THE THEORY OF
EVOLUTION
Evolution – changes in a population over time
• Microevolution
• Small changes over SHORT periods of time
• Supports improvements in existing species
• Macroevolution
• Small changes accumulating over LONG periods of
time result in major changes
• Supports the formation of new species
3 types of evolution:
1.Divergent –
similar organisms
become increasingly
different because of
different types of
environments
2. Convergent different organisms
become increasingly
similar because of
similar types of
environments
3 types of evolution:
3. Coevolution two nonrelated species
change because of the
close interaction
ex. predator/prey
ex. plant/pollinator
Cladogram
• Diagram showing evolutionary relationships based
on similar characteristics
• Usually shows divergent evolution
Which are more
related?
crocs and rabbits
or
crocs and birds
Which organism is the
most “primitive”
(evolved earliest)?
What causes evolution to happen?
NATURAL SELECTION***
(“survival of the fittest”)
Development of the
Natural Selection Theory
•1700s – Lamarck was the
first person to state that
organisms change over
time and that new
organisms are modified
descendants of older
organisms (with his theory
of acquired traits)
Development of the
Natural Selection Theory
• 1800s – Charles Darwin sailed on the H.M.S. Beagle
and gathered data from organisms (fossils, finches,
etc.)
•From this data,
Darwin inferred that
all species had
descended from one
or a few original types
of life
•Darwin also
concluded that the
way
species/organisms
change over time was
by natural selection
The Process of Natural Selection
There must be variation in the traits of a
population. (This variation is caused by
organisms having different genes.)
The Process of Natural Selection
There must be environmental pressures
that favor one variation of the trait over
the other.
The Process of Natural Selection
•Organisms with the better traits will survive
better and longer, reproduce, and pass those
good traits on to their offspring.
The result will be
a population
better suited for
the environment.
What causes evolution to happen?
Geographic isolation
•
organisms of a population
can become isolated from
one another by a geographic
barrier
•
if they are no longer able to
reproduce, they may become
two separate species
•
the formation of a new
species is called speciation
What causes evolution to happen?
Artificial Selection
• Humans cause evolution to
happen because we
“choose” which traits to
select for
• Examples:
• Breeding dogs to have
desirable traits
• Genetic engineering