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Evolution
part I
“The process of change
over time”
Charles Darwin
Darwin is considered as the
“father” of evolution
 Losing his passion to become a
doctor in med school he took to
the sea to become a “naturalist”
in 1831

– The name of the ship he spent 5
years on was the Beagle

Darwin returned to England in
1836 with pages of notes from
what he saw as well as many
specimens from his journey
Charles Darwin

Darwin spent 36 days on
the Galapagos Islands
– These islands are located
West of the Northern part of
South America off the coast
of Ecuador
The Galapagos islands were
an undisturbed island chain
void of humans for
thousands of years
 What Darwin found
astonished him!

Charles Darwin

Because of geographic
isolation, the inhabitants
of the Galapagos evolved
without predators
– This allowed humans to get
as close as they wanted to
research the animals

Many species were the
same species he found on
other continents but, they
had key differences!
– For example, a species of
cacti normally only 5 feet
tall grew to heights of 20
feet!
And lizards swam and
ate algae
from the rocks
Charles Darwin

One of the observations
that spawned Darwin’s
curiosity was the amazing
similarities between animals
of different species!

Darwin also noticed that
plants and animals had
unique characteristics
within the same species as
well!
Important Vocabulary

Natural variation – is defined as
differences among individuals of
the same species
– Interspecific variation – is variation
among individuals of the same
species
– Intraspecific variation – variation
among individuals of different species

Artificial selection – artificial
selection is similar to selective
breeding (being “chosen”)
– An example would be the selection
for a mate that birds go through
Important Vocabulary

Adaptation – any inherited
characteristic that increases and
organism’s chance of survival
– Adaptations can be a physical
characteristic or a more complex
behavior
 This lizard is known as the Thorny Devil
and it lives in the harsh outback of
Australia where there is very little water
 To get water, it’s body has special
channels that lead water to the corners of
its mouth and all it has to do is gulp to
draw the moisture from the air that has
condensed on its body (via capillary
action)
Important Vocabulary

Natural selection – aka. Survival of
the fittest is defined as nature
“selecting” individuals with
characteristics making them well
suited to their environment
– Over time, natural selection results in
changes in the inherited characteristics
of a population. These changes increase
a species’ fitness in its environment.
–
http://www.greenexpander.com/2007/12/10/amazing-octopus-camouflage/
Genes and Variation

A group of interbreeding individuals
is known as a population
 The genome of an individual organism
is all of the genes that organism
possesses worldwide
 The gene pool is ALL of the genes in
a population including all of the
‘possible’ alleles
– For example: in Basenji puppies they
can have 1 of 4 coat colors

The relative frequency is how often
that gene occurs in the gene pool
Genes and Variation

Natural Selection and trait distribution
– Directional selection is when individuals
in a population have a higher fitness over
those in the middle range or lower range
 see figure 16-6 pg. 398
 This causes a “shift” in the fitness towards
one particular phenotype
 As an example: Suppose that there were
many different height giraffes in a region of
Africa that underwent sever climatic change
 The food availability is now 8’ higher than
before and only a limited number of giraffe
can actually reach the resource
 This would be directional selection
Natural Selection in Populations

In any population of
organisms there is
variation within the
species
– There are organisms
that fit into a “bell
These are two bell curves
curve” whereby the
shown above. The mean is
largest percent of the the average and the majority of
population is in the
the population phenotype. The
center with slightly
curve represents the entire
different variations on variation within the population
either side
Directional Selection

Directional selection
– is the effect of a shift
in a population’s
phenotype in response
to natural selection
towards a more
favored phenotype
from the variation
within the original
population
Disruptive Selection

Disruptive selection
– Occurs when both
extreme phenotypes
are favored by natural
selection while the
mean population is
selected against by
something in nature
Stabilizing Selection

Stabilizing selection
– Occurs when the mean
phenotype is highly favored
in the environment and
becomes even more
dominant in the population
– This can lead to a lower
diversity which makes
species susceptible to
disease or other limiting
factors