DARWIN’S THEORY
SC B-5: THE STUDENT WILL
DEMONSTRATE UNDERSTANDING
OF BIOLOGICAL EVOLUTION & THE
DIVERSITY OF LIFE
Inquiry Activity
 Page 368 in book
 Page 35 in notebook
 work in pairs
 When you have calculated your average length put it
on board so class average can be calculated
 Also record length of your shortest bean and longest
bean: What is the range of the bean length?
 CN: PAGE 112 NOTEBOOK
 TOPIC: Darwin’s theory of Evolution
 EQ: What inferences did Darwin make about Natural
Selection from his observations?
DEFINITIONS
1.
EVOLUTION: process by which modern organisms
have descended from ancient organisms
2. THEORY: well-tested explanation that unifies a
broad range of observations
Charles Darwin
 Englishman born in 1809
 After graduating in 1831
from University took job
as a naturalist on H.M.S.
Beagle & traveled around
the world
Darwin’s Voyage
Darwin
 During his travels,
Darwin made
numerous
observations &
collected evidence
that led him to
propose a
revolutionary
hypothesis about the
way life changes over
time.
Darwin’s Observations
1. Plants & animals
remarkably wellsuited to their
surroundings
2. Different organisms
lived in same type of
ecosystem Example:
grasslands of
Europe + rabbits but
grasslands in
Australia - rabbits
 Fossils: preserved
remains or evidence
of an ancient
organism
 Darwin studied
fossils from different
continents & noted
that some resembled
organisms still living
& some unlike any
creature he had ever
seen
Galapagos Islands
 Small group of
islands off Ecuador
 Climates varied from
hot & dry to rain
forest
 Each had different
flora & fauna
Galapagos Animals
Darwin’s Hypothesis
Darwin noticed that
characteristics of
many animals &
plants varied
noticeably among
different islands and
hypothesized that
they had a common
ancestor
Contemporary Ideas that shaped Darwin’s Ideas
 1785: James Hutton 1st to
present idea that Earth is
much older than Bible
would indicate



Looked at layers of
sedimentary rock with
fossils of sea creatures
now on mountain top
Looked at geological
processes that shape Earth
Reasoned that processes
seen today same in past
Origins of Evolutionary Thought
 Malthus: 1798
 Predicted human
population will grow
faster than the space &
food supplies needed to
sustain it
Origins of Evolutionary Thought
 Lamark: 1809
 proposed hypothesis of
inheritance of acquired
traits:
 if
parent became very
accurate with bow &
arrow after years of
practice  any child
born after would also
be very accurate with
bow & arrow
 Lyell: wrote Principles of
 Lyell’s work influenced
Geology (Darwin read 1st
vol. while on the Beagle)
 Said must explain past
events in terms of
processes observed now
Darwin 2 ways:
 1. He asked himself: If
Earth can change over
time why not living
organisms?
 2. He realized it would
take very long time for
change to be obvious
Origins of Evolutionary Thoughts
 Wallace: 1858
 Naturalist working in
Malaysia
 wrote Darwin
speculating on
mechanism of evolution
by natural selection 
induced Darwin to
publish Origin of the
Species in 1859
The Origin of the Species
 Darwin returned to
England in 1836 and
reviewed his
observations & notes
but did not publish
his book for 25 yrs
 Darwin proposed a
mechanism for
evolution that he
called: natural
selection
Artificial Selection
 One of Darwin’s most
important insights
was that members of
each species vary
from one another in
important ways.
 Darwin argued that
these small variations
were very important
using breeders as
example
Artificial Selection
 Humans choose the natural variations in a
species that they found useful and used
selective breeding to enhance the traits
desired.
Evolution by Natural Selection
 Struggle for Existence: members of each
species compete for available food, living
space, mates


Predators that are faster, better nourished, survive
longer, more likely to reproduce more thus passing
on those traits that made them faster
Prey that are slightly better at camouflage less likely
to be eaten, more likely to reproduce
Survival of the Fittest
 Darwin reasoned that a key factor in struggle
for existence was how well-suited an
individual is to its environment
 Fitness: the ability of an individual to survive
& reproduce in its specific environment
Adaptations
 Adaptation: any inherited characteristic that
increase’s an organisms chances of survival
 Can be:



Anatomical (structure of organism)
Physiological (function of organism)
Behavioral
Adaptations
Survival of the Fittest
 Darwin referred to
survival of the fittest
as natural selection
 Over time the
variants in traits that
offer an advantage
will have increasing
incidence in
population
Descent with Modification
 Term used by Darwin to explain why species
today look different from their ancestors:
A successful species will just reproduce, always
with some variation in traits until a new stressor
appears which will give an advantage to some
variations and a disadvantage to others
 Variations that give advantage will then become
more prevalent in population; others will
decrease in #’s

Common Descent
 Descent with modification implies all living
things have a common ancestor
Evidence of Evolution: 4 sources
1. Fossil Record
2. Distribution of
Species
 Dating & comparing
 Continental Drift helps
fossil shows
progression of species
over long periods of
time
 Many species have
disappeared
explain why similar
organisms on different
continents
Continental Drift
Evidence of Evolution
3. Homologous
Structures
 Darwin noticed striking
similarities in
vertebrates (also seen
in plants & algae)
 Vestigial Structures:
homologous structure
that have been reduced
in size, no longer serve
a purpose (appendix)
Evidence of Evolution
4. Embryology
 Many vertebrate
embryos go through
stage where they look
very similar to another
species
Summary of Darwin’s Theory
 1. individual organisms differ & some of this




variation is inheritable.
2. organisms produce more offspring than can
survive & many that do survive don’t reproduce
3. because there are more organisms than can
survive they must compete for limited resources
4. individuals best suited to their environment will
survive & reproduce passing their successful traits on
(causes species to change over time)
5. species today all descended from common
ancestors
Darwin’s Theory
Strengths
Weaknesses
 Most of Darwin’s
 Still does not explain
hypotheses have been
confirmed
 Is considered by many
to be the “grand
unifying theory of life
sciences”
how life began
 New information
always coming to light:
theories change over
time