1. Evidence For Evolution

2. Getting Some Perspective
Planet Earth is about 4.6 billion years old.
Life first appeared well over 3 billion years ago.
The oldest traces of life found so far are about 3.4 byo.
The first animals appeared about 1 billion – 600mya.
Most of today’s animal groups occurred in the Cambrian Explosion about 550mya

3. Getting Some Perspective
Mammals came into existence about 200mya.
Our genus Homo appeared about 2.5mya.
Gondwana was the supercontinent about 200mya.
NZ separated from Aus abouy 80mya
25 – 30 mya NZ was almost completely submerged and existed only as a chain of small islands.

4. Getting Some Perspective
About 10mya sea levels dropped and NZ was one large island.
Sea levels rose and formed the Manawatu Straight, splitting NZ into North and South about 2mya.

5. Biogeographical Evidence
The distribution of species through geological time shows a distinct pattern.
Tectonic forces have reshaped the Earth’s surface, and once joined land masses are now separated by seas and oceans.
Species present on these ancient land masses became geographically isolated.
Due to differing selection pressures on each land mass, the original species evolved into different, but related species.

6. The Fossil Record
Fossils are the remains of living things – bones, shells, or other parts resistant to decay – or their traces such as footprints or burrows that have been preserved in the rock.
There is overwhelming evidence for the evolution of life on Earth.
Very early life was simple, the earliest fossils are of bacteria and algae.
Organisms change over time. Extinct ancestral forms evolved into modern species.

7. The Fossil Record
Some lineages are surprisingly complete, linking ancient long-extinct species with their modern descendants.

10. Formation of Fossils
Fossilisation requires the normal process of decay to be permanently stopped.
This can occur if the remains are isolated from the air or water and decomposing microbes are prevented from breaking them down.
Most fossils occur in sedimentary rock.
Sediments in the sea gradually cover the dead body on the sea floor and petrify it.

11. The Process A dead animal falls to the sea floor.
Sediment covers the skeleton; other bodies fall to the new sea floor.
Time passes; layers of different rocks form.
Movement of the Earth’s crust folds the rock layers.
Erosion of the rock means that fossils can be seen.

13. Interpreting the Fossil Record
This can be used to establish the relative sequence of events in the past.
Fossils provide a record of the appearance and disappearance of organisms over time.
One of the difficulties with interpreting the fossil record is that there are many gaps in it.

14. Dating Fossils
There are a number of ways of dating fossils, the most commonly used is Radiometric Dating.
These rely on the known rates of decay of a radioactive element – the age of a fossil can be determined by comparing the amount of the “parent” radioactive element with that of the stable “daughter” elements present.

15. Dating Fossils
There are other Non-radiometric techniques that are less commonly used. (pg 167 wkbk)

16. Comparative Anatomy
This is the comparison of body structures in different species.
There are 3 main aspects of comparative anatomy that can be used to provide evidence for evolution:
Homologous Structures
Analogous Structures
Vestigial Organs

17. Homologous Structures
These show similar characteristics resulting from common ancestry.
The common structural components have been adapted to a different purpose in different species.
E.g. pentadactyl limbs

19. Analogous Structures
These have the same function but different ancestry.
These structures evolve because the unrelated species live in similar environments where they face similar selection pressures which favour the same types of adaptation.
E.g. birds and insects have wings.

21. Vestigial Organs
These are organs that have become reduced or have lost their function.
Having no obvious function, vestigial structures are no longer subject to natural selection and remain unchanged through a lineage.
E.g. the tail bones in humans and the wing bones in a kiwi.

23. Molecular Biology
The chemistry, structure and processes of all cells are remarkably similar.
E.g. the ribosomes, proteins and DNA etc are all basically the same.
The conservation of structures and processes across all organisms provides evidence for shared ancestry.

24. Molecular Biology
Scientists can determine the nucleotide sequences of particular genes, if they are found to contain a large number of genetic differences due to mutations, it is unlikely that they shared a relatively recent common ancestor.
Mutations take time to accumulate, so the number of differences can be considered a measure of the passage of time.

25. Mitochondrial DNA Mitochondria contain their own DNA known as mtDNA.
Since mitochondria are outside the DNA, it is not subject to meiosis, therefore the only way for genetic variation to occur in mtDNA is via mutation.
When 2 groups diverge, each accumulates different mutations at a fairly consistent rate.

26. Mitochondrial DNA
The number of mutations present in the mtDNA is proportional to the time since divergence.
At conception, sperm do not pass on any mitochondria, they come from the ovum, so everyone gets their mitochondria and mtDNA from their mother.

27. Y Chromosome Analysis Found only in males.
During meiosis it can only exchange alleles from its very tips due to its small size.
This means 95% of the Y chromosome is conserved and is passed from father to son largely unchanged.
Any changes that occur are the result of mutation. (mutations in modern populations can be traced back to their origin.)

28. Comparative Embryology
The early embryonic stages of all vertebrates are very similar, even though the adults are all very different.