Before we begin….
• Spend the next ten minutes writing down how
you think evolution works – i.e. how would
you explain it to a non-biologist?
• Write your name on it and hand it in.
The evolution of evolution
• Biological evolution describes the change over time in the
genetic composition of a population of organisms
• The evidence from the fossil record and
genetics is overwhelming but the theory
is itself ever-evolving
Erasmus Darwin (1794)
• All living organisms originate from common
ancestor – gave no mechanism
Lamarck (1809)
• Proposed a mechanism
for how changes in a
species could come about
– Changes acquired in a
lifetime could be passed on
to their offspring, causing a
gradual change in the
species
Read his views on snakes – pg
507
Darwin and Wallace (1859)
Theory of evolution by natural
selection (or survival of the
fittest)
• Organisms produce more offspring
than can survive
• Offspring show variation. Some
variations more suited to
environment than others
• Those individuals with favourable
characteristics more likely to survive
and produce more offspring
• Successive generations will become
http://www.youtube.com/watch?v=2d_Qqknr modified over time – eventually
becoming a new species
6SU
Mendel (1865)
• Model of inheritance
largely ignored for 30
years
• In 1900 rediscovered
and accepted
August Weismann (post 1896)
• Neo-Darwinism
combines Darwin’s
theory of natural
selection with
population genetics and
theory of inheritance
Geological Time
•
This time scale was developed in the
nineteenth century when geologists
observed that particular rocks were
characterised by distinctive groups of
fossils.
•
Names where based on areas where
they were first recognised or on the
distinctive nature of the rocks.
•
Geological time scale divided into Eras
(e.g. Precambrian), Periods (e.g.
Proterozoic) and Epochs.
•
The most widely used time intervals
are Periods.
•
The time interval predating the
appearance of the first abundant
fossils is called the Precambrian.
Three Rock Types
• Igneous Rocks- formed from molten
rock.
• Sedimentary Rocks – formed from the
compaction of various sediments
(sand, mud and clay) under heat and
pressure. Sediments vary in size and
are deposited under water or by wind.
• Metamorphic Rocks- these are
sedimentary or igneous rocks that
have been changed due to the action
of extreme heat and pressure.
A Dynamic Planet
• Earth is constantly changing
in:
• the position of the continents
• global temperature and
climate
• sea levels
• the number of species that
make up the biosphere.
• These changes are both:
• natural (e.g. earthquakes,
tsunami and volcanic activity)
and
• human induced (e.g. climate
change).
Plate Tectonics
• The Earth’s crust is
fragmented into a number of
plates that move on the fluid
mantel that overlies the
Earth’s core.
• Land masses – the continents
are carried on those plates.
• Over time these plates move,
driven by convection
currents generated by the
heat in the Earth’s core.
• The movement is about as
fast as your fingernails grow!
http://www.youtube.com/watch?v=QDqskltCixA
Plates side by side
• The San Adreas Fault in
California USA, is an example
of a transform plate
boundary.
• Here the American Plate and
the Pacific Plate are sliding
past one another.
• At times the plates get stuck.
This causes pressure to build
up.
• When the pressure is finally
released earthquakes result.
When Plates Collide
• When two plates converge, one plate is forced under the other plate in
what is called a subduction zone.
• The Nazca Plate is being forced under the South American Plate. The Andes
is the result of this action. Many peaks in the Andes are volcanically active.
When Plates
Move Apart
• New crust forms from
molten material that rises
up when plates move apart.
• Divergent plate boundaries
are responsible for rift
valleys and new ocean floors
and mid ocean islands.
• The great rift valley of East
Africa is a young divergent
plate boundary.
• The African plate will
continue to move
northwards, slowly
closing the
Mediterranean sea and
driving up mountain
ranges in Southern
Europe.
• Australia will continue
to move north (about
5cm/year) colliding with
SE Asia.
• America will continue to
move away from Europe
and Africa as the
Atlantic Ocean widens.
Biogeography
• Biogeography is the study of the geographical distribution of plants and animal
species based upon their evolution and dispersal.
• The world is divided into biogeographical regions that roughly correspond to the
continents.
• Provides evidence for plate techtonics and continental drift.
Take a walk through Geological Time
The Present
200 Mya
542 Mya
The Dating Game
• How do we determine the ages of rocks and
fossils?
– Relative time
– Stratigraphic correlation
– Absolute time
Relative Time
The Principal of Rock Succession
“in an undisturbed sequence of
layered rocks, the oldest layers lie at
the bottom and the successively high
layers are progressively younger”.
This principal can be applied to any
fossils that are contained in the
layers.
A rock succession
Stratigraphic Correlation – Using Index Fossils
• Index fossils are geologically short lived species with a limited occurrence
so that they are restricted to a particular sedimentary strata.
• The presence of such fossils in a particular strata, even in widely separated
regions, are used to infer the strata as being of the same age.
Location 1
Location 2
Absolute Time
• Reliable technique that assigns a numerical date to the
sample.
• Techniques include radiometric dating, electron spin
resonance and luminescence
• Radiometric dating is the most common technique.
