Unit 3 Notes
Evolution and Adaptations
Selective Pressure
 Selective
Pressures are the factors that
cause young plants and animals in nature
to fail to survive

Examples of these include predators,
parasites, drought, lack of food, and
temperature extremes.
 Some
organisms are better equipped to
survive, by having genetic variations that
provide protection

Examples of these include traits that allow
the organism to blend in with its
surroundings, making it easier to be hidden
from predators
Selective Pressure
 Other
organisms that are lacking these
traits generally end up being the
predator’s dinner
 Some organisms have genetic traits that
may actually cause further harm to the
organism

Examples of this include if the organisms’
genes slow it down or cause its exterior
coloring to make it apparent with its
background
Natural Selection
 When
specific traits are favored to assist in
an organisms’ survival is known as natural
selection
 Charles Darwin and Alfred Russell Wallace
discovered the concepts of natural
selection.

When organisms are modified over many
generations this is called biological
evolution
Adaptations to the Environment

Selective Pressures are
constantly being
exerted on populations,
causing the gene pool
of the population to be
tested

Fitness is the ability of an
organism to adapt for
survival and
reproduction based on
the selective pressures
being exerted on the
organism
Limits of Change
1.
2.
3.
Adaptation – the population of survivors
may gradually adapt to the new
condition through natural selection
Migration – the surviving population may
migrate and find an area where
conditions are suitable
Extinction – failing the first two
possibilities, extinction is inevitable
Adaptations
 In
order for a population to successfully
adapt to the environmental conditions,
they need to have some individuals that
possess the alleles (variations of genes or
new combinations of genes) required to
survive in the new conditions.

This is not the only requirement – the
population must have enough organisms
within it that possess the alleles in order to
reproduce and carry on the population
Keys to Survival
 There
are four keys to survival for a
population
1. Geographical Distribution
2. Specialization to a given habitat or food
supply
3. Genetic Variation within the gene pool
of the species
4. The reproductive rate relative to the rate
of environmental change
Keys to Survival
 Less
vulnerable species to be affected by
changes in these keys are r-strategists
 More vulnerable species to be affected
by changes in these keys are K-strategists
 Most organisms fall in between both of
these
Genetic Change
 Genetic
change or
adaptations occur
over generations

An organism does
not adapt within its
lifetime genetically
Evolution of Species
 After
all of the adaptations that occur
over MANY generations the “final”
product may be so different from the
initial population that started the process
that it is considered a new species
 There is also a process where two or more
species are developed from one
individual species
Two Species From One
 Reproductive

Isolation
When the original population separates into
smaller populations that do not interbreed
with one another
 Separated
Subpopulations exposed to
different selective pressures

As the populations are adapted to these
pressures they begin to become so different
that they are no longer considered the
same species
Darwin’s Finches
 Charles
Darwin discovered a variation of
species of finches in the Galapagos Island


What he observed was that the different
finches had specific physical characteristics
The physical characteristics that each
species has determines its feeding habits,
making them different species.