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Developing the
Theory of Evolution
Chapter 19
Begin by reading Pg’s 640-649.
Evolution is the core theme of
biology
“Nothing in biology makes sense except in the light of
evolution”
Theodosius Dobzhansky
Key Terms:
Evolution – The relative changes in the
characteristics of populations that occurs
over time (several generations).
 Adaptation – Any trait that helps an
organism survive and reproduce in a
particular environment.
 Variation – a different form of any
particular trait.

 Discuss
the familiar example of the Peppered
Moth (pg. 644)
Natural vs. Artificial Selection

Natural – change that occurs because
organisms with particular traits help them
survive and reproduce under certain
environmental conditions.
 Must

have natural diversity within the population.
Artificial – occurs where a trait is selected
for by humans regardless of the health of
the organism.
Pre-Darwinian lead up to the
THEORY of Evolution

Plato (427-347 BC); Aristotle (384-322
BC) - Plato’s
 Idealism
- Stated that variations in plant and
animal populations as being imperfect
representations of ideal forms
 species are fixed, permanent, and do not
evolve (Stability of Species)
Pre-Darwin
Natural Theology:
 This is today’s - Intelligent design theory
 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
Pre-Darwin

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
The Changing Minds of the of
th
the 19 Century

European colonialism leads to the
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
in the Bible (Noah’s flood or droughts)
Developed the theory of catastrophism

The oldest
fossils are
in the oldest
strata
Charles Lyell (1797-1875):
Uniformitarianism –
An embellishment on Hutton’s gradualism theory –
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 (1744-1829)
- 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)
Thomas Malthus


published an essay on the Principles
of Population - “survival of the fittest”
Malthus explained population growth
to Darwin:
 Populations
need to reproduce and will
breed rapidly.
 This will cause competition between
members of the population for resources
(Limiting Factors).
 Those who have the ability to get
resources will survive.

This idea helped Darwin explain &
understand how variations could
arise within species.
Alfred Wallace



a British naturalist and explorer.
Independently conceived the theory of
evolution through natural selection.
He was considered the 19th century's
leading expert on the geographical
distribution of animal species and is
sometimes called the "father of
biogeography“.
Wallace became a ‘spiritualist’ and could
not extend the ideas of evolution on to
humans.
Charles Darwin - (1809-1882)



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 Video
•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.
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

Who would:
 Crack
open hard nuts? pick insects out of
cracks in trees? Etc…..
Darwin’s Published Works






Darwin reached England in 1836
met Charles Lyell
talked with stock breeders and dabbled in
breeding himself
read Malthus in October 1838
was a friend of Alfred Russel Wallace
(1823-1913) who arrived at the theory of
natural selection at the same time
presented his views with Wallace before
publication of On the Origin of Species
Darwin cont…


Charles Darwin published:
 “On the Origin of Species by
Means of Natural Selection,
or the Preservation of
Favoured Races in the
Struggle for Life.” on
November 24, 1859
It was an overnight bestseller
Note: Darwin never used the word evolution in his book, and the word
evolved only occurred once (the last word of the book).
Darwin referred to: Descent with modification
Comparison of Lamarck’s Theory
with that of Darwin
Darwin’s Theory of Natural Selection
(Main Points)
All organisms exhibit variability
 All organisms reproduce more
offspring than can survive so
competition exists.

Therefore, it must be that:
Those individuals best suited to their
environments survive and reproduce.
 Any changes in a population are slow
and gradual

The End
Evidence Supporting the Modern
Theory of Evolution - Chapter 19.3

Evidence Available to Darwin
 Fossils
 Taxonomy
 Comparative
Anatomy
 Comparative Embryology
 Biogeography

Modern Technologies
 Molecular
Biology
Fossil Record

Fossils:
 Are
remains or ‘imprints’ of past life
 Are preserved in sediments
 occur in layers (strata)
 Indicate the presence of species that many no
longer occur, or resemble forms of modern
species.
Strata layers in Rocks
Fossilized remains of a bird like dinosaur Archeopteryx
Fossil trilobite
Fossils in Amber
Fossil Jellyfish
Relative aging of Fossils
Fossils distributed consistently throughout
strata of same age.
 The order of fossil appearance shows that
more complex forms of life appear in
higher strata’s after simpler forms below.
 Recent fossils (new/top strata layers) more
closely resemble modern day organisms.

Absolute Age - Fossils
Calculate the
Half Lives
Evidence for Evolution

Evidence Available to Darwin
 Fossils
 Taxonomy
 Comparative
Anatomy
 Comparative Embryology
 Biogeography
Taxonomy
The hierarchical classification system
developed by Linnaeus.
 This system implies species can be
grouped together based on their
relatedness.

 Bears

with bears, bees with other bees, etc…
A family tree can be made implying
descent
Family Tree of Bears
Evidence for Evolution

Evidence Available to Darwin
 Fossils
 Taxonomy
 Comparative
Anatomy
 Comparative Embryology
 Biogeography
Comparative Anatomy
Compares the anatomical structures from
different organisms.
 Similar structures in two or more species
are called homologous structures.
 Homologous structures may perform
different tasks in different organisms.

Homologous forelimbs
Family Tree of the Horse (Equus)
Evidence for Evolution

Evidence Available to Darwin
 Fossils
 Taxonomy
 Comparative
Anatomy
 Comparative Embryology
 Biogeography
Comparative Embryology
Embryos (young stage of organisms are
compared)
 Show similar features due to shared
ancestry
 All vertebrates have

 tails
 gill-like
branchial arches
Where are we????
Evidence for Evolution

Evidence Available to Darwin
 Fossils
 Taxonomy
 Comparative
Anatomy
 Comparative Embryology
 Biogeography
Biogeography
Helps to explain the distribution of species.
 Many related species occur across the
earth.
 Isolated areas (islands, Australia) often
have unique species.
 Biogeography explained by continental
drift of plates and speciation.

Map of Oceanic Crust Ages in the
Atlantic
Map of Earthquake Epicenters,
1980-1990
Molecular Biology



Not available to Darwin in 1800’s
Includes comparisons of
 protein sequences
 DNA sequences
 cytochrome c (from mitochondria)
 chloroplast genomes (plants only)
Used to developed phylogenetic trees
(hypothesized relationships)