Ch. 22 : Descent with Modification - A Darwinian View of Life

1. Ch. 22: Descent with Modification - A Darwinian View of Life

2. Intro • A. Charles Darwin published On The Origins • of Species in 1859. • Evolution: • Natural Selection:

3. Evolutionary adaptation: a prevalence of • inherited characteristics that enhance • organisms’ survival and reproduction. Examples: Katydid - mimicry Creosote bush - toxins Bats - echolocation

4. The Historical Context for Evolutionary Theory

5. Western culture resists evolutionary views: • 1.Plato and Artistotle • 2.Judeo-Christian culture: “natural theology” • Carolus Linnaeus (1707-1778): Swedish • botanist tried to put in order the diversity • of life “for the greater glory of God.” • -Taxonomy: • Georges Cuvier (1769-1832): French • anatomist who developed paleontology, • the study of fossils. • Fossils: relics or • impressions of organ- • isms found in • sedimentary rock.

6. New layers of sediments cover older ones, • creating layers of strata. • Fossils within layers show that a succession • of organisms have populated Earth • throughout time. • Cuvier opposed evolution. • He advocated catastrophism: strata due • to a catastrophe (flood/drought) then area • repopulated by immigrating species.

7. Theories of geologic gradualism helped clear • the path for evolutionary biologists: • Scottish geologist James Hutton (1726- • 1797) proposed gradualism: • Scottish geologist • Charles Lyell (1797- • 1875) incorporated • gradualism to form a • theory called • uniformitarianism.

8. Hutton and Lyell had a large influence on • Darwin. •  If geological changes result from slow, • continuous processes, then the Earth must • be far older than the 6000 years assigned • by theologians from biblical inference. • Jean Baptiste Lamarck published his theory • of evolution in 1809. • Lamarck compared current species of • organisms with fossil forms and noticed • several lines of descent. • Lamarck’s method of evolution: 3.Example: Giraffe’s long neck

9. Darwinian Evolution • Born in 1809 in western England. • After graduating college, Darwin was • chosen to be a conversation companion • to Captain Robert FitzRoy, on the survey • ship Beagle for a voyage around the world. • Field research on the Beagle helped him • develop his view of evolution.

10. The Beagle’s main mission was to chart • S. America’s coast. • Darwin had a lot of time to explore the • areas. He collected thousands of exotic • specimens. • Darwin noticed that the organisms living • on the Galapagos Islands resembled • organisms found on the mainland • S. America. • Darwin took notice of the 13 types of • finches he collected. Their different beak • shapes correlated to the foodsource found • on the island they lived on.

12. By the early 1840’s, Darwin had developed • the major features of natural selection. • In 1858, Alfred Wallace, a young naturalist, • sent Darwin a manuscript containing a theory • of natural selection essentially identical to • Darwin’s. • The next year, Darwin published The Origin • of Species. • Two main points:

13. Descent with Modification = evolution Based on fossil evidence

14. Natural Selection: Ernst Mayr, an • evolutionary biologist, has dissected the • logic of Darwin’s theory into three inferences • based on five observations. 5 observations: 1 - Exponential fertility 2 - Stable population size 3 - Limited resources 4 - Individuals vary 5 – Heritable variation

15. 3 inferences: 1 - Struggle for existence 2 - Non-random survival 3 - Natural selection (differential success in reproduction) • We can summarize Darwin’s main ideas in • 3 points: • Natural selection is differential success in • reproduction (unequal ability of individuals • to survive and reproduce). • b.Natural selection occurs through an • interaction between the environment and • the variability inherent among the individual • organisms making up a population.

16. c. The product of natural selection is the • adaptation of populations of organisms • to their environment.

17. In each generation, environmental factors • filter heritable variations, favoring some over • others. • Differential reproduction: • Artificial selection:

19. While natural selection involves interactions • between individual organisms and their • environment, it is not individuals, but • populations that evolve. • Population: • Therefore, evolution is measured as the • change in relative proportions of heritable • variation in a population over a succession • of generations.

20. Examples of natural selection provide • evidence for evolution: • Insecticide- • resistance in • insects: • Over time, • insecticides • become less • effective as • the percentage • of insecticide- • resistant individuals • increases with • each generation. • Ex: DDT and • malathion

21. Drug-Resistance HIV: • Natural • Selection • favors • viruses • with a • resistance • to the • many HIV • drugs being • developed. • For patients treated with the drug 3TC, • which interferes with genome replication • in HIV, 3TC-resistant strains become • 100% of the population of HIV in just a • few weeks.

22. G. Other evidence for evolution: • Homology: Forearm: homologous structures • Vestigial organs: • Ex. whale/snake hindlimbs; wings on • flightless birds

23. Homologies in embryonic development: • -pharyngeal pouches

24. Pharyngeal Pouches and Tails

25. Homologies on a • molecular level:

26. Homologies reflect the taxonomic tree of • life.

28. Evolutionary relationships among species • are documented in their DNA and proteins • - in their genes and gene products. • Biogeography: • Species tend to be more closely related to • other species from the same area than to • other species with the same way of life, • but living in different areas. • Marsupials of Australia

29. The sugar glider and flying squirrel are similar in appearance. However, the sugar glider is more similar to other marsupials in Australia. This is an example of convergent evolution.

30. Islands provide good evidence for • evolution; islands often have species that • are found no where else in the world. • These species are called endemics. • Island organisms usually resemble species found on the nearest mainland. • Island chains or archipelagos, individual • may have different, but related species • as the first mainland invaders reached • one island and then evolved into several • new species as they colonized other • islands in the archipelago.

31. Ex. Drosophila of Hawaii Finches of the Galapagos Islands

33. Fossil evidence of evolution: • The succession of fossil forms is • compatible with the branches of the tree of • life. Ex. Fish  Amphibians  Reptiles  Mammals, Birds • Fossils show changes that occurred.