2005 Pearson Education, Inc. publishing as 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 Figure 22.18

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What Is Theoretical about the Darwinian 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