Biology 821
Evolution—The Theory and
Its Supporting Evidence
I. Evolution is a theory (subject to
revision and change)
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In Biology a theory is an overarching
principle, supported by evidence
Evolution provides the framework
for modern biology
A hot topic long before Darwin and
Wallace suggested a mechanism
II. Evolution is change over time
• It occurs in populations, not in
individuals
• It explains how new organisms are
created
III. History
• Greek philosopher Anaximander (~2,500
years ago) – simpler life forms gave rise to
complex life forms
• Aristotle – species were fixed and did not
change
• Judeo-Christian culture - species were
created by the Divine Creator
Georges Buffon
• Fossils were ancient
forms of modern
organisms (1766)
• Earth is more than
6000 years old
• Studied fossils
scientifically (1800s)
• Comparisons of
fossils among rock
strata led him to
believe natural
catastrophes
periodically wiped out
existing species
Georges Cuvier
Jean Baptiste de Lamarck
• Fossils suggested that life
forms change (1809)
•Current organisms evolved
from past ones
•Organisms respond to
changes in their environment
by developing or changing
their structure
•wrongly thought acquired
characteristics could be
inherited
IV. Darwin
• 1859 - Charles Darwin published
Origin of Species.
– Proposed a different mechanism to
account for changes in a species
– Natural Selection
A sea voyage (1831-6) helped Darwin
frame his theory of evolution
Charles Darwin, 1859
1874
• H.M.S. Beagle cruise 1831-1836
www.rit.edu/~rhrsbi/GalapagosPages/Darwin.html
Charles Lyell
• Author of “Principles
of Geology”
• Geologic changes
occur slowly through
natural forces, bringing
about changes in the
earth’s surface
• While on the voyage of the HMS Beagle in
the 1830s, Charles Darwin observed
– similarities between living and fossil organisms
– the diversity of life on the Galápagos Islands,
such as blue-footed boobies and giant tortoises
• Darwin became convinced that the Earth
was old and continually changing
– Concluded living things also change, or evolve
over generations
– Living species descended from earlier lifeforms: “descent with modification”
Darwin’s Journey
• Joined the H.M.S Beagle as naturalist
• Found fossils of marine animals in the mountains
• Observed many new plants and animals in S.
America
• Read Charles Lyell’s Principles of Geology -described the ancient world of plants and animals
as one in flux.
• Compared species in Galapagos with those in S.
America – must be related
• Collected much data, but didn’t publish for 20
years.
The voyage of the Beagle
Pacific
Ocean
North
America
Galápagos
Islands
Great
Britain
Europe
Atlantic
Ocean
Africa
Equator
South
America
Australia
Cape of
Good Hope
Cape Horn
Tierra del Fuego
Tasmania
New
Zealand
Alfred Russell Wallace
British naturalist
working in
Indonesia came up
independently with
a theory similar to
Darwin’s theory
The Origin of Species frontispiece
Darwin cartoon
V. Natural Selection
• Arrived at independently by Darwin
and Alfred Russell Wallace (Darwin
published first!)
• Darwin did not know about genetics
• Contrast with Lamarck, who was right
about organisms evolving from ancient
forms, but wrong about inheriting
acquired characteristics
VI. Darwin’s Theory of Evolution
by Natural Selection
• Variation exists within species
– Traits vary among individuals of the same
species
• All organisms compete for limited
natural resources
– Some will get more, some less (Thomas
Malthus)
• Organisms produce more offspring than
can survive, leads to competition
Thomas Robert Malthus
• The environment selects organisms with
beneficial traits
• Organisms with traits well suited to the
environment survive and reproduce in
greater numbers than those less well
suited. They pass these traits to their
offspring
• Darwinian fitness = an organism’s genetic
contribution to the next generation
• Over time the population becomes better
adapted to the environment
VII. Key Points
• Evolution is not the same as natural
selection: Natural Selection is the process
by which evolution occurs.
• Darwin made two main points in
The Origin of Species
– Organisms inhabiting Earth today descended
from ancestral species
– Natural selection was the mechanism for
descent with modification
VIII. Evidence of Evolution
1.
2.
3.
4.
5.
6.
Paleontology (Fossils)
Comparative anatomy/morphology
Comparative embryology
Biogeography and adaptive radiation
Direct observation of natural selection
Genetics and molecular biology
1. Paleontology or Fossil Record
• Fossils
– Are preserved remnants or impressions left
by organisms that lived in the past
– Are often found in sedimentary rocks
• Relates past organisms to living ones
• Fossil record is incomplete
Rivers bring sediment to
the
1 ocean. Sedimentary
rocks containing fossils
form on the ocean floor.
Over time, additional strata
are added, containing foss-ils from each time period.
Younger stratum with
more recent fossils
Older stratum with
older fossils
• The fossil record shows
that organisms have
appeared in a historical
sequence
As sea levels change and th
seafloor is pushed upward,
sedimentary rocks are
exposed. Erosion by rivers
reveals strata; deeper
strata contain older fossils.
The study of fossils provides strong
evidence for evolution
• Fossils and the fossil
record strongly support the
theory of evolution
– Hominid skull
– Fossil perch
– Petrified trees
and bones
– Ammonite casts
– Tracks, footprints
and impressions
– Fossilized organic
matter in a leaf
– Scorpion in amber
– “Ice Man”
• Many fossils link early extinct species
with species living today
– These fossilized hind leg bones link living
whales with their land-dwelling ancestors
2. Comparative Anatomy/morphology
• Homologous Structures
– Parts of different organisms, often
quite dissimilar, that developed
from the same ancestral body parts
Homologous Structures
• Forelimbs of the following types of organisms
are made up of the same bones but serve
different functions
– This similarity in bone structure indicates a fairly
recent common ancestor between these types of
organisms
Analogous Structures
• Wings of insects and bats serve the same
function but differ considerably in
structure and embryological development.
