Download Evolution – Just A Theory?

Evolution
The Theory of Evolution

The term theory in colloquial use is closer to the
concept of a “hypothesis” in science (an educated
guess or hunch).

In science, a theory  hypothesis. A Theory is more
comprehensive than a hypothesis.

National Academy of Science:
“a well-substantiated explanation of some aspect of
the natural world that can incorporate facts, laws,
inferences, and tested hypotheses.”
Who’s the man?
 Charles Darwin
 Born 1809, 5th son
of wealthy physician

Studied medicine
and natural history
in Edinburgh

Studied to be a
clergyman at
Cambridge
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.
Charles Darwin’s 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’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.
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.
Does Darwin’s 2nd part still apply to
humans?

Many
countries are
prime
examples of
overpopulation
Darwin’s Theory
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.
Adaptation
Great moments in evolution
Adaptation
Preying mantis
camouflage
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 + 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’s 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’s Theory of Evolution
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?
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.