EVIDENCE FOR
EVOLUTION
2015 - TOPIC 5
EVOLUTION
Things to cover
Biogeography
 The fossil record
 Comparing molecules
 Comparing anatomy

WHAT DO YOU KNOW?
WHAT DO YOU KNOW?
WHAT DO YOU KNOW?
WHAT DO YOU KNOW?
WHAT DO YOU KNOW?
EVIDENCE FOR EVOLUTION

The evidence that supports Darwin’s theory includes:
◦ Biogeography
◦ Fossil record
◦ Comparing molecules
◦ Comparing anatomy
EVIDENCE #1
BIOGEOGRAPHY
BIOGEOGRAPHY

Refers to geographical distribution of species

Evolution would suggest that similarities would exist
between species and those living in that area in the
past.

If organisms arose by ‘special creation’,
we would expect that similar habitats
in different parts of the world would
contain similar plant and animals.

But they don’t….
BIOGEOGRAPHY

We find that unique organisms live in similar habitats in
different parts of the world.

In Australia, our deserts contain spinnifex grass and salt
bush. American deserts contain cacti.
EVIDENCE #2
FOSSIL RECORDS
FOSSIL RECORDS

Refers to the record kept of the evidence of life in the
past

Fossils don’t have to be bones!

They can also be:
◦ Teeth
◦ Feathers
◦ Scales
◦ Branches
◦ Leaves
◦ Footprints, etc
FOSSIL RECORDS

Steps:
1. Organism dies
2. Covered by dirt, mud, silt or lava before
decomposition can occur
3. The material that lies
above the fossil
compress, forming rock
4. This preserves the fossil.
Even if the organism itself decays
at a later stage, the imprint will remain in the rock.
FOSSIL RECORDS
FOSSIL RECORDS

Fossilisation is rare!
– It has to be buried before it decomposes.
– It has to be buried in an area
that favours fossilisation.
ie. no silt, no fossil
– Whole organism may not be
fossilised due to an attack by
predators before being buried.
FOSSIL RECORDS

Fossilization is a rare event.
◦ Different types of fossil form under different
conditions and environments.
◦ Fossilized remains only form in the absence of
microbes, which need food, oxygen, water and
warmth.
ice and frozen soil
ash/mud
mud
amber
FOSSIL RECORDS
FOSSIL RECORDS

Finding a fossil is also rare!
1.
You need to know where to look! And even then, its
hard!
2.
May only find pieces; not enough to get the whole
picture of that organism.
3.
May only find one organism.
Good scientists never rely on one piece of evidence to
draw a good conclusion.
4.
May only find one gender.
Many species are sexually dimorphic – meaning that
males and females differ.
FOSSIL RECORDS

If a new species evolves from an ancestral species,
the fossil record should contain organisms that are
intermediates with some features of both the modern
and ancestral forms.

Birds are believed to have
evolved from reptiles.

One fossil type found is
Archeopteryx lithographica.
FOSSIL RECORDS

Archeopteryx lithographica
REPTILE
FEATURES
BIRD FEATURES
teeth
feathers
a long, bony tail
wings
claws on wings
a wishbone
FOSSIL RECORDS
EVIDENCE #3
COMPARING
MOLECULES
COMPARING MOLECULES

Scientists can compare a
variety of molecules in order
to determine whether two
species are closely or distantly
related.

eg:
◦ DNA
◦ Amino acid sequences
& proteins
COMPARING MOLECULES

DNA HYBRIDISATION
◦ All organisms contain DNA in their cells.
◦ Double stranded DNA can be heated so that it
separates into single strands.
◦ A single strand from one organism can be placed next
to a single strand from another organism and cooled
down.
COMPARING MOLECULES

DNA HYBRIDISATION
◦ The two single strands will bond to each other
(hybridise) where complementary bases are found.
◦ If the strands are similar, a high amount of pairing
will take place.
◦ eg.
+
◦
◦ eg.
◦
 high degree of pairing
+
 low degree of pairing
COMPARING MOLECULES

COMPARING PROTEINS
◦ All organisms share a number of proteins.
◦ Cytochrome C is an enzyme needed for respiration.
◦ If we compare the amino acid structure of
Cytochrome C in different organisms, we find that
closely related organisms have very similar
Cytochrome C.
COMPARING MOLECULES

COMPARING PROTEINS
Organism
No. of changes in amino
acid sub units relative to
humans
Human
0
Rhesus monkey
1
Whale
7
Chicken
13
Tuna fish
22
COMPARING MOLECULES

COMPARING PROTEINS
◦ The longer that two species diverged from a common
ancestor, the more time there has been for changes
to occur in the amino acid sequence.
◦ This shows that humans and monkeys are more
closely related than humans and fish.
EVIDENCE #4
COMPARING
ANATOMY
COMPARING ANATOMY

Scientists look for similarities in bone structure and
embryos in order to investigate common ancestry.

These similarities are called homologies.

Species that share homologous structures share
similarities because they have a common ancestor.

eg:
◦ The forelimb of all mammals is very similar in the
number and structure of the bones present.
COMPARING ANATOMY
COMPARING ANATOMY

Analogous structures also exist.

These are similarities in structure that have evolved due
to similar environmental selection pressures.

eg:
◦ The fin of a shark (cartilaginous fish) and a dolphin
(mammal).
REVIEW – TOPIC 5
record
common
ancestry
homologous
functions
functional
chemical
bonding
environments
common
history
analogous
structural
base
sequence
double
helix
The fossil ________ provides evidence that supports Darwin’s
theory.
• Fossils can show ________ structures. These are structures that
have a similar structure due to ________ ________ , but have
evolved to suit different ________ .
• ________ structures do not result from common ancestry.
These structures share ________ similarities due to their use
for shared functions, in shared ________ .
• Similarities in DNA ________ ________ can also provide
evidence that supports Darwin’s theory.
•
REVIEW – TOPIC 5
•
•
•
•
The fossil record provides evidence that supports Darwin’s
theory.
Fossils can show homologous structures. These are
structures that have a similar structure due to common
ancestry, but have evolved to suit different functions.
Analogous structures do not result from common
ancestry. These structures share structural similarities due
to their use for shared functions, in shared environments.
Similarities in DNA base sequence can also provide
evidence that supports Darwin’s theory.