Radiometric dating
• The method is based upon the
radioactive decay of unstable
atoms to a more stable atom.
• In a certain period of time, called
the half life, half of the unstable
atoms will have decayed into the
more stable atom.
• By measuring the ratio of
unstable to stable decay
products, the time that has
elapsed since the decay began
can be calculated. This is
equivalent to the age of the rock.
Radiometric dating
• Carbon 14 – (HL: 5,730 years) used to date objects
younger than 70,000 years.
http://www.youtube.com/watch?v=udkQwW6aLik&feature=related
Radiometric dating
Carbon dating is not useful for organic material older than about 60 000 years ago.
However, another technique of dating, known as electron-spin resonance (ESR), is
useful for ages from about 50 000 years ago to 500 000 years old.
Evidence for Evolution WebQuest
• http://www.pbs.org/wgbh/evolution/educato
rs/lessons/lesson3/act2.html
The Fossil Record
• Fossils are the remains or traces of
pre-existing life forms preserved in
rocks.
• Usually only the hard parts (shells
or skeletons) are preserved.
• Trace fossils are the signs or
remains of an organism’s activities
such as footprints, bite marks,
burrows and coprolites.
• Fossil remains have been found
across 3,500 million years of Earth’s
history, but there are gaps in the
fossil record.
• The fossil record is evidence of
biological evolution.
Fossilisation
• Fossils are formed when an
organism dies and the body
or part of the body is
preserved in some way.
• Usually, the body needs to
be rapidly buried in
sediments.
• Rapid burial prevents
destruction of the organism
by predators, bacterial or
weathering.
Fossilisation
• Burial can occur:
– on the bottom of the
sea, rivers, and lakes
– on land by blowing sand
or volcanic ash,
– by the entrapment of
the organism in some
sticky substance such as
tar or tree sap (amber).
Fossilisation
• After burial, fossils may
undergo a variety of
physical and/or chemical
changes depending upon
the environment of the
enclosing sediment.
• As successive layers of
sediment build up, the fossil
may be flattened and
distorted as the sediment is
hardened into rock by heat
and pressure.
Fossilisation
• Chemical changes occur as
the original hard parts are
progressively replaced by
other minerals such as
quartz or opal in a process
called petrification.
• Or the hard parts may be
dissolved away completely,
so that an impression or a
natural mould of them
remains in the rock.
Types of Fossils
• When an organism
decays it leaves a cavity
known as a mould.
• When the cavity is later
filled by other material
a cast is formed.
Impression of the hard exoskeleton of a trilobite
that lived during the Cambrian Period, about 500
mya.
Types of Fossils
• Thin tissue is sometimes
preserved as a carbon film
or impression in a rock.
Types of Fossils
• Ammonoid fossil shell
from the Jurassic Period
(England). The shell has
been replaced with iron
sulphide (pyrite).
• Cockle shell replaced
with opal from
Cretaceous Period,
Cooper Pedy, SA.
Types of Fossils
• Petrified tree
trunk in Arizona.
• Plant material is
replaced with
mineral salts that
petrified the
tissue – the tree
literally turns to
stone.
Types of Fossils
• A human cast formed in
volcanic ash at Pompeii.
Types of Fossils
Fossils are not only found in
rock!
• Animals have been trapped in
natural tar pits.
• Mammoths and other animals
have been trapped in ice or frozen
underground, so that flesh and
stomach contents have been
preserved.
• Extinct insects have been found in
amber (tree sap).
Insect preserved in amber from the Baltic
Region dated from the Oligocene Period
What the fossil record shows….
http://faculty.icc.edu/easc111lab/labs/labf/geologicalscaleclock/geologicscale_clock.html
Increasing Structural Complexity of Life Forms
Making Connections: Transitional Fossils
• Fossils that are
intermediate between
the ancestral form and a
new species.
• If birds have evolved
from reptiles the fossil
record could show a
fossil that has
characteristics of both
reptiles and birds.
e.g. Archaeopteryx
First Life Forms
• Prokaryotic life forms existed
~3.5 billion years ago.
• Stromatolites are structures
formed by primitive e
photosynthetic cyanobacteria
communities.
• The structures are made up of
many fine concentric layers of a
hard limestone-like substance
deposited by the bacteria.
• The stromatolites are the most
notable fossil of the
Precambrian.
Right: Shark Bay, Western Australia
The Story of Oxygen
• The atmosphere of the early
Earth contained little oxygen.
• Oxygen slowly accumulated in
the atmosphere during the
Precambrian due to the action
of photosynthetic prokaryotes.
• The build up of oxygen saw the
development of new
biochemical pathways and the
development of eukaryotic
cells ~ 1.7 billion years ago.
Mass Extinctions
• Mass extinctions are on a global scale when biological
diversity markedly decreases by a large number of species
becoming extinct in a short time.
The Link
• http://www.youtube.com/watch?v=9dIGf1tgRVc
(10 mins – please watch in own time)
Homology
• Homologous structures: different organisms,
have an underlying similar basic pattern.
