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Origin of Life
Theories of Evolution

Lamark’s Explanation
a. believed that traits were
“acquired” and not
determined by genes
b. traits were results from
organisms experiences or
behavior
c. “necks of giraffes”
Charles Darwin’s
Theory of Evolution
 Galapagos
Islands
a. Darwin’s finches
 Origin
of Species by Natural
Selection – by Charles Darwin
 Evolution
– concept that species
have changed over time
Natural Selection
“organisms best suited to their environment
reproduce more successfully than other
organisms”
1. Adaptation
2. Fitness
-competition
*selection conditions change as the demands
of the environment change
*if environmental change is too extreme,
populations cannot adapt quickly enough
and they become extinct
Patterns of Evolution


Genetic Drift – the alteration of allele
frequencies by chance events
Punctuated Equilibrium – speciation occurs
during brief periods of rapid genetic change



Divergent Evolution – two or more
related populations or species become
more and more dissimilar
- domestic dogs
Convergent Evolution – 2 organisms
seem to be similar but are not at all
- shark and porpoise
Co-Evolution – 2 species evolve together
- plants and the animals that pollinate
them
Evidence of
Evolution
Evidence from Living
Organisms
Homologous and
Analogous
Structures
a. Homologous –
similar features that
originated in a
shared ancestor

b. Analogousfeatures serve
identical functions
and look somewhat
alike
 Vestigial
Organs
“useless features”
a. appendix
b. human tailbone
 DNA
and Chemical Studies
a. human and chimp DNA – very
similar
 Embryo
studies
a. all vertebrae embryos are similar
at 4 weeks
b. all vertebrates have gill slits at 4
weeks
Types of Natural Selection



Stabilizing Selection
* individuals with average form of a trait have
the highest fitness
 most common
Directional Selection
* individuals that display a more extreme form of
a trait have greater fitness than individuals with
an average form of trait
Disruptive Selection
* individuals with either extreme variation of a
trait have greater fitness than individuals with
the average form of the trait