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Evolution – Just A Theory?
Evolution in the News
• 1925: Scopes “Monkey” Trial
― science teacher charged with contravening Tennessee’s Butler
Act, which forbade the teaching of "any theory that denies
the story of the Divine Creation of man as taught in the
Bible, and to teach instead that man has descended from a
lower order of animals."
• 1980s: Alabama and Louisiana laws mandating teaching of
“creation science” found to be unconstitutional
• Right now: Challenges to teaching of evolutionary theory
versus “Intelligent Design” in Kansas, Michigan,
Pennsylvania (aclupa.blogspot.com)
Charles Darwin
• Born 1809, 5th son of wealthy
physician
• Studied medicine and natural
history in Edinburgh
• Studied to be a clergyman at
Cambridge
Charles Darwin’s Controversial Theory
• Charles Darwin – 19th century scientist
• Famous for Theory of Natural Selection
― In a population, naturally occurring variations
affect which individuals survive and
reproduce
― Natural selection - the force which acts on
populations, and the best adapted organisms
survive
― Evolution - the process by which populations
change over time
• Darwin rarely used the word “evolution” so as not to
imply progress in a certain direction or towards a set goal
Charles Darwin’s Controversial Theory
150 years of controversy!
Competing Belief
• Many people, even today, do not believe in the theory of evolution,
but instead, the idea of creationism.
• Creationism is static and unchanging… but has meaning and purpose.
What is a Scientific Theory?
• National Academy of Science:
“a well-substantiated explanation of some aspect of the
natural world that can incorporate facts, laws,
inferences, and tested hypotheses.”
• Modern science is based on the scientific method
Darwin’s theory
• Darwin published his findings from his trip
around the southern hemisphere in a book called
On the Origin of Species
― Darwin visited the Galapagos Islands, a group of very small
islands off the coast of Ecuador.
― Even though the islands are close together, each island has a
unique climate.
• Darwin proposed that evolution worked by way
of natural selection.
Charles Darwin – Voyage of the Beagle
• 1831: Joined the HMS Beagle on five year voyage to South
America
― Studied geology, paleontology, plants and animals
Animals of the Galapagos
Darwin could tell by the shape of the Giant
Tortoises’ shells and their neck length
which island they were from.
Darwin’s theory
1. Organisms differ, and some of this variation is
heritable.
― Some cows produce more milk, some apple trees produce
larger apples, etc.
― People now use artificial selection: nature provides the
variation, but humans select for the variations they find
useful
― Ex. Only breed the dogs that lose the least amount of fur.
Darwin’s theory
2. Organisms produce more offspring than can
survive, and many that do survive do not
reproduce.
3. Because more organisms are produced than can
survive, they compete for limited resources.
― Struggle for existence.
― In this struggle, predators that are faster get more prey.
Darwin’s theory
4. Natural selection causes species to change over
time.
― Survival of the fittest!!! (natural selection)
― Adaptation is any inherited characteristic that increases an
organism’s chance for survivial.
― Those individuals best adapted to their environment will
survive and reproduce.
Darwin’s theory
5. Species alive today are descended with
modification from ancestral species that lived in
the distant past.
• All living organisms are
Related to one anothercommon descent.
• Single “tree of life” links
all living things (classification)
Darwin’s Finches
• Finches looked different on
different islands
• Different beak shapes
depending on feeding habits
• Finches on different islands
can still interbreed but
geographically isolated
― in the process of becoming
different species
Evolution by Natural Selection
• Natural selection - force of nature that acts on populations
― Individuals that compete more effectively pass on their traits to the
next generation
• Natural variation plus natural selection = evolution
• All species could share common ancestor
Evidence of Evolution
1. Molecular Evidence
• Study proteins (amino acid sequences)
• Biologists believe that the greater the similarity between the amino
acid sequences of two organisms, the closer their relationship
2. Fossils
― Fossil evidence can show us what older, possibly extinct organisms
looked like and we can compare them to organisms known today.
3. Homologous Structures
― Similar bone structure can reveal evidence of evolutionary
relationships.
4. Comparative Embryology
― The more similar organisms are in their embryological
development, the more closely they are related.
Molecular Evidence
•The more amino acids that are
the same, the closer the
evolutionary relationship
between the organisms.
•Hemoglobin, protein in blood,
is often looked at for
comparisons – all of these
organisms have blood.
Fossils
• Radioactive dating gives
relatively exact dates for fossils.
•If undisturbed, the older fossils
will be found deeper in the ground
than younger fossils.
Homologous Structures
• Homologous structures:
― Structures have different
mature forms , but from the
same type of tissue.
― Suggests common
ancestor.
• Analogous structures:
― Similar in function, but
not from the same ancestor.
Embryology
• Embryological development
• The developing embryos of many
very different organisms are
surprisingly similar in their early
stages.
Ideas that Shaped Darwin’s Theory
• At the time Darwin
•
was doing his
research, the majority
of people in the world
though that the earth
was only a few
thousand years old.
5 main scientists
helped shape our
modern theory of
evolution.
Classification of Species
• Carl Linnaeus (1700s)
― Identify relationships between groups of organisms
― Species: groups of organisms based on physical
resemblances and ability to interbreed
― Created system of classification - taxonomy
Family
Genus
Species
Common name
Canis
familiaris
Dog
Canis
lupus
Wolf
Vulpes
vulpes
European fox
Vulpes
fulva
American fox
Canidae
How old is the earth?
•James Hutton and Charles Lyell, both geologists, helped
scientists realize that the earth is many millions of years
old.
• Contrary to popular religious beliefs at the time.
James Hutton
Charles Lyell
Lamarck – Theory of Evolution
• Jean-Baptiste Lamarck – French
naturalist
• By the use or disuse of organs,
organisms acquired or lost
certain traits during their
lifetime.
• Organisms pass on acquired
characteristics to next
generation
• Organisms adapt to different
environments, causing
branching of species
― “Use it or lose it”
Lamarck – Theory of Evolution
But how are species selected in nature?
• Insight from Thomas Malthus: struggle for existence
― Constant pressure of expanding population for resources
• If the population keeps growing unchecked, humans would
run out of living space and food (1798).
• He felt the only thing that could limit population growth
would be war, famine and disease.
― Was he correct?
Darwin’s Career
• 1858: Alfred Wallace published a similar theory to
•
Darwin’s
1859: Darwin published The Origin of Species by Means
of Natural Selection, or The Preservation of Favoured
Races in the Struggle for Life
• Darwin dubbed “most dangerous man in England” but
became famous and well-respected scientist
• Later published The Descent of Man and Selection in
Relation to Sex and The Expression of the Emotions in
Man and Animals
Major Misconception about Evolution
Evolution has never
been observed.
• Peppered moths during
industrial revolution.
• Change has been directly
observed.
― Antibiotic Resistance
― Flu Vaccines
• Creation of new species of
bacteria has been directly
observed.