Historical Background to

Darwin's Theory of Evolution

Evolution is the core theme of biology

The 3 main beliefs about Origins

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%

1. Lack of knowledge on age of Earth2. The Concept of fixity of species3. Lack of scientific method4. Notion of separate creation for humans and animals

Four Factors that limited the development of theory of evolution

Plato (427-347 BC)

� Saw variations in plant and animal populations as imperfect representations of ideal forms

� Only the perfect forms of organisms were real: idealism, essentialism philosophy

Aristotle (384-322 BC) Plato’s student

� all living forms could be arranged on a scale of increasing complexity “scala naturae” (scale of nature)

� no vacancies and no mobility in this ladder of life

� species are fixed, permanent, and do not evolve

Bishop Ussher 1650

� Earth is very young � (based on Bible)

1st Day of creation: Sunday 23 October 4004 BC

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Carolus Linnaeusc. 1735

� Swedish physician and botanist: father of taxonomy

� He believed that species were permanent creations, “God creates, Linnaeus arranges”

� Wanted to organize the “scale of nature”

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Georges Cuvier (1769-1832):

� Opposed evolution, thought that boundaries between fossil layers corresponded to catastrophic events such as floods or droughts

� Catastrophism = Earth is young

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Founder of Paleontology (the study of fossils)

Natural Theology:

� saw the adaptation of organisms to their environment as evidence that the creator had designed each and every species for a particular purpose

� (based on Judeo-Christian culture)

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

James Hutton:

� In 1795 suggested Gradualism, profound change is the cumulative product of slow but continuous processes

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Charles Lyell

(1797-1875):

� Uniformitarianism� Embellished Hutton’s gradualism,

geological processes are so uniform that their rates and effects must balance out through time

� Earth is very oldhttp://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Jean Baptiste Lamarck(1744-1829)

� Individuals can evolve� Believed that evolution responded to an

organisms “felt needs”� modifications acquired during a lifetime can be

passed on to offspring� no evidence for this Ex mice tails

http://www.pbs.org/wgbh/evolution/religion/revolution/index.html

Published a theory of evolution in 1809 (year Charles Darwin was born)

DARWIN1809 -1885

� Darwin trained to be a clergyman� Beetlemania turned him into a naturalist� Lyell and Hutton made him rethink the age of the

Earth� Got a position as the Naturalist on a 5 year voyage

http://www.pbs.org/wgbh/evolution/darwin/diary/

Beagle Voyage (1831-1836)

• Naturalist aboard the Beagle• Collected plant & Animal specimens• Took Lyell’s Book on Geology with him• Visited many places including Galapagos

http://www.pbs.org/wgbh/evolution/darwin/diary/

500 miles off coast of South America

New Volcanic Islands

Organisms migrated to Islands

•Developed idea’s on Evolution after the voyage.•Didn’t recognize what he was seeing

•Finches and Tortoises

DARWINAfter the Voyage

� Darwin developed his theory of Natural Selection� What inspired him?

� Hutton - Gradualism � Lyell - Earth is Old� Farmers/Animal Breeder - Variation in populations� Malthus - Populations grow rapidily

- Not enough resources for all offspring

http://www.pbs.org/wgbh/evolution/darwin/diary/

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

In nature, animals and plants produce more offspring than can survive.

This leads to a struggle for existence.

DARWIN reads Malthus1838In 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.

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

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)

Darwin’s Explanatory Model of Natural Selection

� Every population has such high fertility that its size would increase exponentially if not constrained. (source: Malthus)

Fact - #1

Fact - #2� The size of populations, except for

temporary annual fluctuations, remain stable over time. (source: observation)

Fact - #3� The resources available to every species

are limited (source: observation & Maltus)

� Inference 1. There is intense competition (struggle for existence) among the members of a species.

Fact - #4� No two individuals of a population are

exactly the same: (source: animal breeders & taxonomists)

� � Inference 2. Individuals of a population

differ from each other in the probability of survival

Fact - #5� Many of the differences among the

individuals of a population are, at least in part, heritable. (source: animal breeders)

� Inference 3. Natural selection, continued over many generations, results in evolution.

To sum up:� Populations evolve, not individuals.� Every species produces vastly more offspring

than can survive from generation to generation� All individuals of a population differ genetically

from each other.� They are exposed to the adversity of the

environment, and almost all of them perish or fail to reproduce.

� Only a few of them (on average two per set of parents) survive and reproduce.

� There survival is not random, but is aided by the possession of certain attributes that favor survival

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

Truth or Misconception? (cont.)

� Evolution is concerned with the good of the individual� Evolution is concerned with the good of the species� Natural selection picks organisms that are best adapted

to their environment� Humans are better adapted than Dolphins� Survival of the fittest: Lions are fitter than zebras� Evolution is the creation of new species� An Elk with bigger antlers is fitter than the one with

smaller antlers

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