1. Evolution and extinction

2. Why have some species of plants and animals died out? How do new species of plants and animals develop? Evolution and extinction

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4. Theory of evolution All species of living thing that exist today (and many more that are now extinct) have evolved from simple life forms that first developed over three billion years ago.

5. Evidence for evolution - fossils What are fossils? –The remains of plants and animals from many years ago. –Found most often in sedimentary rocks. How do fossils provide evidence for evolution? –Fossils of extinct animals and plants can be arranged in a time sequence. –This allows inferences to be made about how and when they evolved.

6. Fossils in the Grand Canyon The sedimentary rocks of the Grand Canyon are hundreds of millions of years old. The Colorado River has cut a gorge through the rock 1.6 km deep. Rocks at the bottom of the gorge are 2,000 years old. Observation of the fossils in the rock layers suggests: –fish were the first vertebrates to appear 500 million years ago. –reptiles appeared about 300 million years after the fish.

7. Fossil formation Fossils can form in the following ways: 1.When parts of the plant or animal have been replaced by other materials as they decayed: petrifaction –being converted to stone or a stony substance. 2.Preserved traces of plants and animals: footprints burrows rootlet traces.

8. Fossil formation (continued) 3. Hard parts of animals that do not decay: bones, horns, teeth, tusks. 4.Parts of animals and plants that have not decayed because of unsuitable conditions: mammoths trapped in ice –too cold for decay. bog men found in peat –too acid for decay. mummified remains –too dry for decay.

9. Evidence for evolution - geography What is Continental Drift? – The slow separation of continental land masses as they move on tectonic plates. How does this give evidence for evolution? –Africa and South America have separated. –Some animals on these continents are similar but different; suggesting common ancestors. camelllama lionjaguar rhinocerostapir

10. Evidence for evolution – comparing anatomy What are homologous structures? –Parts of bodies that have similar structure but are adapted to different jobs. Example of a homologous structure: –The pentadactyl (five-fingered) limb amphibians - flippers reptiles – legs and claws birds - wings mammals. whale – flipper human – hand bat – wing.

11. Gene mutations What is a gene mutation? –Changes to a gene caused by changes to the structure of the section of DNA molecule that makes up the gene. What causes gene mutations? –Mutations occur naturally –The chance of a mutation occurring is increased by exposure to: radiation from radioactive materials X-rays or ultraviolet light some chemicals.

12. Mutations in reproductive cells What is the effect of a mutation in an egg or sperm cell? –As the foetus develops after fertilisation it may develop abnormally or die at an early stage in development. Is this kind of mutation always harmful? –Some mutations have no obvious effect. –Occasionally a good mutation occurs that gives an organism some advantage in the struggle for survival. –This good gene may be passed on to offspring.

13. Mutations in ordinary body cells What is the effect of a mutation in an ordinary body cell? –The cell in which the mutation occurred may start to multiply out of control. –Some of these cells may then break away and invade other parts of the body. –This is cancer. This is caused by exposure to: – Radiation from radioactive materials. – X-rays or ultraviolet light. – Some chemicals, particularly those in cigarette smoke.

14. Darwin’s theory of evolution Charles Darwin (1809 – 1882) suggested: –Life is a struggle for survival competition for food threats from predators disease climate changes. –There are continual changes taking place within a species (ie variations between individuals) caused by: reshuffling of chromosomes during sexual reproduction mutations.

15. –Some individuals have variations that give them an advantage over others within their species. –So in the struggle for survival these individuals are more likely to survive to be able to reproduce and pass on their advantageous genes to future generations. –Nature selects the fittest organisms within a species and rejects the less fit. survival of the fittest / natural selection. –So good mutations help evolution. Darwin also suggested:

16. Lamarck’s theory of evolution Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamark (in 1809) suggested: –Parts of the body that are used a lot become well developed. –These beneficial characteristics, developed during an individual’s lifetime, could be handed down to offspring. This suggests that giraffes have long necks because individuals in each generation have stretched their necks a little more during feeding.

17. Mutant microbes and antibiotics What are antibiotics? –Safe chemicals introduced into the body to kill bacteria. Why are doctors reluctant to use them on too many patients? –Bacteria produce new generations very rapidly because of fast reproduction. –Therefore, there is a higher rate of gene mutations. –Chance mutations may result in the formation of resistant groups of bacteria.

18. Extinction What causes the extinction of a species? –Evolution is a slow and gradual process of adapting to change. –Extinction occurs when environmental changes occur too quickly for gradual evolutionary changes to take place, such as: sudden climate changes pollution pesticides and herbicides disease introduction of a new, more successful species into an area.