The Theory of Evolution
Earth’s History
The Earth was formed about 4.6
billion years ago
by 2.2 billion years ago, the Earth
probably looked like it looks today
oxygen was not believed to be in
abundant supply in Earth’s early
atmosphere
Earth’s History
oldest known cellular fossil (3.5
billion years old) traces back to a
place in Australia
- were probably cyanobacteria =
photosynthetic unicellular prokaryotes
- first prokaryotes were probably
anaerobic – Why?
Earth’s History
uniformitarianism = a principle that
states the same geographical
processes that occur today occurred
in the past
- these processes occur very
slowly, requiring organisms to change
as well (very slowly)
Uniformitariansim
Charles Darwin
Charles Darwin
did most of his research on the
Galapagos Islands
Charles Darwin
- collected 13 similar but separate
species of finches
- each had a distinct type of beak for
feeding
- overwhelming similarities showed
they came from a common ancestor
Charles Darwin
Charles Darwin
Charles Darwin
Darwin’s Theories
1) New species descend from one or a few
original types
- similar organisms arise in the same
geographic location
2) Species were modified and evolution
occurred because of natural selection =
organisms best suited for the environment
survive better (or have higher fitness) and
reproduce more successfully than others
Darwin’s Theories
3) The process of natural selection
drives evolution
4) The environment “selects” the traits
that will be increase a population
- adaptation = when an organism
becomes better suited for its
environment
Evidence of Evolution
1) Homologous Structures = similar features
that originated in a common ancestor
ex) forelimbs of a cat, whale, bat, and
human
- look different and vary in function, but
very similar in skeletal structures
- indicates they share a common
ancestor
Homologous Structures
Evidence of Evolution
2) Analogous Structures = serve
identical functions and look
somewhat alike
- ex) wing of a hummingbird and
wing of a moth
- indicates they show a remote
ancestor but evolved
independently and differently
Analogous Structures
Evidence of Evolution
3) Vestigial Structures = structures that
are found in an organism but are not
useful to them
- were useful to a common
ancestor
- ex) human tailbone, appendix,
tiny limb bones in snakes, pelvic
bones in whales
Vestigial Structures
Vestigial Structures
Vestigial Structures
Vestigial Structures
Types of Natural Selection
- a population is the smallest unit in
which evolution can occur
- bell curve = a graph that illustrates
that most members of a population
show the average form a given
measurable trait
- only a few individuals will show the
extremes of a trait
Bell Curve
Types of Natural Selection (cont)
1) Stabilizing Selection = individuals
with the average form of a trait have
higher fitness
- the most common kind of selection
- results in very similar morphology
of a species
Stabilizing Selection
Stabilizing Selection
Types of Natural Selection (cont)
2) Directional Selection =
individuals with the more extreme
form of a trait have greater fitness
than the average form
Directional Selection
Directional Selection
Types of Natural Selection (cont)
3) Disruptive Selection = individuals
with either extreme variation of a
trait have greater fitness than
individuals with the average form
Disruptive Selection
Disruptive Selection
Types of Natural Selection (cont)
4) Sexual Selection = females tend
to chose the males they mate with
based on certain traits
- the genes of successful
reproducers, rather than those of
merely successful survivors, are
amplified through natural selection
Sexual Selection
Sexual Selection
Sexual Selection
New Species
- speciation = the process of
species formation
- Speciation begins with isolation
- 2 ways for this to occur
New Species (cont)
1) Geographic Isolation = the
physical separation of members of
a population
- ex) fish in ponds in Death Valley
- fish diverged enough to be
considered separate species
Geographic Isolation – Death Valley
Geographic Isolation - Pupfish
New Species (cont)
2) Behavioral Isolation
- ex) different mating times and
calls of frogs reduce the chance
of interbreeding among the
different species
Behavioral Isolation - Frogs
Rates of Speciation
1) Gradualism = species evolve at a
steady, stable rate
2) Punctuated Equilibrium = species
arise abruptly and are quite different
from the species they came from
- seen in the fossil record where
large gaps seem to appear from one
to another
Rates of Speciation
Rates of Speciation
Rates of Speciation
Rates of Speciation
Basic Definition of Evolution
= Earth’s present day species
developed from earlier,
distinctly different species
through the process of natural
selection