This indicates a remote ancestry between
these three types of organisms.
Vestigial Structures
• Organs, structures, or parts that are
incomplete or have no apparent function -remaining parts of once functioning organs.
• Examples:
– Human tail bones
– Whale leg bones
– Snake pelvic bones
– Human appendix
– Horse splint bones (ancient side toes)
Vestigial Structures
• Why do dogs have
tiny, functionless
toes on their feet?
• Ancestral dogs had
five toes on each
foot
• As they evolved they became toe-walkers
with only four toes on the ground
• Big toes and thumbs were lost or reduced
to their present state
Remnants of Toes in Horses
• Normally a horse’s
back foot has only one
functional toe, the
third
• Splints are small
remnants of toes 2
and 4 that remain as
vestiges
3. Comparative Embryology
• Early stages of vertebrate embryos
are very similar
– Gill slits
– Long tail
• Similar developmental stages may
reflect common ancestry
Embryonic History (Ontogeny)
Fish
Rabbit
Gorilla
Bioweb.cs.earlham.edu/9-12/evolution/HTML/live.html
4. Biogeography
• Study of the geographical distribution of species
• First suggested to Darwin today’s “closely allied”
organisms locally evolved from ancestral forms
• Many examples of biogeography theory support
evolution
Marsupials in Australia
Darwin’s finches on the Galapagos
Old world vs. new world monkeys
Lemurs in Madagascar
Closely allied species tend to be found on the
same continent ex. Marsupials in Australia
Australia
Koala
Kangaroo
Adaptive Radiation
• Many new species can arise from a single species
• Ex: Darwin’s finches
– On the Galapagos -- similar appearance, but
each species has a distinct beak shape and
feeding habit
– All closely related -- arose from a single type
of finch in S. America
– On the Galapagos, many different food
sources, evolved into different species
Adaptive radiation in Darwin’s finches
Adaptive radiation in Hawaiian honeycreepers
Scientists can observe natural
selection in action
• Evolutionary adaptations have been
observed in populations of birds, insects,
and many other organisms
– Example: camouflage adaptations of mantids
that live in different environments
The result of natural selection is evolutionary
adaptation
(b) A Trinidad
tree mantid that
mimics dead
leaves
(a) A flower mantid in Malaysia
(c) A leaf mantid in Costa Rica
6. Direct Observation of
Natural Selection
• Ground finches on the island of
Daphne Major in the Galapagos -“The Laboratory of Evolution”
• Artificial selection (vegetables,
domestic animals)
• Microbial resistance to antibiotics
and pesticides
• Darwin also saw that when
humans choose organisms
with specific
characteristics as
breeding stock, they are
performing the role of the
environment
– This is called artificial
selection
– Example of artificial
selection in plants: five
vegetables derived
from wild mustard
• These five canine species evolved from a
common ancestor through natural
selection
African wild
dog
Coyote
Fox
Thousands to
millions of years
of natural selection
Ancestral canine
Wolf
Jackal
– Example of artificial selection in animals: dog
breeding
German
shepherd
Yorkshire
terrier
English
springer
spaniel
Mini-dachshund
Hundreds to
thousands of years
of breeding
(artificial selection)
Ancestral dog
Golden retriever
The evolution of antibiotic resistance in
bacteria is a serious public health concern
• The excessive use of antibiotics is leading
to the evolution of antibiotic-resistant
bacteria
– Example:
Mycobacterium
tuberculosis
Insecticide application
Chromosome with
gene conferring
resistance to
insecticide
Survivors
Additional
applications of the
same insecticide
will be less
effective, and the
frequency of
resistant insects in
the population will
grow
Example of Natural selection
Industrial melanism in peppered moths (Biston
betularia) in Manchester, U. K.
1848  Carbonaria moths were at risk for
sparrow predation, speckled moths are
camouflaged against lichen covered tree trunks
1900  Speckled moths stand out in soot covered
surroundings and are at increased risk to
predation
Speckled and carbonaria forms of
peppered moths on a tree trunk
7. Genetics
• Darwin did not know about genetics
– Mendel lived during the time of Darwin,
but no evidence that Darwin was aware
of or even used Mendel’s ideas
• Modern technology gives us a deeper
understanding of the basis for Darwin’s
theory
• For example:
– Similarities in amino acid sequences
between closely related species
– Molecular biology (universality of the genetic
code, similarity in DNA sequences and
proteins of related individuals)
Human Rhesus monkey Mouse
Last common
ancestor lived
26 million years
ago (MYA),
based on
fossil evidence
Chicken
Frog
Lamprey
80 MYA
275 MYA
330 MYA
450 MYA
IX. Patterns of Evolution
• Divergent evolution
• Convergent evolution
• Co-evolution
Convergent Evolution
• Two organisms in similar environments
may appear very similar but are not
closely related
• A pattern of evolution which produces
analogous structures
• Example: fish and dolphins - streamlined
bodies
Convergent evolution in overall shape,
coloration, dorsal fin and shape of tail flukes
Convergent evolution in plants
Divergent Evolution
• A pattern of evolution in which one
species gives rise to many species that
appear different externally due to
different environments but are similar
internally
– homologous structures
• A type of adaptive radiation
Islands are living laboratories of speciation
• On the Galápagos Islands, repeated isolation and
adaptation have resulted in adaptive radiation of 14
species of Darwin’s finches
Co-evolution
• The change of two or more species in close
association with one another.
Example:
Plants and their pollinators
“Sexual Encounters of the Floral Kind”
How does variation among individuals
of the same species occur?
• Random Mutation – changes in genetic
code
• Recombination – offspring has new
genetic code formed by
recombination of codes of it parents