1. NATURAL SELECTION & EVOLUTION

2. Natural selection The survival of organisms that are best suited to surviving and reproducing in their environment Change in a population over a large number of generations that may result in the formation of new species which are better adapted to their environment Evolution

3. Evidence of evolution Most of the evidence for evolution comes from rocks and fossils. Sedimentary rocks are made up of deposits of organic and other material, laid down over hundreds of thousands of years. Organisms are buried in between the layers and their remains may eventually be preserved as fossils. Ammonites became extinct about 65 million years ago.

4. Fossils can be formed in either of two ways: Some are stone copies of the organism, formed as the organism becomes petrified by the deposition of minerals in the tissues as they decompose. Other fossils consist of impressions of the organism's shape, left behind in the surrounding stone as the tissues decompose. Most fossils are of the hard parts of the organism which take the longest time to decay - such as bones and teeth in animals and hard, lignified tissues in plants.

5. Most dead organisms decay very rapidly and their tissues are recycled, leaving no trace of their existence. But certain environmental conditions drastically slow down the decay process, thus helping to preserve the tissues e.g: Insufficient oxygen - for example when an organism becomes trapped in resin, which eventually turns into a hard, impervious material called amber Low temperatures - for example when an organism becomes frozen in a glacier High soil acidity - for example when an organism is sucked down into a peat bog

6. The Fossil record Fossil remains have been found in rocks of all ages Fossils of the simplest organisms are found in the oldest rocks and fossils of more complex organisms in the newest rocks This supports the evolutionary theory that simple life forms gradually evolved into more complex ones, and that all animals have gradually evolved from a common ancestor However it's not always as simple as it sounds. Rocks move around, so you don't always find the newest rocks near the surface, or the oldest rocks deep down. Nor is evolution always an orderly progression from simple to evermore complex - it goes in fits and starts

7. The Horse One of the few animals for which we have a fairly complete evolutionary record is the horse. All the main stages of horse evolution have been preserved in fossil form. Over 60 million years, the horse evolved from a dog-sized rainforest-dwelling creature into an animal adapted to plains- dwelling and standing up to 2 metres high. In the process it traded in its multi-toed feet, adapted for walking across the forest floor, for single-toed hooves, suited for running over open country.

8. Extinction Of course sometimes species or whole families of organisms die out or become extinct (remember the dinosaurs!) There are many endangered species threatened with extinction now, and many more will soon become extinct unless humans take steps to protect them.

9. Extinction An increase in the number or efficiency of predator species. A failure to compete successfully (e.g. for food or space) with other species in the same habitat. Rapid climatic or other environmental changes. Natural catastrophes (e.g. fires or floods) which wipe out habitats. The impact of new diseases to which the species has no immunity. Impact of man Any of the following factors can contribute to the extinction of a species:

10. An example of extinction The Dodo was a large flightless bird first observed by European visitors to the Indian Ocean island of Mauritius around 1600. Mauritius was colonised by the Dutch, who overhunted the bird for food, damaged its forest habitat and introduced other species, like pigs, cats and rats that ate the Dodo's young and eggs. Within eighty years the Dodo was extinct - entirely as a result of the activities of man. a kind of flightless pigeon weighing up to 22 kilos The Dodo

11. Extinction In fact today it is our activities that constitute the greatest threat to the survival of other species on our planet.

12. Darwin’s theory of evolution Charles Darwin (1809 - 1882) was an English naturalist who made a study of variation in plants and animals during a five-year voyage around the world in the mid-19th century. Although he was not the only scientist working on evolutionary theory - Alfred Wallace was coming to the same conclusion around the same time - it was Darwin who published his ideas first. ‘On the Origin of Species’, which came out in 1859, is possibly the most influential scientific book ever written. Charles Darwin 1809-1882

13. Darwin made four important observations: All organisms produce far more offspring than could possibly survive to maturity Within a species, population numbers tend to remain fairly constant over long periods of time Organisms in a species show wide variation due to different genes Some of the variations are inherited and passed on to the next generation

14. and then made these two deductions: Since most offspring don’t survive, all organisms must have to struggle for survival, i.e. we are in continuous competition with each other for food, mates, access to space etc. The ones that survive and reproduce, i.e. ‘the fittest’, will pass on their genes

15. The theory of evolution and scientific debate The theory of evolution of species undermined the religious belief in creation - the idea that God had made the earth and everything in it, just the way it is today. The thousands of millions of years necessary for evolution to take place contradicted current thinking about the age of the earth, which most scientists thought was only tens of millions of years old at most. When Charles Darwin proposed his theory of evolution over 150 years ago it was deeply controversial. Many people, including other scientists, were shocked or bitterly hostile to the idea. This was because:

16. The theory of evolution and scientific debate The idea that species had evolved from earlier, different species contradicted people's instinctive assumption that organisms had always been the way they are now - that only apes can develop from apes and only humans from humans. The idea that humans were not created humans and could be related to some 'lesser' species was distasteful to some and considered blasphemy by others. Charles Darwin 1809-1882

17. The Peppered Moth White and black peppered moths are a classic example of natural selection in action Before the industrial revolution in Britain, most peppered moths were of the pale variety. They were well camouflaged against the pale birch trees that they like to sit on. Moths with the mutant black colouring were easily spotted and eaten by birds - giving the white peppered variety an advantage.

18. The Peppered Moth Then the industrial revolution came along in the 19th century … Airborne pollution in industrial areas mottled the birch tree bark with soot. Now the mutant black-peppered moths blended better against the darkened bark, while the white variety became much more vulnerable to predators. Over time the mutant black-peppered moths were naturally selected to survive and became far more numerous in urban areas than the pale variety.

19. The Galapagos finches The Galapagos finches showed wide variations - e.g. in beak shape and size - from island to island. Darwin deduced that these differences made the finches better adapted to take advantage of the food in their particular local environment Thin, sharp beaks prevailing where the birds' main food was insects and grubs. Large claw-shaped beaks where their diet was buds, fruit and nuts. In each locality the finch population had somehow developed beaks which were suitable for that particular environment. Darwin's drawings of variant heads and beaks among Galapagos finches

20. The Galapagos finches In each locality one or more individual finch happened to acquire, by random mutation, a beak shape more suitable for the food sources in that locality. These individuals then had a competitive advantage over their fellow finches, enabling them to grow and reproduce more successfully. They pass on their more specialised beaks to successive generations - until eventually the characteristic had spread throughout the finch population in that locality. Darwin's drawings of variant heads and beaks among Galapagos finches Darwin concluded:

21. Antibiotic-resistant bacteria Simple organisms like bacteria and viruses show us examples of evolution in a very short space of time as they reproduce rapidly. By doubling their numbers every 20 minutes they can produce several generations in a few hours and therefore evolve in a relatively short time. One example is the bacterium E.coli., which can grow and multiply rapidly in nutrient agar. E.coli bacteria

22. Antibiotic-resistant bacteria VARIATION During replication their DNA can be damaged or changed (mutation). Most of the time this results in death, but occasionally the mutation is beneficial e.g. resistance to the antibiotic, penicillin. COMPETITION When antibiotics are poured onto the agar plate, all bacteria will die except the ones with the beneficial mutation.

23. Antibiotic-resistant bacteria BEST ADAPTED The penicillin-resistant bacteria survive and reproduce. PASS ON THEIR GENES More bacteria are becoming resistant to penicillin. This is a major health issue.