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 Theories of Gradualism Gradualism is the idea that profound change can take place through the cumulative effect of slow but continuous processes

3. 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

4. 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 The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past In the Darwinian view, the history of life is like a tree with branches representing life’s diversity

5. 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

6. 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

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation #2: Populations tend to be stable in size, except for seasonal fluctuations Observation #3: Resources are limited 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

8. 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

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Observation #5: Much of this variation is heritable 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

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Summary of Natural Selection Natural selection is differential success in reproduction from interaction between individuals that vary in heritable traits and their environment Natural selection produces an increase over time in adaptation of organisms to their environment If an environment changes over time, natural selection may result in adaptation to these new conditions Video: Seahorse Camouflage Video: Seahorse Camouflage

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Natural Selection in Action Two examples provide evidence for natural selection: the effect of differential predation on guppy populations and the evolution of drug- resistant HIV

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Homology, Biogeography, and the Fossil Record Evolutionary theory provides a cohesive explanation for many kinds of observations

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Homology Homology is similarity resulting from common ancestry

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anatomical Homologies Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Comparative embryology reveals anatomical homologies not visible in adult organisms

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vestigial organs are remnants of structures that served important functions in the organism’s ancestors

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Molecular Homologies Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some similar mammals that have adapted to similar environments have evolved independently from different ancestors

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Fossil Record The succession of forms observed in the fossil record is consistent with other inferences about the major branches of descent in the tree of life