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Charles Darwin Evolutionary Thought and the Evidence for Evolution.

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Presentation on theme: "Charles Darwin Evolutionary Thought and the Evidence for Evolution."— Presentation transcript:

1 Charles Darwin Evolutionary Thought and the Evidence for Evolution

2 I.Evolution and Its Core Principles A.Evolution is a central theme in biology-it explains striking similarities and astonishing differences in the form, function, behavior, and ecology of living things.

3 B.Core principles of evolution: 1. All life is linked through a common ancestor 2. Populations of living things change with time (evolve) 3. The environment influences this change (natural selection) 4. Helpful traits are selected over less-helpful traits and become more common in the population (descent through modification).

4 Charles Darwin

5 A. Darwins contributionStory of Darwins voyage of discovery. End to medical studies, studies theology, sets sail as naturalist on HMS Beagle along coastal South America. II.Charles Darwin and the Theory of Evolution

6 B.Rich diversity of tropical life, mainland & island species, makes deep impression on young Darwin.

7 Darwins Voyage

8 Galapagos Islands


10 C. Darwins Theory of Evolution by Natural Selection 1.There is variation within a population 2.Some variations are helpful (allow organism to survive to pass on genes) 3.Some variations are NOT helpful (keep the organism from surviving and passing on genes)

11 4. Not all young produced in a generation can survive a. This leads to a struggle for existence. b. Survival of the fittest. c. Those that survive and reproduce are those with the good variations.

12 D. What is a SPECIES? 1.Group of similar organisms a. Structurally b. Biochemically 2. Can interbreed successfully in nature a. Offspring are healthy b. Offspring are fertile (can reproduce) THIS CANT HAPPEN, PEOPLE!!! THIS CAN!

13 E. This organisms is not a new species…Why? Mule

14 F. Origin of Species Speciation – evolution of one or more species from a single ancestor species. can be from: Isolation –geographic barrier (canyon, mountain, or island) separates 2 groups of the same species and they evolve separately.

15 G. Variation and Adaptation 1. Variation – differences between individual members of a population Members of a species are very similar, but differences can be observed, making each individual unique. May be caused by mutations

16 2. Mutations Changes in DNA base sequences Most are either neutral or harmful (rarely beneficial) Those that allow the organism to survive better in a particular environment are good & are more likely to be passed on to future generations.

17 3. Most variations are not caused by mutations A. Sexual reproduction combines genes from both parents B. Crossing over during meiosis can produce variations

18 4. Adaptation a. An inherited trait that increases the populations chances of survival & reproduction in a particular environment. b. Allows organisms to fit best into a particular niche (habitat and role)

19 H. Divergent Evolution Isolated populations of a species evolve independently of each other. Ex: polar bears and brown bears

20 I. Convergent Evolution Natural Selection produces analogous (similar) adaptations in different organisms in response to similar environments: Ex: African Serval cat & South American maned wolf These animals have similar ears, legs, acute hearing, habitat, and Occupy similar niches

21 J. Coevolution Species that interact closely often adapt to one another:

22 K. Adaptive Radiation Many different species evolve from one ancestral species – each new species has a different niche

23 III.Evolutionary Thinking before Darwin A.Rapid advances in new field of geology (spurred by need to find coal and iron to fuel Industrial Revolution) set stage for Darwins ideas.

24 B. Other biologists have an influence: 1.Darwin reads Lyells Principles of Geology; stressed antiquity of Earths history and its continual shaping by natural forces (evolution of land forms).

25 2.Lamarcks ideas about inheritance of acquired characteristics were wrong, but notion of change in organism over time was sound.

26 Jean Baptiste Lamarck Use and Disuse Inheritance of Acquired Characteristics

27 IV.Darwins Insights A.Tour of Galapagos Islands impresses Darwin with its diversity; striking correlation between form of finch species and their environments; similarities and differences with mainland species lead to first flash in inspiration: Darwins finches

28 Maybe the island species are derived from mainland species and have become different over time because of a change in the environment on the islands.

29 B.Back in England, Malthus book on limits to population growth has strong impact (struggle for existence, preservation of good traits, loss of bad traits). C.Wallaces letter outlining basic principles of natural selection spurs Darwin into taking his ideas public.

30 D.After fierce debate, Darwins thesis that organisms evolve over time in response to natural forces is accepted among most scientists about 15 years after publication of On the Origin of Species by Means of Natural Selection. (Means of natural selection are debated into modern times.)

31 E.Advances in genetics in the twentieth century yield the mechanism (DNA) through which natural selection operates, vindicating Darwins ideas.

32 V.Opposition to the Theory of Evolution A. Evolutionary theory, more than any other scientific theory, is regularly challenged. B. Much of the objection comes from a mistaken view of what a scientific theory represents.

33 C.Some of the evidence for evolution is historical in nature, and cannot be demonstrated experimentally; consistency in the evidence derived from many sources:

34 Biology: embryology, bio-chemistry Other disciplines: geology, nuclear chemistry More than 100 years of evidence has convinced most scientists that the core principles of evolution accurately describe the story of life on Earth.

35 VI. The Evidence for Evolution A. Fossils 1.The age of fossils found in sedimentary rocks can be determined using radioactive decay.

36 2. Fossils of simpler organisms are found in older rocks, newer rocks contain more complex organisms

37 Fossil Formation

38 B.Comparative morphology and embryology Similarities in form and structure (morphology) between otherwise different- appearing structures, that is organization of bones in fins of whales, wings of bat, paws of cat and gorilla, point to their common evolutionary origin (homology);

39 Early embryo development in all animals goes through similar stages, to the extent of producing structures not seen in adults of the more complex organisms (e.g., pharyngeal slits in humans).

40 Comparative Embryology

41 C. Homologous Structures – similar morphology, even if function is different, indicates a close evolutionary relationship

42 D. Analogous Structures – demonstrate organisms are not related evolutionarily – similar function, different morphology BAT WING INSECT WINGS BIRD WING

43 E. Advances in molecular biology reveal similarity in genes that control cellular function in very different organisms (same set of genes controls many early events in the development of the fruit fly and mouse); gene sequence of more distantly related organisms more different; rate of accumulation of gene mutations since split from common ancestor may allow one to deduce how long ago two groups of organisms diverged from each other.


45 F.Experimental evidence can demonstrate natural selection at work; Endlers experiments with guppies: In predator-free environments theres an increase in number of male guppies with large and brightly colored tails, because they are favored by females; but when predators are reintroduced the number of male guppies with smaller, less conspicuous tails increases again because the flashier fish are eaten by predators.

46 G. Evolution Observed: Peppered Moths Light moths Dark moths Light tree Dark tree Less pollution More pollution

47 Evolution

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