Download Evolution

Evolution
Evolution
• Change in a
population of
organisms over
time.
• Cladogram – a
chart that shows
an organism’s
evolutionary
history
Theories of Evolution
• Jean-Baptiste
Lamarck – 1809
published his theory
of evolution
– Mechanism of
Evolution =
Inheritance of
Acquired
Characteristics
Theories of Evolution
• Charles Darwin – 1859
published his theory of
evolution in the major
work, On the Origin of
Species
– Mechanism of Evolution
= Natural Selection
Lamarck’s Ideas
• Organisms change over time
• Organisms are adapted to their
environment
• All organisms are continually changing
and acquiring features more suitable for
their environment.
Larmarck’s
Legless
lizard: NoteIdeas
ear hole.
Snakes do not have ears.
• During an organism's lifetime, there is
selective use or disuse of its organs
and traits. (Example: Lizard living in
burrow…)
• These acquired traits can then be passed
on to their offspring. Over time, this
process leads evolution of the species.
Comparison of Lamarck’s and
Darwin’s Ideas on Evolution
Lamarck
• Short necked
herbivore lives in
savanna
• Grasses are available
to the animals. Trees
leaves are out of
reach of most of them
• Animals are adapted
to their environment.
Darwin
• Same
• Same
• Same
Comparison of Lamarck’s and
Darwin’s Ideas on Evolution
Lamarck
• The animals stretch
their necks to reach
the leaves on the
trees. Continued
stretching causes an
elongation of necks.
• The animals
reproduce. The
young have long
necks.
Darwin
• Due to variation in the
population there is a
range of neck lengths.
Some animals naturally
have longer necks than
others.
• Those with longer necks
can reach the tree
leaves.
Comparison of Lamarck’s and
Darwin’s Ideas on Evolution
Lamarck
In the event of a shortage
of grasses (drought), the
animals are able to feed
on leaves.  The long
necked animals are the
most fit! These are the
animals that survive and
reproduce.
Darwin
In the event of a shortage
of grasses (drought), the
animals are able to feed
on leaves.  The long
necked animals are the
most fit! These are the
animals that survive and
reproduce.
Comparison of Lamarck’s and
Darwin’s Ideas on Evolution
Lamarck
Darwin
• Over the next
generations, the longer
necked animals will
continue to stretch and
elongate their necks.
• Each generation will pass
on their longneck to their
young
• Over the next generations,
(due to mutations, new
gene combinations, crossing
over) there will again be
variation in neck length
• Those with the longest
necks will be be most fit-with the greatest chance of
survival.
Microevolution
according to
Darwin’s Ideas
on Natural
Selection
Macroevolution according to
Darwin’s Ideas on Natural
Selection
Speciation = formation of new species
Variation and Natural Selection
• Most
phenotypes
(traits) are
polygenic.
• A graph of
these traits
often shows a
bell curve.
Types of Natural Selection
Disruptive
Stabilizing
Directional
Stabilizing Selection
• If individuals near the
center of the bell
curve have higher
fitness (= leave a
greater amount of
fertile offspring) then
stabilizing selection
occurs.
Directional Selection
• If individuals at
one end of the
bell curve have
higher fitness
then directional
selection
occurs.
• Example: long
necks
Disruptive Selection
• If individuals at
both ends of the
curve have
higher fitness
than those in
the middle then
disruptive
selection
occurs.
Genetic Drift
• If a small population is isolated from
others of the same species, it is possible
that just be “chance” one allele may
become more common in a population.
Genetic Drift
• For example: The Bronx, NY, becomes
built up and trees are cut down. Few
squirrels are able to survive. However,
one section of the Bronx is set aside for
the development of the Bronx Zoo. Trees
I’ I’mNOT
an
are
cut down in this area. By chance,
Eastern
Gray
several
of the gray squirrels in the area of
Squirrel
the zoo have black fur (a variation in fur
color). Over time, the allele for black fur
becomes common in this population.
How do new species form?
Example: Galapagos Finches
• A small group of a species of finch arrives
on one of the Galapagos Islands
• These finches do not usually fly across
open water—they may have gotten lost or
were blown there by the wind.
Speciation continued!
• Over time these original finches may have
ended up on other of the Galapagos
Islands through some chance occurrence.
• USUALLY the finches do NOT fly from one
island to another.
Speciation continued!
• The Galapagos Islands had different
environments.
– Some had a low elevation and were dry with
little plant material.
Speciation continued!
• Others had a higher elevation with greater
rainfall and many plants.
Speciation continued!
• Directional selection occurs:
– One island may have seeds that are large and
difficult to open.
– Birds with a larger, thicker beak will have the
highest survival rate on this island
Speciation continued!
• Directional selection occurs:
– Another island may have seeds that are small
and easy to open
– Birds with a small, thinner beak will have the
highest survival rate on this island
Speciation continued!
• Reproductive Isolation: if the populations
remain separate, and their gene pools
continue to change, eventually they can no
longer mate with each other—they are
then TWO NEW SPECIES!!!
• On the Galapagos Islands this processes
resulted in the evolution of 13 different
finch species.
Darwin’s
Finches
Cladograms – a diagram of
evolutionary relationships
Cladograms – a diagram of
evolutionary relationships
• At the beginning of a cladogram is a single
branch. This branch then splits several times
into the several animals you have on a
cladogram.
• When you follow along a branch of the
cladogram, it sometimes splits at nodes into two
or more branches.
• You can also tell how closely related animals are
on the cladogram. If you want to know the
closest relative of one animal you trace its
branch back to the most recent node.
Which are more closely related: roundworms and
annelids (earthworms) or arthropods and
annelids?
Cladograms
• Each node represents a new trait that has
evolved and the common ancestor that
evolved that trait.
• As you follow an animal’s path in the
cladogram from the beginning to the end,
you can find out the animal’s adaptations
through time. Each node it goes through is
a trait that it evolved, in that order.
Cladograms
• 100 million years
go by …
Cladograms: Complete the
table below!
• Use the information in the table to
construct a cladogram of these animals.
Organism
Derived characteristics
Backbone
Legs
Hair
Earthworm
Absent
Absent
Absent
Trout
Present
Absent
Absent
Lizard
Present
Present
Present
Present
Absent
Present
Human
Making a Cladogram
• Which organism is least like the others?
Earthworm
Organism
Derived characteristics
Earthworm
Backbone
Absent
Legs
Absent
Hair
Absent
Trout
Present
Absent
Absent
Lizard
Present
Present
Present
Present
Absent
Present
Human
Making a Cladogram
• Use your worksheet on cladograms as your
guide.
• Develop a cladogram showing the evolutionary
relationships between all 4 animals.
Organism
Derived characteristics
Backbone
Legs
Hair
Earthworm
Absent
Absent
Absent
Trout
Present
Absent
Absent
Lizard
Present
Present
Present
Present
Absent
Present
Human
Making a Cladogram
Earthworm
Trout
Lizard
Human
Hair
Legs
Backbone
Which animal is species X most closely
related to on the cladogram?
Earthworm
Trout
Lizard
X
Hair
Legs
Backbone
Human