The Evidence
for Evolution
Evidence for Evolution
• Every idea that is put forth in science needs
evidence to back it up before it is accepted by
those who work in the field.
• Evolution has many pieces of evidence that
support it. These include:
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The Fossil Record
Homologous Structures
Embryology
Geographic Distribution
Molecular Biology
Chromosomal Action
Protective Resemblance
Artificial Selection
The Fossil Record
• The study of fossils and the fossil record is
called paleontology.
• Fossils provide some of the strongest pieces
of evidence for the theory of evolution. The
fossil record includes many items such as
fossilized bones, preserved specimens (in
amber), imprints, petrified remains and
microfossils.
• It is generally accepted that the deeper the
layer of rock, the older the materials of the
rock and of those things found in the rock.
Fossils that are deeper are older while those
that are closer to the surface are newer/more
recent.
• Throughout the fossil record, one can plainly
see a flow of form as you go back in geologic
time.
The Fossil Record
Homologous Structures
• Homologous structures are parts of the
body (found on sometimes, very
different species) that have a similar
structure even though they may have
entirely different functions.
• Again, traits come from DNA…DNA from
parents…So similar traits…similar
DNA…similar ancestral parents.
• The forelimb of many mammals is a
great example of homologous
structures.
Homologous Structures
Vestigial & Analogous Structures
• Vestigial structures are structures that are
not used by and organism but hint at its
evolutionary past.
• Vestigial structures are used as evidence for
evolution along the same lines as homologous
structures.
– The human appendix or the hind digits on dogs are
an example of vestigial structures.
• Analogous structures are structures that
have a common function but not in origin or
anatomical structure.
• Analogous structures are not an example of
evolution.
– A birds wing and a butterflies wing may both aid in
flight and look pretty but they are constructed quite
differently.
Vestigial & Analogous
Vestigial Structures
• Femur in Whale
• Human Structures
Analogous
Structures
• Insect wing vs. Bird
or Bat Wings
• Shark vs. Dolphin
Embryology
• Embryology is the study of the embryonic
development of seemingly unrelated species.
• You will see many similar structures between
“unrelated” species if you compare the earlier
stages of embryonic structure. These structures
include the gill slits (even on terrestrial species)
and the elongated tail (even on those without tails
at birth).
• As the embryos develop, you see the divergences
that have occurred between the species as they
all adapt to their future environments. It’s like
evolution on fast-forward.
Embryology
Molecular Biology
• The molecules that make up living things
are called biomolecules. (Carbs, Lipids,
Proteins and Nucleic Acids)
• All living things use these molecules in their
structure and function in much the same
way.
• A great example of this is the cell
membrane (phospholipid bilayer) and
protein structure (amino acids).
Chromosomal Action
• The chemical composition of chromosomes in all
living things is similar (as you just saw).
• To go along with this, the actions chromosomes
perform during cell division are repetitive in many
different, seemingly unrelated, species.
• Think of mitosis…Coil, pair, middle, separate!
Geographic Distribution
Using the Past…
• Fossils of related species have been found on
land masses that were once very close to each
other but now reside thousands of miles away
from each other.
• South America and Africa were once beside each
other as part of the super continent of Pangaea
but now they are far apart, yet, fossils that are
remarkably similar have been found on once
neighbouring coastline of each continent.
Pangaea
Geographic Distribution
Using the Present…
• If you look at species that live in a specific
environment, like a mountain example, those
species will have more in common with species
that live in other mountains – even if the
mountains are thousands of miles apart.
• Many times, a species will have more in common
with something that resides in a similar
environment that is very far away, than it does
with something that lives in a neighbouring
environment.
• This shows the impact of environmental selection
pressure on the structures a species will possess.
Same But Different!
Protective Resemblance
• The peppered moth resides in England in large
stands of birch trees and other lightly-coloured
flora.
• The moth has a light and dark form (in terms of
the colouration of its wings and body).
• The light ones dominated the forest as they were
able to hide better from predators – the dark ones
showed up more easily and their numbers were
kept smaller.
• The industrial revolution began in the 1800’s and
the factories began to spew smoke and soot onto
the nearby forests. What do you think happened
between the two peppered moth variants?
Protective Resemblance
Artificial Selection
• AKA: Domestication
• Artificial selection
occurs when humans
chose the desired traits
within a species and
select which individuals
shall be bred and give
rise to the next
generation.
• The humans select the fit
individuals instead of the
environment – hence the
name artificial selection.
• The dogs below are the
result of people choosing
their traits – not nature.
That’s All I Got…Oh…And This…