Download Natural Selection

Organic Evolution
A change in allele frequencies in a
population or species.
Story of the Peppered Moth

Dark form dominates
after pollution kills
lichen.
Changes in allele frequencies in
populations can occur because
of:
Mutations (increases genetic diversity)
 Genetic Drift (chance, particularly in
smaller populations)
 Migrations
 Natural Selection (decreases genetic
diversity)

Or Natural Selection
Theory of Natural Selection
1.
2.
3.
Since more babies are born than an area can
support, many die before reaching reproductive
age.
Individuals in a population differ. Some of this
variation is heritable.
Individuals with heritable variations that increase
their chance of reproductive success will make a
greater contribution to future generations. So the
characteristics of individuals in subsequent
generations will change.
What are they contributing?
Do the above processes cause
either or both of these to occur?

Microevolution = The
small genetic changes
a population
undergoes.

Macroevolution =
Long-term, large scale
evolutionary changes
among groups of
species (includes
speciation)
Review: Mechanisms of
Evolution
Mutations- change in the DNA sequence.
 Genetic drift- random change in the allelic
frequencies of a population.
 Migration/Immigration- genetic exchanges
with another population.
 Natural Selection- differential reproductive
success of genotypes.

Natural Selection

The differential action of environmental
factors operate on the inherited variability
of a population or species tending to
eliminate those individuals which are less
fit.
Fitness or Ecological Fitness
The reproductive advantage of an
individual in a population
under a given set of
environmental conditions.
How does Natural Selection
work?
Case 1: Stabilizing Selection.
Case 2: Directional Selection.
Case 3 : Disruptive Selection.
Natural Selection (cont.)
Suppose there is a population of rabbits. The color of the rabbits
is governed by two incompletely dominant traits: black fur represented
by “B” and white fur represented by “b”. A genotype of “Bb” would
have gray fur (a display of blended black and white).
If this population of rabbits were put into an area that had very
dark black rocks as well as very white colored stone, the rabbits with
black fur would be able to hide from predators amongst the black rocks
and the white furred rabbits would be able to hide in the white rocks, but
the gray furred rabbits would stand out in both of the habitats and thus
would not survive. This environment selects for the two extremes and
against the middle.
What type of selection is this??
Speciation
The creation of two separate species
from 1 original species
How does Natural Selection
work?
Case 1: Stabilizing Selection.
 Is
this likely to lead to speciation?
How does Natural Selection
work?
Case 2: Directional
Selection.
 Is
this likely to lead to speciation?
How does Natural Selection
work?
Case 3: Disruptive Selection
 Could
this lead to speciation?
Sympatric Speciation
“Same land” - speciation
Sympatric Speciation
Allopatric Speciation
“Different lands” - Speciation
Allopatric Speciation
Allopatric Speciation
Kaibab
Squirrel
Abert’s
Squirrel
Tortoises (Gopherus)
Desert Tortoise
Gopher Tortoise
Texas Tortoise
Diamondbacks (Crotalus)
Western
Diamondback
Rattlesnake
Red Diamondback Rattlesnake
Eastern Diamondback Rattlesnake
Some Types of Evolution
Divergent Evolution
Some Types of Evolution
Convergent Evolution
Green Tree Python
Emerald
Tree Boa
Convergent Evolution
(cont.)
Convergent Evolution
(cont.)
Some Types of Evolution