Scientific Evidence for
Evolution
Fossils
Fossils are a strong piece of evidence
to support the theory of evolution.
Fossil = preserved remains or marking
left by organisms that lived in the
past. (Latin fossilis means “dug up”)
Types of Fossils
Sometimes full
organisms can be
preserved in sticky
amber that hardens.
Amber is a resin that
is produced by trees
– you should be
familiar with this
from Jurassic Park!
Types of Fossils
Organisms can be
preserved for
millions of years in
very cold
environments. An
example of this is
the woolly
mammoth found
recently in Russia.
Types of Fossils
In addition, animals can be trapped in tar and
preserved like in the La Brea tar pits in LA.
Types of Fossils
By far the greatest numbers of fossils form on the
bottoms of lakes and seas. Sometimes the shape
of an organism is preserved in rock as a mold.
Sometimes a mold fills with minerals and forms a
cast which is a copy of the original organism.
When impressions
are made in mud,
such as animal
footprints, they are
called imprints.
Age of Fossils
Most fossils are found in sedimentary rock… so
called because sediments from eroded rock on land
collect in rivers, seas and oceans and harden.
Age of Fossils
Over millions of years, the shifting of the
earth’s crust has raised some regions that
one were under the seas and the layers are
visible. The Grand Canyon is an example.
Age of Fossils
What can you conclude about the age of these
organisms in the layers of sedimentary rock?
Why Fossils are
Strong Evidence
• The sequence of fossils is consistent all
over the Earth = consistent evidence of
change through time
• Many transitional forms of fossils have
been found (fish to amphibian, amphibian
to reptile)
Transitional
forms in whale
evolution
Did you ever wonder why we
have wisdom teeth?
Vestigial Structures
Scientists hypothesize that at one point,
our ancestors needed these extra teeth!
They are an example of a vestigial
structure. Vestigial is a scientific word for
“left-over.” These structures are usually
reduced in size and serve little or no
function. Scientists use the presence of
vestigial structures as evidence that
evolution has occurred.
Other examples…
Vestigial Structures
In the human body there are
more than 100 vestigial
structures!
Take the tailbone, for instance.
It is the evolutionary remnant of
a ancestral, reptilian tail! No
muscles attach to it, it has
nothing to do with balance or
anything else. So then why do
we have it?
Vestigial Structures
This is a picture
of an appendix
that is being
removed
because it is
infected.
Vestigial Structures
Horses use their
appendix to break
down cellulose plant
cell walls. Ours has
no function! Does
that mean ours lost
its function as we
evolved?
Vestigial Structures
And why do we have muscles to move our
ears when they don’t work?
(Except for that friend of yours that can
wiggle their ears when they concentrate )
Vestigial Structures
What do you notice about this whale skeleton?
Vestigial Structures
It has “left-over” hind leg bones!!!
The tail side of the snake below
also has remnants of a pelvis….
What could this mean??
Scientists conclude that
both whales and snakes
evolved from four-legged
ancestors…
Why else would they have
these structures?
Vestigial Structures
1.Fingernails on manatee fins which evolved
from legs
2.Cave-dwelling organisms such as crayfish
that have eyestalks but no eyes
3.Species of flightless beetles and birds that
have wings.
Okay, now that I have your
attention…
Do you remember what the study of
structure is called?
Anatomical Similarities
If you said ANATOMY, you are right!
There are certain structural similarities
among living things that scientists point to as
more evidence for evolution.
Let’s take a look…
Anatomical Similarities
The structure of the arm and hand of a human,
the flipper of a whale, the limb of a cat, the
wing of a bat and the wing of a bird are quite
different in appearance because they are
adapted to perform different functions.
Even with these different functions though,
inside the structures are surprisingly similar…
Anatomical Similarities
Parts of different organisms that have
similar internal structures, but different
forms and functions are called
HOMOLOGOUS STRUCTURES.
Homologous structures are regarded as
evidence that some species evolved from a
common ancestor.
Anatomical Similarities
Be careful though! Sometimes animals
have similar parts that are different in
structure and development. Look below…
Anatomical Similarities
Although insects and birds both have wings,
they are different in structure. An insect wing
does not have bones at all – it is made of a
tough substance called chitin.
Structures that have similar external forms and
functions but different internal structures are
called ANALOGOUS STRUCTURES. These
structures are NOT used as evidence for
evolution.
Two of these embryos are human,
one is the embryo of a pig. Can
you pick out the pig embryo?
Comparing Embryos
• It’s weird that you can’t really tell! But the
one on the right is the pig embryo
• Comparing the embryo development of
different species can provide additional
evidence of evolutionary relationships
because embryos of closely related
species show similar patterns of
development.
For example…
Comparing Embryos
• All vertebrate embryos have gill slits,
two-chambered hearts and tails at some
point in their development.
• These similarities support the idea that
they have a common origin.
And now on to the last
piece of major evidence for
evolution….
Biochemical Comparisons
All forms of life have DNA. There are leftover
sections of DNA that are called junk DNA
because they don’t have a purpose. Maybe they
did at one time?
Biochemical Comparisons
A wide range of organisms from fruit flies to
worms to mice to humans have very similar
sequences of genes that are active early in
development.
Remember from the movie scientists put
mouse eye genes in an eyeless fruit fly & eyes
developed!
What can this mean?
These genes were present in a very early
common ancestor of all these groups.
Biochemical Comparisons
On top of that…
Proteins in all organisms are composed of the
same set of 20 amino acids.
And hemoglobin is found in almost every
multicellular animal.
The more closely related two organisms are,
the more similar their DNA code is.
Biochemical Comparisons
For example, chimp DNA and human
DNA are 98.2% similar!
Well, what do you think?
You must agree that the
observations themselves cannot be
refuted.
However, do you agree with the
interpretation of these observations
and their use to support evolution?
The particulars of the jump from nonliving to
living that occurred sometime in our planet's
early history is a profound enigma and will likely
remain that way for some time to come, says
Harvard's Andy Knoll.
The hard part, and the part that I think nobody
has quite figured out yet, is how you get them
working together. How do you go from some
warm, little pond on a primordial Earth that has
amino acids, sugars, fatty acids just sort of
floating around in the environment to something
in which nucleic acids are actually directing
proteins to make the membranes of the cell?
In the early 1950s, Stanley Miller essentially put
methane (natural gas), ammonia, hydrogen gas,
and water vapor into a beaker. This was a view
of what the primordial atmosphere would have
looked like.
He put an electric charge through that mixture to
simulate lightning going through an early
atmosphere.
After sitting around for a couple of days, all of a
sudden there was this brown goo all over the
reaction vessel.
When he analyzed what was in the vessel, rather
than only having methane and ammonia, he
actually had amino acids, which are the building
blocks of proteins.
In fact, he had them in just about the same
proportions you would find if you looked at
organic matter in a meteorite. So the chemistry
that Miller was discovering in this wonderful
experiment was not some improbable chemistry,
but a chemistry that is widely distributed
throughout our solar system.