Evolution
Evidence for Evolution
What is Evolution??
• Change in the genetic composition of a
population during successive generations, as a
result of natural selection acting on the
genetic variation among individuals, and
resulting in the development of new species.
24 hour clock analogy
• It’s midnight on a clock.
• At 5 in the morning, life begins, with bacteria, 3.5
billion years ago.
• The Jurassic Period, which was 250 million years
ago, would be 10.40pm.
• The apes appeared on Earth at around 11.55pm.
• First humans, 2.5 million years ago, appeared at
11.59pm.
• Your lifetime would be around 1/3000th of a
second in that 24hr clock.
Evidence of evolution through fossils
• Fossil is the preserved evidence of life from
the past.
• Direct evidence or Indirect evidence
• Direct Evidence
• Fossilised bones (which are actually rock),
mould and cast.
Cast
Evidence of evolution through fossils
• Indirect Evidence
• Anything from life from the past, but not
direct. E.g. paintings, footprints, droppings,
tools.
How Fossils Form
• Fossils form in sedimentary rock (rock made
from sand or silt or mud).
• These form layers at the bottom of a lake or
ocean or river. These layers get compressed
and as this happens the sediments get hot,
the sand then fuses to form new rock.
• It’s in those sedimentary rocks that fossil form.
Almost always under water.
Fossilised Bones
Fossils Forming
• For a fossil to happen, there are three main
conditions necessary.
• 1. Once the specimen dies, it needs to be covered
very quickly by sediment (usually under water).
• 2. The decay of that organism needs to be
prohibited by the exclusion of oxygen by the
sediments. Best when conditions are dry, cold or
acidic. When sediments are packed around that
organism, it stops bacteria from getting to it.
• 3. Must be left undisturbed for millions of years.
What Fossil Records Show Us
• 1. Species disappear over time. Eg dinosaurs.
• 2. That some species weren’t around, but
now are. Eg. humans, previous to 2.5 million
years ago there have been no fossilised
evidence of humans.
• 3. Trend towards complexity as we go from
older rocks to younger rocks. E.g. Bacteriaeukaryotes, Fern-flowering plants, reptilesbirds.
What Fossil Records Show Us
• 4. Fossils, which are those that are half way
between reptiles and birds. Most classic
example is a reptile/bird called archaeopteryx.
Reptile/Bird Archaeopteryx
Problems With Fossils
• Fossil records are not quite complete. Some
species are not well represented and most
fossils are incomplete.
• COMMON EXAM QUESTION!
• Most animals that die do not get fossilised,
they just decay.
• Forming fossils is very rare.
• Lots of environments aren’t conducive to
making fossils. Eg Mountain Goats
Problems With Fossils
• Fossils get destroyed easy, by movement of
sediment.
• Some species have behaviours that aren’t
conducive to forming fossils. Eg apes
• Soft bodies. E.g. worms
• On the planet for a short period of time.
• Evolved and then become extinct.
• Not very wide spread. Eg cheetahs
Biogeographical Evidence for
Evolution
•
•
•
•
Biogeography is the study
of the distribution of
animals and plants
across the earth.
Progression
• 250 million years ago, all the continents of the
earth were joined in one land mass called
Pangaea.
• 11 o’clock pm, Pangaea broke up to form
Gondwana in the south and Laurasia in the
north.
• At about 11.12pm, Africa separated from the rest
of Gondwana and then the rest of Gondwana
continued to break up until 11.39pm.
Examples of the Effects
• Large, flightless birds (Ratites), only seen in
the south.
• Waratahs only seen in Western Australia,
closely related to the Proteas of South Africa.
• Mistletoe only native in the north (northern
America and across Europe.
• Wattles only seen in Australia and Africa.
Ratites
Ratites
Closely related
• Waratah
• Proteas
Marsupials
• Very few Australian animals that aren’t
marsupials, only bats and rats, rest of the world
doesn’t have marsupials (except one).
• Marsupials were around before placental
mammals.
• Placental mammals evolved in the northern
continent after Australia had broken up from the
rest of the world.
• As the placental mammals spread across the
world, they killed off the marsupials, but they
couldn’t get to Australia.
Marsupials
Australian Megafauna
•
3m Kangaroo
• Marsupial Lion
Australian Megafauna
• Giant Wombat
•
Size of a 4 wheel drive
Anatomical Evidence of Evolution
• Two main kinds of evidence of evolution from
anatomy: homologous structures and
analogous structures.
• But there is also vestigial structures.
Homologous Structures
• When species share a common ancestor, so have
similar structures, even though they may be used
for completely different things.
• Example: pentadactyl limb of vertebrates.
• In our arm we have one upper arm bone, then
two lower arm bones, then we have our wrist
bones or carpals, then five fingers (phalanges).
• When you look at other mammals, you find this
same basic design, even though some may use
them for different means.
Homologous Structures
• A dog has the same basic design, but they use
them for walking on.
• A bat uses their fingers to hold out a
membrane that they use to fly with.
• Whales have the same basic structure in their
flippers to swim.
Pentadactyl Limb
Homologous Structures
• Different functions but same basic structure.
• All evolved from the same common ancestor.
• Kind of evolution that leads to homology is
called divergent evolution (process where by
organisms with a recent common ancestor
develop different adaptations in different
habitats).
What’s wrong with Pegasus then?
Analogous Structures
• Features of different species, which have the
same basic function, but completely different
structure.
• Have not been derived from a common
ancestor.
• Have evolved in response to a similar
environment.
Analogous Structures
• Eg sharks dorsal fin and dolphins dorsal fin.
They are not closely related, but both have
dorsal fin.
Analogous Structures
• Eg the wings of a pterosaurs, bat and bird
Vestigial Structures
• A structure found in a species, which is not
being used as it is in other species.
• A structure that is left over from the past,
which was once useful, but no longer is.
Vestigial Structures
• Eg pelvis of whales.
• The use of a pelvis is to support our spine on
top of our legs so we can walk.
Vestigial Structures
Vestigial Structures
• E.g. blind cave fish
Vestigial Structures
• E.g. python with legs
Molecular Study for Evidence of
Evolution
• Compare the DNA of two different species.
• If two species have evolved from a common
ancestor, you would expect that their DNA
would be similar.
• Eg A human and chimpanzee
Molecular Study for Evidence of
Evolution
• E.g. A human and chimpanzee
Molecular Study for Evidence of
Evolution
• If you compare two organisms that look the
same, but are distantly related, like sharks and
dolphins, you see that there is a great deal of
difference between their DNA.
Genetically these two are completely
different!
sugar glider
Rocky and Bullwinkle
• size, colour, black stripe down back, all similar,
• but DNA comparison will show that sugar
glider is more similar to a kangaroo than it is
to the DNA of a flying squirrel.
• Sugar Glider and
• Flying Squirrel