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. Bacteria-eukaryotes, Fern-flowering plants, reptiles-birds.

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