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Change Over Time
What is the Theory of Evolution?
(1) All life forms on earth
developed from earlier forms.
(2) All still living species continue to
evolve today.
Two Types of Evolution
Microevolution—on a
small scale, creating
changes in a population like
we will see in Gizmos
Macroevolution—on a big
scale, forming totally new
types of organisms
Mechanism of Evolution
How does it work? There are several mechanisms that have
been suggested.
The easiest mechanism to understand is Natural Selection.
1. More organisms are produced than can survive.
2. Natural variation among individuals is
genetically controlled.
Different phenotypes in a species
3. Some individuals better adapted (fitter). They
live longer and produce more babies.
More “fit” organisms have better chance for
survival, as in the well-known phrase
"survival of the fittest".
Modern scientific definition of fitness is not
how long an organism lives, but how
successful it is at reproducing.
Fitness, cont.
Organism A: Lives 5 years
Produces 120 offspring
Organism B: Lives 10 years
Produces 60 offspring
Which is fitter?
4. The population changes as
more have that trait.