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Introduction to a
Darwinian View of Life
Bio 204
Winter 2005
Lapsansky
Charles Darwin’s radical idea
(or was it?)
Meticulous observation
Considered numerous
possible relationships,
especially b/w animals
and their environment
2 main points:
Species evolved from
ancestral species
Natural selection was the
mechanism for this
evolutionary change
A desire to assign order (for practical and other
purposes) is at the heart of human understanding
Linnaeus developed the system of binomial
nomenclature
Figure 22.1
Early explanations for the great diversity of life on
earth did not utilize scientific methods
Darwin was trained as a natural theologian after
failing medical school
Figure 22.1
Observations of some species hinted at historical
connections and indicated that some change had
occurred over time
Transmutation (Erasmus Darwin)
Figure 22.1
Erasmus Darwin
Organic life beneath the shoreless waves
Was born and nurs'd in ocean's pearly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing.
Erasmus Darwin. The Temple of Nature. 1802.
(This poem hints at the fact that Lamarck and Erasmus
Darwin were contemporaries.)
Collecting evidence of changes affecting life on
earth, over long periods of time
…but was it gradual or catastrophic change?
Figure 22.1
James Hutton
Scottish geologist, 1795
Geologic mechanisms are slow and continuous,
producing gradual change
= Geologic gradualism
Jean Baptiste Lamarck
French invertebrate
natural historian, 1809
Proposed that life
forms evolved along
with Earth’s changes
used the fossil record
toward greater
complexity
Two Principles:
use / disuse
inheritance of acquired
characteristics
How did Lamarck explain
simple life forms?
Thomas Malthus
English political economist, 1798
Essay on human condition as related to overreproduction and limited resources
Georges Cuvier
French anatomist, 1813
“Essay on the Theory of the Earth” and
founded the science of paleontology
Catastrophism, to explain earth’s
history
Fig 22.3
Charles Lyell
Scottish geologist, 1830
Incorporated Hutton’s
gradualism into this widely read
book, “Principles of Geology”
The same slow geologic
mechanisms at work today have
always been at work
= Uniformitarianism
Darwin concluded that the earth
must be very old, and had a
copy of Lyell’s book with him
on the Beagle
Voyage of the Beagle
1831-1836
Voyage of the Beagle
1831-1836
Fig 22.5
Alfred Wallace
British naturalist, 1858
Letter from West Indies
with article to review and
forward to Lyell
Developed a theory of
evolution identical to the
one Darwin was working
on
Wallace and
Darwin jointly
present their ideas
(1858) to the
Linnaean Society of
London, 32 years
after the end of
Darwin’s voyage
“On the Origin of
Species” is
published for the
first time in 1859
On the Origin of Species
Descent with modification
(aka evolution) is the
explanation for life’s unity
and diversity
all organisms are related
via a common ancestor
adaptations developed as
descendents from a
common ancestor
moved into new habitats
(or the habitat changed)
Darwin’s metaphor for the history of life was a branching tree.
On the Origin of Species
Natural selection is the mechanism
3 inferences based on 5 basic observations
(as characterized by Ernst Mayr, 1982)
 Too many individuals for limited resources
 Those that have favorable traits are “more fit”,
survive and reproduce
 The traits of the survivors dominate in a population
and cause it to evolve
Darwin had synthesized some of the basic concepts in
population ecology and inheritance, at the dawn of the
Cell Theory (1839) and prior to Mendel’s genetics
experiments (1866).
Observation 1
Fig 22.8
Species have a great
potential for
reproduction
Populations would
increase exponentially
if all individuals
survived and
reproduced
Observation 2
Populations tend
to remain stable
over time,
except for mild
seasonal
fluctuations and
occasional
severe
fluctuations
Fig 52.17 Moose population on island in
Lake Superior
Observation 3
Natural resources are limited
Fig 52.19
Discussion in Malthus, “Essay on the Principle of Population”
helped to clarify this for Darwin
Inference 1:
Since more individuals are produced than can
be supported by the available resources but
population size remains stable, it means that
there must be a fierce struggle for existence
among individuals of a population, resulting
in the survival of a part, often a very small
part, of the offspring of each generation
In populations, more individuals are born than can
be supported by the environment
Only a fraction will survive to the next generation
(there is a struggle for existence)
Observation 4
No two individuals are exactly the same; rather,
every population displays enormous variability.
Fig 22.9
Observation 5
Much of this variation
is heritable
However, Darwin did
not know the
mechanism of
inheritance
Fig 1.3b
Inference 2:
Survival in the struggle for existence is not
random but depends in part on the
hereditary constitution of the surviving
individuals. This unequal survival
constitutes a process of natural selection.
Those with better traits survive and reproduce
Survival depends on an organism’s characters that
are, at least in part, inherited
More fit individuals will leave more offspring than
less fit individuals
Inference 3:
Over generations this process of natural
selection will lead to a continuing gradual
change of populations, that is, to evolution
and to the production of new species.
Unequal ability of individuals to survive and reproduce
leads to gradual change in a population
More favorable characters accumulate = Microevolution
(i.e. evolution in a population)
Macroevolution = origin of new species and other
taxonomic groups due to accumulation of change over long
periods of time.
Peter and Rosemary
Grant have been
working on
Galapagos finches
since 1973 on Isla
Daphne Major.
Geospiza fortis is a
seed-eater that cracks
seeds by grasping at
the base of the bill
and applying force.
Beak size is
correlated with
consumed seed size.
Are characteristics variable in a population? YES.
Is some of the variation among individuals heritable? YES.
Is there an excess of offspring, only some of which survive
to reproduce (due to limited natural resources)? YES.
Is survival and reproduction nonrandom? YES.
Other Evidence for Evolution
Organisms are
adapted to their
environments
Camouflage is
an example of
evolutionary
adaptation
Fig 22.10a A floral mantid.
Other evidence
Artificial selection
Fig 22.11b Vegetables developed
by humans from wild mustard plant
Other evidence
Examples of natural
selection over short
periods of time
Is it fair to call
this“natural”
selection?
How is it similar to
antibiotic resistance
among pathogenic
bacteria?
Fig 22.12 Evolution of resistance to
insecticides in insect populations
Other evidence
Homologous structures
Fig 22.14 Forearm bones in mammals
Other evidence
Fig 17.16 Ribosomal structure (large
subunit of bacterial ribosome)
Molecular “record” –
molecular homologies
Other evidence
Biogeography
Fig 34.32 Adaptive radiation of
Australian marsupials compared to
similarities among other mammals
Other evidence
Fossil record
Fossil Trilobites
Fig 22.7 Elephant evolution based
on fossils