Download 15-1 The Puzzle of Life*s Diversity

Darwin's Theory of Evolution
Textbook pages 274-292
Charles Darwin
• Charles Darwin, Alfred
Wallace and others promoted
the idea of evolution as they
tried to make sense of the
following question:
“How could there be so many
different kinds of living things
(diversity) and at the same
time how can all living things
be so similar (unity)?
Charles Darwin
• given credit for the Theory of Evolution
• provided evidence for the theory
– “On The Origin Of Species By Natural Selection”
• made his observations and collected his
evidence during a five year trip around the
world on the H.M.S. Beagle
Galapagos Islands
• stop that influenced
Darwin the most
Galapagos Islands
• Of all of the stops Darwin
Made the one that
influenced him the most
was a small group of
islands called the
Galapagos Islands. He
noted that the
characteristics of many
plants and animals varied
considerably from one
island to the next.
Evolution
• change in a gene pool over time
The Five Fingers of Evolution
The Five Fingers (causes) of Evolution
1.
2.
3.
4.
5.
Small Population
Non-random mating
Mutations
Gene Flow
Natural Selection
1. Small Population
• chance can have a large effect on a small
population
– unlikely events can occur when a gene pool is
small
1. Small Population
• Genetic Drift
– In small populations, individuals that carry
a particular allele may leave more
descendants than other individuals, just by
chance. Over time a series of chance
occurrences of this type can cause an
allele to become common in a population.
• Remember genetics is controlled by the laws of
probability
• Remember with small populations we may not get what
is expected (deviation may be high)
1. Small Population
• Founder effect
– Loss of genetic variation when a new population is
started by a small number of individuals
2. Non-random Mating
• Mating amongst individuals in a population is
not always random
• Sexual Selection
– some features do not have a function that help
individuals survive, but help them have more
offspring
3. Mutations
• changes in genetic material
• can add new genes to a gene pool
4. Gene Flow
• movement of genes due to immigration and
emigration
5. Natural Selection
• Individuals that have physical or behavioral
traits that better suit their environment are
more likely to reproduce more successfully
than those without those traits.
5. Natural Selection
• Fitness
– the ability of an individual to survive and
reproduce
– an organism’s fitness is the result of adaptations
• inherited traits or variations that increase the
individuals chances for survival
• Darwin said organisms which are best
adapted (fit) for the environment are the
ones that survive
– survival of the fittest
Adaptation Example
• Darwin’s Finches
– Adaptations
• beak size
– Improved Change for Survival
• being able to eat available food sources
Darwin’s Theory of Evolution
1. Inherited variation exists within the genes of
every population because of mutations and
translation errors.
2. In a particular environment, some
individuals of a population are better suited
to survive (because of variation) & have
more offspring (natural selection).
Darwin’s Theory of Evolution
3. Over time, the traits that make certain
individuals of a population survive &
reproduce tend to spread in that population
4. Overwhelming evidence from fossils that
living species evolved from organisms that
are extinct.
The Five Fingers of Evolution