Historical
Background to
Darwin's Theory
of Evolution
Evolution is the core theme
of biology
The 3 main beliefs about Origins
Creationist view:
47%
God created man pretty much in his present form at
one time within the last 10,000 years
Theistic evolution:
40%
Man has developed over millions of years from less
advanced forms of life, but God guided this
process, including man's creation.
Naturalistic Evolution: 9%
Man has developed over millions of years from less
advanced forms of life. God had no part in this
process.
Four Factors that limited the development
of theory of evolution
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
Plato (427-347 BC)
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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
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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
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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 Linnaeus
c. 1735
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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):
Founder of Paleontology
(the study of fossils)
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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
Natural Theology:
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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:
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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):
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Uniformitarianism
Embellished Hutton’s gradualism,
geological processes are so uniform
that their rates and effects must
balance out through time
Earth is very old
http://www.pbs.org/wgbh/evolution/religion/revolution/index.html
Jean Baptiste Lamarck
(1744-1829)
Published a theory of evolution in
1809 (year Charles Darwin was born)
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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
DARWIN
1809 -1885
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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)
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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
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Finches
and Tortoises
DARWIN
After the Voyage
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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 variation
Darwin knew many farmers and animal breeders. From them and his
own research he knew all individuals in a population are different.
DARWIN reads Malthus
1838
In 1838, Darwin reads for amusement
Malthus’s book Population.
In nature, animals and plants produce more offspring than
can survive.
This leads to a struggle for existence.
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
Fact - #1
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Every population has such high fertility
that its size would increase exponentially if
not constrained. (source: Malthus)
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Fact - #2
The size of populations, except for
temporary annual fluctuations, remain
stable over time. (source: observation)
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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.
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Fact - #4
No two individuals of a population are
exactly the same: (source: animal breeders &
taxonomists)
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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)
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Inference 3. Natural selection, continued
over many generations, results in evolution.
To sum up:
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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?
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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.)
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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