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Classify the following:
Trout, catfish, frog,
snake, whale, human,
cardinal, turtle,
salamander, shark,
dolphin, bat, blue jay,
http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
Did you group them by movement?
SWIMMERS
Trout
Catfish
Whale
Shark
dolphin
FLIERS
cardinal
bat
blue jay
HOP/CRAWL/SLITHER
frog
turtle
snake salamander

UPRIGHT
Human
Or by:
FISH
trout
catfish
shark
BIRDS
blue jay
cardinal
AMPHIBIANS
frog
salamander
REPTILES
snake
turtle
MAMMALS
whale
dolphin
human
bat
Evidence for evolution
Scientists compare these things to
determine the evolutionary
relationships among organisms.
1. body structures
2. development before birth
3. DNA sequences
1. SIMILARITIES IN BODY STRUCTURE
An organism’s body structure is its basic
body plan (ex. How its bones are arranged.)
The 5 classes of vertebrates (fish,
amphibians, reptiles, birds and mammals) all
have a similar body structure: Internal
skeleton w/a backbone.
HOMOLOGOUS STRUCTURES:
similarities in structure inherited from
an early common ancestor
2. Similarities in Early Development
 Scientists can also make inferences
about evolutionary relationships by
comparing the early (embryonic)
development of different organisms.
rat
chicken
turtle
3. Similarities in DNA
 Scientists infer that the species inherited
many of the same genes from a common
ancestor.
 Genes are made of DNA. By comparing the
sequence of nitrogen bases in the DNA of
different species, scientists can infer how
closely related the species are. The more
similar the sequences, the more closely
related the species are.
Because of its appearance, the tiny
elephant shrew was once thought to be
closely related to mice. DNA analysis
shows that they are much more closely
related to elephants! Ya never know!!
Combining evidence
Scientists have combined evidence
from fossils, body structures, and
early development, and DNA and
protein sequences to determine
the evolutionary relationships
among species.
 An example of how scientists combined
evidence from different sources is shown
in the branching tree. A branching tree is
a diagram that shows how scientists
think different groups of organisms are
related.
Below image from Prentice Hall Life Science.
Most recent species at
top of tree
Time moves
from the past
at the bottom
to present
time at the
top to
Forks=Where
species began
to evolve away
from their
common
ancestor
Common
ancestor
at bottom
of tree
Natural Selection
 The process by which
individuals that are better
adapted to their environment
are more likely to survive and
reproduce than other members
of the same species.
4 Parts of natural
selection:
 1-overproduction
 2-competition/struggle to survive
 3-variations
 4-selection/successful
reproduction
1. Overproduction
 Most species produce far more off
spring than can possibly survive
 Often so many are produced that
there are not enough resources for
them all.
 Ex: Sea turtles
What would happen if all the
young sea turtles lived?
Sea turtles lay 100s of eggs—if
they all survived, the ocean
would be full of turtles.
Darwin knew better…
2. Competition
 Offspring must compete with
each other to survive.
 Competition does not
necessarily mean physical
fighting.
 It is usually indirect
For example,
Some baby turtles
May not be able to find enough to
eat.
Variations
 Members of a species differ
from each other in many of
their traits.
 Any difference in between
individuals of the same
species is called variation.
For example…
Some turtles
are able to swim
faster than others
To escape from
predators.
 Remember you don’t have to
be faster than the predator,
you just have to be faster
than the other prey!
Selection
 Over a long period of time,
natural selection can lead to
evolution.
 Helpful variations gradually
accumulate in a species, while
unfavorable ones disappear.
For example…
 A new faster predator moves
into the turtles’ habitat.
Perhaps a faster
breed of shark…
The turtles that are able to
swim faster would be more
likely to escape from the
new predator.
 The faster turtles would be
more likely to survive and
reproduce. Over time, more
turtles in the species would
have the “fast-swimmer” trait.
Genes
 What role do genes have in
evolution?
 Variations can occur due to
mutations in genes or from the
shuffling of alleles during meiosis.
 Therefore, only traits that are
inherited are acted upon by
natural selection
How are new species formed?
 A new species might form when a
group of individuals remains
separated form the rest of its
species long enough to evolve
different traits.
 This is called isolation or
complete separation.
Continental drift
 Millions of years ago on the super
continent Pangaea, organisms
could travel from one part of the
continent to another.
 Pangaea gradually split apart
over millions of years in a
process called continental drift.
 As this separation happened,
species became isolated from
one another and began to
evolve independently.