1. Evolution

2. 2 Contents Definition Darwin & Wallace Darwin & Wallace Natural selection - the observations Natural selection - the observations Natural selection - the conclusions Natural selection - the conclusions Evidence to support evolution Anatomy Embryology Biochemistry Cytology Physiology

3. 3 Evolution is about how modern day plants and animals have gradually developed from pre-existing forms, over long periods of time i.e. changes in species by natural selection in response to environmental changes i.e. survival of the fittest.

4. 4 Darwin & Wallace Many scientists had stated that species must have evolved from one another. Charles Darwin (1809 – 1882) – first to suggest a mechanism or theory for it to happen – did not publish his theory. Sixteen years later Alfred Wallace came up with the same theory. The mechanism is called natural selection. Based on four observations and two conclusions.

5. 5 Natural selection – the observations 1. Individual members of a species are different from one another. 2. Offspring resemble their parents (variation is inheritable). 3. More offspring are produced than can survive and reproduce. 4. There is a struggle for existence and some individuals have variations that make them better suited to survival than others.

6. 6 Natural selection – the conclusions favourable variations may make individuals more adaptable favourable variations may make individuals more adaptable – these variations are passed on genetically and will eventually become the norm. => survival of fittest. successive variations accumulate and successive variations accumulate and eventually interbreeding between this and the original organism is no longer possible. =>new species formed.

7. 7 Evidence to support evolution (1/2) The evidence shows that there was a common descent between different groups of organisms or that different organisms share a common ancestor. The evidence comes from a number of sources: - Fossils – Palaeontology Fossils – Palaeontology Geographical distribution Geographical distribution Taxonomy and Taxonomy and

8. 8 Evidence to support evolution (2/2) from the comparative studies of: - Anatomy Anatomy - Embryology Embryology - Biochemistry Biochemistry - Cytology Cytology - Physiology Physiology

9. 9 Comparative anatomy The forelimbs of terrestrial vertebrates are similar in structure - the basic structure is known as the pentadactyl limb. The forelimbs share the same basic structure but differ in their functions:

10. 10 Structures that differ in function human - lifting and grasping rabbit - leaping whale fin - swimming ant eater - tearing bat wing - flying monkey - grasping mole - digging horse - speed

11. 11 The pentadactyl forelimb in a number of vertebrates

12. 12 Vestigial structures Some structures have been lost – they no longer serve a function. e.g. horse stands on its third toe. Toes two and four are present in a vestigial form. One and five are no longer present. Back to Evidence to support evolution

13. 13 Comparative embryology The study of developing embryos of vertebrates shows a similarity between certain structures e.g. the position of the brain, eyes, gill slits and tail of the fish, tortoise, rabbit, bird, chick and human. This suggests that organisms descended from common ancestors.

14. 14 e.g. gill slits If all vertebrates came from a common ancestor who had gills, it would be likely that all vertebrates would develop gills and then modify them into other structures. This is exactly what happens.

15. 15 A comparison of four vertebrate embryos Back to Evidence to support evolution

16. 16 Comparative biochemistry The similarities between the respiratory pathways in all living cells suggest a common ancestor. All living things use DNA, ATP and many of their protein structures are very similar. The greater the similarity in protein structures, the more closely related they are, and the smaller will be the difference in their DNA structure.

17. 17 An evolutionary tree based on similarities in fibrinogen molecules Back to Evidence to support evolution

18. 18 Comparative cytology The presence of organelles such as mitochondria, endoplasmic reticulum and ribosomes in most cells and substances such as DNA, RNA and ATP suggests a common ancestor. Back to Evidence to support evolution

19. 19 Comparative physiology A study of the similarities between blood pigments in the animal kingdom suggests a common ancestor.

20. 20 END Go to PPT on ‘The Evidence for Evolution’‘The Evidence for Evolution’ Contains some very good pictures