EVIDENCE FOR

EVOLUTION2015 - TOPIC 5

EVOLUTIONThings to coverBiogeographyThe fossil recordComparing moleculesComparing 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

BIOGEOGRAPHYEVIDENCE #1

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.

FOSSIL RECORDS

EVIDENCE #2

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 decaysat 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 areathat 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.

amber

mud

ash/mud

ice and frozen soil

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

COMPARING MOLECULES

EVIDENCE #3

COMPARING MOLECULES Scientists can compare a

variety of molecules in order to determine whether two species are closely or distantlyrelated.

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. +

◦ high degree of pairing

◦ eg. +

◦ 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.

COMPARING ANATOMY

EVIDENCE #4

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

• 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.

record common ancestry homologous functions functional chemical

bonding

environments common history analogous structural base

sequencedouble

helix

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.