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Historical Background to Darwin's Theory of Evolution.

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Presentation on theme: "Historical Background to Darwin's Theory of Evolution."— Presentation transcript:

1 Historical Background to Darwin's Theory of Evolution

2 Evolution is the core theme of biology The 3 main beliefs about Origins

3 Naturalistic Evolution: Man has developed over millions of years from less advanced forms of life. God had no part in this process. Creationist view: God created man pretty much in his present form at one time within the last 10,000 years Theistic evolution: Man has developed over millions of years from less advanced forms of life, but God guided this process, including man's creation. 47% 40% 9%

4 1. Lack of knowledge on age of Earth 2. The Concept of fixity of species 3. Lack of scientific method 4. Notion of separate creation for humans and animals Four Factors that limited the development of theory of evolution

5 Plato ( BC) n Saw variations in plant and animal populations as imperfect representations of ideal forms n Only the perfect forms of organisms were real: idealism, essentialism philosophy

6 Aristotle ( BC) Plato’s student n all living forms could be arranged on a scale of increasing complexity “scala naturae” (scale of nature) n no vacancies and no mobility in this ladder of life n species are fixed, permanent, and do not evolve

7 Bishop Ussher 1650 n Earth is very young (based on Bible) 1st Day of creation: Sunday 23 October 4004 BC

8 Carolus Linnaeus c n Swedish physician and botanist: father of taxonomy n He believed that species were permanent creations, “God creates, Linnaeus arranges” n Wanted to organize the “scale of nature”

9 Georges Cuvier ( ): n Opposed evolution, thought that boundaries between fossil layers corresponded to catastrophic events such as floods or droughts n Catastrophism = Earth is young Founder of Paleontology (the study of fossils)

10 Natural Theology: n saw the adaptation of organisms to their environment as evidence that the creator had designed each and every species for a particular purpose n (based on Judeo-Christian culture)

11 James Hutton: n In 1795 suggested Gradualism, profound change is the cumulative product of slow but continuous processes

12 Charles Lyell ( ): n Uniformitarianism n Embellished Hutton’s gradualism, geological processes are so uniform that their rates and effects must balance out through time n Earth is very old

13 Jean Baptiste Lamarck ( ) n Individuals can evolve n Believed that evolution responded to an organisms “felt needs” n modifications acquired during a lifetime can be passed on to offspring n no evidence for this Ex mice tails Published a theory of evolution in 1809 (year Charles Darwin was born)

14 DARWIN n Darwin trained to be a clergyman n Beetlemania turned him into a naturalist n Lyell and Hutton made him rethink the age of the Earth n Got a position as the Naturalist on a 5 year voyage

15 Beagle Voyage ( )  Naturalist aboard the Beagle  Collected plant & Animal specimens  Took Lyell’s Book on Geology with him  Visited many places including Galapagos

16 500 miles off coast of South America New Volcanic Islands Organisms migrated to Islands


18  Developed idea’s on Evolution after the voyage.  Didn’t recognize what he was seeing  Finches and Tortoises

19 DARWIN After the Voyage n Darwin developed his theory of Natural Selection n What inspired him? u Hutton - Gradualism u Lyell - Earth is Old u Farmers/Animal Breeder - Variation in populations u Malthus - Populations grow rapidily - Not enough resources for all offspring

20 All populations have variation Darwin knew many farmers and animal breeders. From them and his own research he knew all individuals in a population are different.

21 In nature, animals and plants produce more offspring than can survive. This leads to a struggle for existence. DARWIN reads Malthus 1838 In 1838, Darwin reads for amusement Malthus’s book Population. Darwin see that favourable variations in a population would tend to be preserved, and unfavourable ones to be destroyed. He at last has a theory by which to work.

22 Darwin publishes the Origin of Species:1865 Didn’t publish is ideas for 20 years!!! Why? Wallace comes up with the idea of Natural Selection independently of Darwin. Forces Darwin to finally publish his book on Evolution

23 Darwin’s Five major theories of Evolution 1. The nonconstancy of species (species can evolve) 2. The descent of all organisms from common ancestors (branching evolution) 3. The gradualness of evolution (evolution takes time) 4. The multiplication of species (speciation: formation of new species) 5. Natural selection (the mechanism of evolution)

24 Darwin’s Explanatory Model of Natural Selection n Every population has such high fertility that its size would increase exponentially if not constrained. (source: Malthus) Fact - #1

25 Fact - #2 n The size of populations, except for temporary annual fluctuations, remain stable over time. (source: observation)

26 Fact - #3 n The resources available to every species are limited (source: observation & Maltus) n Inference 1. There is intense competition (struggle for existence) among the members of a species.

27 Fact - #4 n No two individuals of a population are exactly the same: (source: animal breeders & taxonomists) n n Inference 2. Individuals of a population differ from each other in the probability of survival

28 Fact - #5 n Many of the differences among the individuals of a population are, at least in part, heritable. (source: animal breeders) n Inference 3. Natural selection, continued over many generations, results in evolution.

29 To sum up: n Populations evolve, not individuals. n Every species produces vastly more offspring than can survive from generation to generation n All individuals of a population differ genetically from each other. n They are exposed to the adversity of the environment, and almost all of them perish or fail to reproduce. n Only a few of them (on average two per set of parents) survive and reproduce. n There survival is not random, but is aided by the possession of certain attributes that favor survival

30 Truth or Misconception?  Evolution has a plan for us  Humans are the pinnacle of Evolution  Species evolve by choice  Humans have finished evolving  Natural selection causes changes in an organism  Changes in your physical character's an individuals life will be passed on to your offspring

31 Truth or Misconception? (cont.) n Evolution is concerned with the good of the individual n Evolution is concerned with the good of the species n Natural selection picks organisms that are best adapted to their environment n Humans are better adapted than Dolphins n Survival of the fittest: Lions are fitter than zebras n Evolution is the creation of new species n An Elk with bigger antlers is fitter than the one with smaller antlers

32 1. Organisms reproduce like organisms 2. In most species only a small percentage of the offspring will actually survive to reproduce 3. There are variations in individuals in a given population & these variations can be passed on. 4. Whether an individual will survive to breed depend upon the interaction between the organism, other organisms & the environment. Some variations will be favorable. These variations will become more common from one generation to the next. 5. Given time natural selection will lead to different groups of organisms (speciation)nn

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