Theories of Evolution
Chapter 15
Part I
Definition of Evolution:
• A heritable change in the characteristics within a
population from one generation to the next.
• “Change over time.”
• How does this happen?
Just So Stories
• How The Peacock Got its Tail
• Why Sex?
Ideas of Darwin’s Time (1800’s)
1. Curvier: studied rock strata and found that deeper
rocks contained extinct life forms that became
increasing different.
 Catastrophism- sudden geologic catastrophes that
caused mass extinctions in the past
2. Lyell: the geologic process that shaped the Earth’s
surface still occur today
 Uniformitarianism
3. Jean Lamarck
 Life can arise from nonliving matter
 Simple life forms change over time
Inheritance of Acquired Characteristics: Organisms can acquire
traits during their lifetime as a result of experience or
behavior and can pass these traits on the future
generations.
Examples:
• Webbed foot = stretching of membrane between toes
• Long Necks = from stretching to get food
Darwin & Wallace’s Theory (1858)
• Theory of Natural Selection: Organisms best suited to
their environment reproduce more successfully than other
organisms.
• “Survival of the fittest”
Lamarck versus Darwin:
Charles Darwin
• Voyage of the HMS Beagle
• Published: On the Origin of Species by Means of Natural
Selection
• Goals: present evidence that evolution occurs and
explain the variety and distribution of organisms
Darwin’s Observations:
• 13 Similar but separate species of finches
– Different bill specialized for food source
• Overwhelming similarities lead to the belief of a
common ancestor
Darwin’s Conclusions:
1. All species are engaged in a struggle to survive
in their changing environment.
2. Species change through continual
modifications.
3. Modifications that are best suited for the
environment are preserved.
4. All species descended from one or a few
original types of life (controversial!)
Modification by Natural Selection
• Mechanism by which evolution occurs
• Environment limits growth of populations
– Overproduction: each species produces more
offspring than can survive to maturity
– Darwin used work of Thomas Malthus on human
overpopulation to make conclusions about nature
• Genetic Variation: Not all individuals in a
population are identical, thus the environment
will affect individuals differently in a population
• Individuals with favorable traits will reproduce
more often and in higher numbers than
individuals with unfavorable traits.
Adaptation
• An inherited trait that increases an organism’s chance
of survival in a particular environment
• “Adaptive Advantage”
Fitness:
• a measurement of the ability of a species to
respond to the pressures of natural selection
• The ability of individuals to survive to propagate
their genes
• “Survival of the Fittest”
Lamarck Reading
1. What is the role of the environment in
Lamarck’s explanation?
2. What scientific approach is suggested by
Lamarck’s statement: “Nothing of all this can
be considered as hypothesis or private opinion;
on the contrary, they are truths which, in order
to be made clear, only require attention and
the observation of facts.”
Lamarck cont.
3. Was Lamarck’s explanation scientific? Why or
why not?
4. Can you propose any other explanations for
Lamarck’s observations about the disuse and use
of organs?
Darwin Video
• Who was Charles Darwin?