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Zoology
Unit 2
Evolution – the change in a
population over time.

Pre-Darwin Ideas
1. Lamarck
A. French zoologist
Thought organisms developed
new organs or modified
existing organs to adapt to
new situations.
 Organs not used would
degenerate.

Species did not become
extinct, only evolved into new
species.
 Giraffes – Thought they got
long necks by stretching to
get to higher leaves.

Wrong because modifications
like that cannot be passed to
the next generation.

2.
Darwin’s Ideas
A. Thought species changed
over long periods of time. (too
long)
B.
Theory of
Uniformitarianism (Charles
Lyell) said the earth was very
old and the earth changed
over time. This idea
reinforced Darwin’s idea.
C.
From looking at fossils on
South America he recognized
that some animals become
extinct without leaving
descendents or becoming new
species.
D.
On Galapagos he observed
finches and tortoises.
E. The finches have different
size beaks with different
shapes. Depending on what
they eat. They show
“adaptive radiation”.
Adaptive
radiation is the
formation of new forms of a
species from an ancestral
species in response to the
opening of new habitats.
F. Natural selection –
developed after reading
Thomas Malthus. He said
human population will continue
to grow until stopped by some
factor such as war, famine,
disease, etc.
Darwin
thought the same
thing might happen in nature.
G.
Natural Selection has 4
parts.
1. All organisms produce more
offspring than can reproduce.
2.
Inherited variation exists.
Variations come from
mutations in DNA and random
mating. Some may be
advantageous, some may be
harmful.
3.
Individuals with the
advantageous traits are more
likely to survive and pass
them to the next generation.
These are called adaptive
traits.
4.
Adaptive traits are passed
on and become more
frequently seen in the
population. Traits that are
dis-advantageous to the
individual will eventually be
eliminated.
3.
MICRO and MACRO
EVOLUTION
A. Microevolution is a
change in the frequency of
alleles in a population over
time.
Examples
are drug resistant
strains of bacteria and bug
that are resistant to
pesticides.
B.
Macroevolution is the large
scale changes that result in
extinction and the formation
of new species.
C.
What scientists refer to
as evidence for
macroevolution.
1. Biogeography is the study
of the geographic distribution
of plants and animals.
Biogeographers
try to explain:
Why similar animals end up in
places that are not connected
physically. Ex. – cats
Why
animals separated by
geographical barriers are
often very different in spite
of similar environmental
conditions. Ex – Australia and
New Zealand.
2.
Paleontology – the study of
fossil records. Older fossils
are usually found below or
deeper than new fossils. By
looking at how fossils change
from older layers to newer
layers we see how animals
have changed.
3.
Comparative Anatomy
Convergent evolution occurs
when we find superficially
similar structures in
unrelated organisms.
Ex – wings in birds and
insects.
In
this case
the wings are
said to be
analogous
structures.
Comparative anatomy is the
study of living and fossilized
animals and their
relationships.
In
comparative anatomy
homologous structures are
studied. These are structures
in different animals that
suggests they have a common
ancestor.
Ex.
bones in the forelimbs of
birds, humans, lizards, bats,
etc. as seen in figure 4.11 on
page 62.
Homologous
DNA molecules –
related animals have similar
DNA derived from the
ancestral DNA.
4.
Developmental Patterns
By looking at early embryonic
stages we can see similarities.
From the embryonic stage
organisms begin to develop
differently.
This
is due to genes that
control how fast the bones
and organs develop and how
they are proportioned.
Phylogeny
– Scientists use
evolutionary evidence to build
a phylogentic tree. Phylogeny
refers to the evolutionary
relationships of modern
descendents of a common
ancestor.
The
tree shows the
relationship between
organisms, the branches show
where species diverged into
separate species.
A.
Population 6+
and Gene Pool
1. A population is a group of
individuals of the SAME
species that occupy an area
at the same time.
Within
the population the
individuals will all have the
same kind of genes.
Differences seen in individuals
is due to the presence of
different alleles.
All
the alleles for traits in all
traits in a population is called
the gene pool. It is a pool of
hereditary resources
containing all the possible
alleles an individual can be
made from.
2.
Population genetics is the
study of the genetic events in
the gene pool. The HardyWeinberg theorem describes
what happens to the
frequency of alleles in a
population over time.
The
Hardy-Weinberg theorem
says if certain things
(assumptions) are met no
evolution will take place and
the frequency of alleles will
not change in future
generations.
What
are these assumptions
that must be met to prevent
evolution? There are four.
First
– The population size
must be large.
Second – Mating between
individuals must be random.
Natural selection must take
place.
Third
– Individuals cannot
move into or out of the
population. This keeps new
alleles from entering the gene
pool.
Fourth
– No new types of
alleles are introduced due to
mutation.
It
is very unusual for all
these assumptions to be met
so most populations are
evolving.
B.
Evolutionary Mechanisms
Things that can happen
when the Hardy-Weinberg
assumptions are not met.
1.
Sometimes individuals
meet and reproduce by
chance. No natural selection
is involved.
When
this changes the
frequency of alleles in a
population it is called “genetic
drift” .
2.
Genetic drift is most
likely to occur in small
populations.
3.
The Founder Effect is an
example of genetic drift. This
occurs when a very few
individuals from a large
population colonize a new
environment away from the
parent population.
The
new colony will only
contain the genetic make-up
of the individuals that
founded the new colony.
4.
Another type of genetic
drift is the Bottleneck
Effect. This occurs when an
event drastically reduces the
size of a population.
The
remaining population may
grow to its original size but it
will not have the same genetic
diversity.
C
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Most
biologist believe genetic
diversity is important to a
species survivability. This is
because a population with high
genetic diversity will allow it
to survive environmental
changes.
5.
Gene Flow – The HardyWeinberg theorem assumes no
immigration or emigration. If
it does occur there will be a
change in the number of
alleles and the kinds of alleles
in a population.
6.
Mutation – mutations are
the origin of new alleles and
variations. These may help
the organism become better
adapted to their environment.
Or not.
C.
SPECIES AND
SPECIATION
1. A species is a group of
populations in which genes are
actually or potentially
exchanged through successful
interbreeding.
2.
Speciation is the formation
of new species. This can
occur in different ways such a
reproductive isolation.
C.
Rates of Evolution
1. Phylogentic gradualism – in
this model changes are
gradual over long periods of
time.
2.
Punctuated equilibrium – in
this model there are long
periods of stasis then rapid
periods of change. The
sudden and rapid change may
be due to environmental
changes (like climate change).