• Molecular homology: refers to similar
sequences of nucleotides in DNA and/or
amino acids in proteins.
Homologous structures
• Comparative anatomy: Related organisms will show
similarities in basic structures regardless of their way of
life.
Homologous structures
• Comparative anatomy (embryology): in embryonic
development (
– e.g. all members of phylum Chordata (including humans)
have a dorsal notochord, pharyngeal slits and a dorsal nerve
cord
Homologous structures
Each leaf has a very different shape and function, yet all are
homologous structures, derived from a common ancestral form.
Molecular Homology
• Molecular changes accumulate over time in DNA.
These genetic changes are reflected in the
sequences of amino acids.
• Closely related organisms will show similarities in
their molecular makeup.
• The longer the separation between two species
(since they shared a common ancestor) the
greater the accumulation of molecular
differences over time.
Molecular Homology
• All proteins are composed of the same set of
twenty amino acids. We can compare the
similarities in amino acid sequences.
• DNA sequences from difference species can be
compared in terms of their order of nucleotides.
• Genomes can be compared for what genes they
have in common.
Molecular Homology
• Cytochrome C is a vital protein in the electron
transport chain in aerobic cellular respiration.
• Difference in cytochrome C between species:
– Human and Rhesus monkey: 1 amino acid
– Human and whale:
7 amino acids
– Human and bird:
13 amino acids
– Human and tuna fish:
22 amino acids
Gene Sequences
• Species that are closely related will show more similarities
in the base sequences of their common genes.
• Gene sequences may be strongly conserved over time.
• Strongly conserved genes will show very similar base
sequences. E.g. Haemoglobin
– Human:
– Orangutan:
– Rabbit:
TGA CAA GAA CA
TCA CGA GAA CA
TGG TGA TAA CA
DNA Hybridisation:
Measuring relatedness
Single DNA strand from species 1
Single DNA strand from species 2
• Heat double stranded fragments and record
temperature at which half become single
stranded again. This is known as the melting
temperature.
– Lower melting temperature = the lower the
complementary pairing
– Higher melting temperature = the higher the
complementary pairing
Mitochondrial DNA (mtDNA)
• All eukaryotic cells contain
mitochondria.
• Mitochondria were once free
living prokaryotes that became
incorporated into the eukaryotic
host cell.
• They carry their own DNA
genome (or what’s left of it).
• Each mitochondrion contain 2 to
10 mtDNA molecules, and each
cell has many mitochondria.
Features of the mitochondrial genome
• A circular DNA molecule
• Not bound by a nuclear envelope
• Not packaged into chromatin
• Contains little non-coding regions (no introns- has a
bacterial ancestor)
• Human mtDNA contains 16,569 base pairs with encodes
for 13 proteins, 22 tRNAs and 2 rRNAs.
The ‘story’ in mtDNA
• mtDNA is inherited only
through the maternal line
allowing the tracing of direct
genetic descent free of
recombination.
• All the mitochondria in your
cells are clones of your
mother! Whereas genes in
nuclear DNA are inherited
from both parents.
• We can be more certain about
the inheritance of mtDNA.
Comparative Genomics
• The study of the relationships between the
genomes of different species.
• We can identify relationships by comparing
the fraction of shared genes between species.
• The greater the degree of shared genes the
more closer is the relationship.
The big picture
• http://www.sumanasinc.com/webcontent/ani
mations/content/evolution/evolution.html
Good summary of evidence for evolution
Evolution
Divergent Evolution
• Closely related species
become more
dissimilar over time, in
response to different
selection pressures.
• Adaptive radiation is
when a variety of
different species evolve
from a single ancestral
species.
Adaptive Radiation
• The process whereby
organisms with a
common ancestor
develop adaptations
in response to
environmental
pressures (e.g.
changed food source)
Convergent Evolution
• Over time selection
pressures may act on
distantly related
species to produce
similarities called
analogous structures.
• It appears the different
species are becoming
more similar.
Echidna
Depicting Relationships
• Phylogeny is the study of evolutionary
relationships between species.
• These relationships are depicted in a
branching diagram called a cladogram or
phylogenetic tree.
Depicting Relationships
• The diagram is based on discovering shared advanced characteristics
for each branch point.
• All the species at a particular branch point share a common ancestor.
A cladogram
Constructing Phylogenetic Trees
• The use of the term “tree” has
given rise to terms to describe
the different parts of the
diagram.
• Branches terminate in a leaf
(single species). Adding branch
lengths can give an indication
of evolutionary time since a
divergent event.
• Nodes represent a branching
point where two or more
species diverged from a
common ancestor.
Change can be gradual over time
The theory of
evolution by natural
selection is based
upon slow gradual
change within a
species over time.
Change within a
species is termed
micro-evolution.
Change can be punctuated over time
Another model has been
proposed for macro-evolution.
The “Punctuated model”
proposes that species persist
unchanged for long periods of
time that is then punctuated
by short intervals of rapid
evolutionary speciation.
Somewhat supported by the
fossil record.