1. Evidence for Evolution

2. Evolution
“the gradual change in the characteristics of a species over many generations”

3. Evidence People still do not believe it
Evidence must be provided in support
2 types of evidence
Fossil
Comparative studies

4. Fossils
A fossil does not have to be a part of an organism. Any preserved trace left by an organism that lived long ago is a fossil. Fossils may therefore include footprints, burrows, faeces or impressions of all or part of an animal or a plant, as well as bones, shells or teeth.

5. Evolution of the Horse

6. Fossil Formation Very rare
may become fossilised when they are buried by drifting sand, mud deposited by rivers, volcanic ash or by other members of the species.
soil is very important
In wet, acid soils minerals in the bone dissolved and no fossilisation occurs. However, if this soil contains no oxygen, as in the case of peat, complete preservation of the soft tissues of the animal as well as the bones may occur.
Alkaline soils produce best fossils as minerals in bones are not dissolved. New minerals, often lime or iron oxide, are deposited in pores of bone, replacing organic matter that makes up about 35% by weight of the bone. The bone becomes petrified (turned into rock) but the details of structure are still preserved

7. Dating Fossils Absolute- actual age Relative- older or younger
Potassium Argon Dating
Carbon 14/ Radiocarbon dating
Tree ring dating/ dendrochronology
Relative- older or younger
Stratigraphy
Fluorine Dating

8. Potassium Argon Dating
Based on the decay of radioactive potassium to form calcium and argon.
Isotope potassium-40 is radioactive and decays to form calcium-40 and argon-40.
Decay takes place at an extremely slow but constant rate
has limited usefulness: can only date rocks older than to years.

9. Carbon 14/ Radiocarbon Dating
based on the decay of the radioactive isotope of carbon, carbon-14, to nitrogen
Half life of /+ 40 years
After about years, quantity of carbon-14 left is negligible thus radiocarbon dating cannot be used to date back more than about years.
A further limitation is that the material to be dated must be of organic origin,that is, it must contain carbon.

11. Radioactive Decay of Carbon 14
Half life of /+ 40 years

12. Tree Ring Dating/ Dendrochronology
Concentric rings on the surface of a cut tree trunk.
Each ring represents one year’s growth
Rings differ in width according to how favourable the growing season was.
Marker rings

14. Tree Ring Dating/ Dendrochronology
The bristle cone pine, which grows in the Sierra Nevada in the United States, has been of great value in tree ring dating. By taking sample cores from the trunks and counting growth rings, some of the living trees have been found to be over 4500 years old. By correlating marker rings in these trees with those of dead pines, accurate dates as far back as 8600 years ago have been established. It has been possible to use wood

15. Tree Ring Dating/ Dendrochronology

16. Stratigraphy Study of layers or strata Two ways it can be applied
principle of superposition
correlation of rock strata

17. Principle of Superpositon
assumes that layers of sedimentary rock the layers at the top are younger
than those beneath them.
Thus, any fossils or other material found in the top layers will be younger than material found lower down (Fig. 17.9).
This principle must be applied with care- distortions of the earth’s crust occur and it is possible for fossils or artefacts to be buried by animals

19. Correlation of Rock Strata
matching layers of rock from different areas.

20. Fluorine Dating
When bone is left in soil, fluoride ions, which are present in the water in the soil, replace some of the ions in the bone itself.
All the fossil bones in a particular deposit should contain the same amount of fluoride, so that fossils that have been displaced can be detected.
The older the fossil the more fluoride it contains, so that the relative ages can be established.
It is not possible to decide absolute ages using this method since the concentration of fluoride in ground water varies from place to place and from time to time.

21. Problems with Fossil Record
For fossils to be formed, four conditions are usually required:
a quick burial of the material
the presence of hard body parts
an absence of decay organisms
a long period of stability—the organism needs to be left undisturbed
So fossilisation is usually by chance

22. Problems with Fossil Record
Very few fossils have been discovered
Unusual to find fossil of entire organism
Dating techniques not 100% accurate

23. Comparative Studies Homologous features *Analogous features
Comparative embryology
Vestigial structures
Phylogenic trees
Genetic Comparisons
Molecular Comparisons
DNA sequencing

24. Homologous Features Fundamental similarity or structure
Land plants- seeds of cycads, Ginkgo, conifer trees and flowering plants show a variety of shapes and sizes but they are the same basic structure
Mammals- classic examples is the forelimb of vertebrates.
The same bones appear in various forms throughout the vertebrates—the feet of amphibians and reptiles, the wings of bats and birds, the leg of a horse, the flipper of a whale or seal, and the human hand.
bones are arranged in a similar way, even though some have developed different functions.
Organisms possessing organs that are similar in structure are likely to have a common ancestor. Therefore, the arrangement of the bones of the forelimb in such a range of vertebrates is convincing evidence that they have all evolved from a common ancestor.

26. *Analogous Features Serve same function but have evolved separately
Must distinguish between Analogous and Homologous

27. Comparative Embryology
von Baer’s law- features common to all members of a group of animals are developed early in the embryo and that more special features, which distinguish the different members of a group, develop at a later stage of development

28. Comparative Embryology
Vertebrates-Dorsal brain and spinal cord, axial skeleton, gill or pharyngeal slits, and aortic arches develop early.
Special features like fins, fur or feathers, which distinguish classes, develop later

30. Vestigial Structures
Reduced structure with no apparent function but is evidence of evolutionary relationships
The pelvic bones of whales are reduced and functionless
She-oaks have small, brown scales that have no obvious function but are considered to be reduced leaves

31. Phylogenic Trees
Based on the sharing of homologous features, is a branching diagram showing how organisms are related and how they have diverged during evolution
“phylogeny”- the pattern of how organisms are related through evolutionary descent from a common ancestor