Transcript Historical Background to Darwin`s Theory of Evolution

Developing the
Theory of Evolution
Evolution is the core theme of
biology
“Nothing in biology makes sense except in the light of
evolution”
Theodosius Dobzhansky
Pre-Darwin
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Naturalists of the 1700s
 were pre-occupied with naming new
species
 accepted a limited time scale
 assumed the fixity of species
 used newly invented microscopes and
telescope to look at embryos and stars
 recognized that fossils existed of animals
unknown in their explorations
Plato (427-347 BC)
Stated that variations in plant and
animal populations as being
imperfect representations of ideal
forms
 Only the perfect forms of organisms
were real: idealism, essentialism
philosophy
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Aristotle (384-322 BC) Plato’s student
Believed all living forms could be
arranged on a scale of increasing
complexity “scala naturae” (scale of
nature), with no vacancies and no means
to improve on this ladder of life.
 species are fixed, permanent, and do not
evolve (Stability of Species)
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Natural Theology:
based on Judeo-Christian culture (old
testament)
 Argued that adaptations in organisms
were planned by the creator.
- each and every species designed for a
particular purpose
 Forms today’s Intelligent design theory

Thinkers of the 19th Century
European colonialism leads to discovery
that the number of species is very large.
 Maybe species can change after all?
 Although this was discussed in numerous
circles, it was contrary to religious
teachings and dismissed as heresy.

Georges Cuvier (17691832):
Founder of Paleontology (the study of
fossils)
Opposed evolution
Thought that boundaries between fossil
layers corresponded to catastrophic
events such as Noah’s flood or
droughts
Developed the theory of catastrophism
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The oldest
fossils are
in the oldest
strata
James Hutton:(1726 - 1797)
Scottish Geologist
In 1795 suggested Gradualism - profound change is the
cumulative product of a slow but continuous process.
He looked at a present day process like erosion by
water and believed that these processes operating
over millions of years could have created
the geologic features we see today.
Charles Lyell (1797-1875):
Uniformitarianism –
An embellishment on Hutton’s gradualism, geological
processes are so uniform that their rates and effects must
balance out through time
Suggested the Earth was hundreds of millions of years
old.
Darwin took only three books with him on the Beagle.
One was Lyell’s book Principles of Geology
•Jean Baptiste Lamarck (17441829)
- The Inheritance of Acquired Characteristics
- environmental pressures require animals to strive
(unconsciously) toward higher branching pathways of
perfection
- Believed that evolution responded to organisms “felt
needs” i.e. ‘use and disuse’: examples: biceps of
blacksmith, giraffes neck
- inheritance of acquired characteristics: modifications
acquired during a lifetime can be passed on to offspring
- Although wrong, his thinking was visionary. (Environment)
Erasmus Darwin (17311802)
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Charles Darwin’s grandfather
observed adaptations of all
kinds including protective
coloration
noted intricate web of
ecological relationships
among different forms of life
estimated the antiquity of the
earth at “millions of ages”
recognized that through “a
certain similitude on the
features of nature … that the
whole is one family of one
parent”
believed in acquired heritable
Natural Selection
Charles Darwin
(1809-1882)

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originally intended to
study medicine at
Edinburgh; later went
to Cambridge
left to go as a naturalist
on the voyage of the
Beagle in 1831 to South
America
DARWIN

Darwin used 2 ideas from
Hutton and Lyell:

If geological changes results
from slow continuous changes
then earth must be older than
6000 years (natural theologian
calculation)
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Very slow and subtle
processes persisting over a
great length of time can cause
substantial change
•In 1831 he left on a 5 year voyage on board
the Beagle to survey the coast of South
America.
•He stopped off at the Galapagos Islands for
five weeks where the diversity of the plants and
animals amazed him.
•In 1836 he returned to England
•In 1859 published On the Origin of Species
•What ideas influenced Darwin?
Darwin saw variation within
species on the different
Islands.
But didn’t fully understand
what he saw till he returned
to England
Darwin’s Finches
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Thomas Malthus published his
Essay on the Principles of
Population - “survival of the fittest”
 shows
the tendency of life to multiply
faster than its food supply, which leads
to a struggle for existence

The Economist Malthus explained
population growth to Darwin
 Populations
breed rapidly
 But populations don’t grow unchecked
(Limiting Factors)
 Organisms need to breed to maintain
their species
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This with his observations, he could
see now how variations could arise
within species.
Comparison of Lamarck’s Theory
with that of Darwin
Darwin’s Theory of Natural
Selection
 All
organisms exhibit variability
 All organisms reproduce more offspring
than survive
Therefore, it must be that:
 Those individual variants best fitted to
their environments survive
 Those less well fitted fail to reproduce
 The characteristics thus favored by
selective pressure are passed on to the
next generation
The End