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How do we know about past
life on Earth?
Fossils- any evidence
of prehistoric life, not
necessarily just the
remains of plants and
animals. Found most
often in: ice, tar,
amber, casts,
imprints, and
petrification.

How do we know about past
life on Earth?
Examples
include: Bones,
Shells, Trails,
Footprints,
Burrows of
Worms, Seeds,
and even Spores
of Fungi

You’re how old?...Dating
Fossils
Relative
Datingdetermined
by the depth
or position in
the soil.

You’re how old?...Dating
Fossils
Absolute
dating- using a
radioisotope
and half-life to
determine the
rocks age

Half-life: the length of time it takes for half
the radio-active atoms in a given sample to
decay.
Evidence for
Evolution
Patterns of common
descent are seen in
classification.
 Internal similarities:
 Comparative: anatomy,
biochemistry,
embryology, DNA
sequencing, fossil
remains, convergent
evolution, divergent
evolution



More Evidence for
Evolution
Vestigial organs: are
remnants of onceuseful parts.
Homologous
Structures: structures
that have different
mature forms in
different organisms,
but develop from the
same embryonic
tissues.
Even More Evidence

Fossils
Evolution Theory
Contributors

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
Hutton- Earth and life
are gradually
changing.
Malthus- organisms
are producing more
and faster then the
number dying.
Lyell- Earth is very
old.
Cuvier- organisms
died as a result of
catastrophic disasters
Evolution Theory
Contributors


Wallace- has same
ideas as Darwin,
doesn’t rush to
publish…validates
Darwin’s work
Lamarck- theory of
acquired
characteristics
(environmental
pressures and
internal desires
bring on changes in
the body).
Lamarck example:


EX. Giraffes necks
grew longer as
they tried to get
food higher in the
trees.
Didn’t take into
consideration that
those with longer
necks had an
advantage.

The more an
organism used a More
specific body part,
the better chances
the offspring would
get this feature or
trait.

Ex. A weight lifter,
because the parent
was large due to
lifting weights, the
offspring would be
large too.
on Lamarck
Our Main Man…Charles Darwin
Darwin was a
naturalist and took a
trip on the HMS
Beagle- around the
world in 5 years!
Found a wide variety
of organisms and
stated: Change is
inevitable over a
period of time.
So….What is Evolution?
Evolutiongenetic change
over a period of
time
Populations,
NOT individuals
evolve through
mutations and
genetic
variations


Darwin referred to evolution
as: descent with
modifications:
each living species has
descended with changes
from other species over time


Adaptations:
physical and
behavioral traits
that allow and
enable organisms
to survive.
Fitness: ability of
an organism to
survive and
reproduce.
(Passing genes to
offspring.)
Trends
All living species tend to
over-produce
 Most seeds, eggs, or
hatchlings die before
they can reproduce
 All living species are
extremely variable
 Many variations are
inherited.

Selection in
Nature…
Individuals of the same species are
different: some have slight advantages or
disadvantages in the struggle for
existence.

Selection in
Nature…

Struggle for existence- high birth
rates and shortage of life’s basic
needs forced organisms into a
constant struggle for existence.
Competition!
The fastest predators could catch the
most prey
 The best camouflaged, protected or
fastest prey survived the hunt.

Selection in Nature…
Natural Selection- generation after
generation the fittest individuals
survive in nature. This explains
how well-suited species become
better suited to their environment
as they respond to the various
selection pressures.

Evidence for Natural Selection


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All living things are highly adapted to
their way of life.
Many adaptations cannot be explained
by environmental influence.
Some adaptations are less than perfect.
NS has been observed and has resulted
in changes in natural populations.
Artificial selection by “breeders” has
produced many new adaptations
No two
alike….

Farmers told Darwin that no 2
individuals (plants or animals) were
alike, some were larger, smaller,
lighter, heavier, produced more milk,
produced larger fruit, etc…. They
knew that the traits were inheritable
(Mendel), and they also knew what
to do with these individuals when
they found them…
No two alike….


Farmers would look over their stock
and decide what characteristics they
wanted to see in the next
generation…they would select them….
Artificial Selection- allow only certain
organisms to reproduce to obtain
certain results (characteristics) in
offspring.
Darwin’s Finches

On the Galapagos Islands,
Darwin found many different
birds that were seed eaters
with different beaks. Darwin
found out, after some
observations, that all the birds
were not different species, but
all Finches.
Darwin’s Finches

The finches (no matter how different
they looked) all evolved to have
different beaks so that they could all
survive on the island by maximizing
food resources. (If they all ate the
same seeds, there would be a food
shortage so over time some took to
eating fruit, insects, seeds…. They
could all survive.)
Evolution of a Species



Species are evolutionary units in which
gene flow occurs.
Natural populations belong to the same
species if they can interbreed and leave
fertile offspring.
Most new species originate geographically
when interbreeding populations are
isolated for long periods of time and the
gene pool remains within the group of that
habitat.
Reproductive Isolating Mechanisms
1. Ecological isolation occurs when
potential mates do not meet because they
are in different habitats.

Reproductive Isolating Mechanisms
2. Seasonal isolation is when potential
mates breed at different seasons or at
different times.

Reproductive Isolating Mechanisms
3. Behavioral isolation might occur when
mating courtship is different.

Reproductive Isolating Mechanisms
4. Mechanical isolation occurs when the
reproductive structures do not match up
properly.

Genetic Drift
Migration- the movement of organisms
through a geographical area.

Immigration- INTO a geographical area
 Emigration- OUT OF a geographical area

Genetic Drift
Directional movement- a shift in a
population to 1 side; either the right or
the left

Genetic Drift
Disruptive movement- a shift in a
population to both ends decreasing the
number in the middle.

Genetic Drift
Stabilizing movement- a balancing out of
populations evenly through the species.

Natural Selection may be
Disturbed by Man
Destroying natural
habitats
Endangered species
Extinct species



Scientists
estimate that
between 5 and
50 million
different species
make the Earth
home.
Remember: a
species is a
group of
organisms able
to reproduce
viable offspring


Scientists
estimate that
99.9% of all
species that
have ever lived
are now extinct.
How do we
survive?
The Problem of
Reproduction

Back to Malthus- 1788, observed that
babies were being born faster than
people were dying. If this continued,
the world would be overrun by
humans. So Malthus suggested that
war, famine, and disease would limit
the human population (stress on the
environment)
Why evolution…
In relating evolution to physics,
everyone knows that gravity works
although it is very hard to
understand why it does, the same
goes w/ evolution and biology.
Evolution explains why bacteria
become resistant to antibiotics, and
why insects become resistant to
pesticides.

Why evolution…
Inheritable variation (through
evolution) is essential to species
survival.
