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An Introduction to Evolution
(Main Source: University of California Museum
of Paleontology Website)
• The Definition:
Biological evolution, simply put, is descent
with modification (Darwinian evolution).
• Evolution is currently defined as a change
in the gene frequencies of a population
through generations. Evolution occurs
when population composition changes.
• Macroevolution and Microevolution
An Introduction to Evolution
• Biological
evolution is not
simply a matter of
change over time
An Introduction to Evolution
• The central idea of
biological
evolution is that all
life on Earth
shares a common
ancestor
The History of Life:
Looking at the Patterns
• The central ideas
of evolution are
that life has a
history—it has
changed over
time—and that
different species
share common
ancestors.
The Family Tree
Descent with Modification
1. Beetles on a diet
Imagine a year or two of
drought in which there are
few plants that these
beetles can eat.
All the beetles have the
same chances of survival
and reproduction, but
because of food
restrictions, the beetles in
the population are a little
smaller than the preceding
generation of beetles.
Descent with Modification
2.
Beetles of a different
color
Most of the beetles in
the population (say 90%)
have the genes for bright
green coloration and a
few of them (10%) have
a gene that makes them
more brown.
Some number of
generations later, things
have changed: brown
beetles are more
common than they used
to be and make up 70%
of the population.
Which one is an example of evolution?
Mechanisms: The Processes of
Evolution
• Mutation
• Natural selection
• Genetic Variation
as the main factor
for Evolution to
happen!
• “Founders’ effect”
• Mutations are
random.
Natural Selection
•
Imagine a
population of
beetles:
1. There is
variation in
traits.
2. There is
differential
reproduction.
3. There is
heredity.
Natural Selection
• End result:
Natural Selection at Work
Role of Fitness in Evolution
Sexual Selection and Fitness
• Sexual Selection Process (most of the
time in animals): any structural,
morphological, behavioral display of
MALES to attract FEMALES.
Male Competition and Female Choice!
Lines of Evidence: the Science of
Evolution
• James Hutton &
Gradualism
• Georges Cuvier &
Catastrophism
• Charles Lyell &
Uniformitarianism
Fossil Record
Transitional Forms (1 of 2)
Transitional Fossils (2of 2)
Homologies and Analogies
• Homology: similarity in
characteristics resulting
from a shared ancestry
• Analogy: similarity of
structure between two
species that are not
closely related;
attributable to
convergent evolution
Anatomy (1 of 2)
Anatomy (2 of 2)
Comparative Anatomy
• Modification of
tetrapod skeleton
Developmental Biology (1 of 2)
• Snakes have
legged ancestors
• Cretaceous snake
Pachyrhachis
problematicus
Developmental Biology (2 of 2)
• Baleen whales
have teeth in the
early fetal stage
and lose them
before birth
Cellular/Molecular Evidence
Artificial Selection, Ecology,
Experiments, Nested Hierarchies
1. What happened to the two
kingdoms I learned about last
year?
2. What’s the big deal about
homologies?
3. Someone told me that
Linnaeus’ classification
system isn’t accurate. Why is
that?
4.
I forgot what a clade is?
5. Why did you say birds are
tetrapods when they only
have two legs?
6. I have 3 first cousins and 2
second cousins. How can
chimpanzees be my cousins
too?
7. Should I be taking notes?
8. Would you explain the
difference between
“homologous” and
“analogous” again?