Was Darwin Wrong?

{draw:g} {draw:g} {draw:g} Table of Contents Introduction Who was Charles Darwin? Charles Darwin was born in 1809 in Shrewsbury, England. Originally, Darwin did not believe in the idea of evolution and trained to be a priest before studying geology and biology. In 1831, when Darwin was 22, he set sail around the world on HMS Beagle, a naval survey ship. The trip lasted for 5 years during which time the ship stopped at many places including the Galapagos Islands, just off the west coast of South America. Darwin examined animals and plants from everywhere he visited, taking specimens back to England and recording his observations in a diary. However he was most intrigued by the finches on the Galapagos Islands†¦ What was Darwin’s Theory of Natural Selection? {draw:frame} Darwin noticed that there were wide variations in the finches’ size, beaks and claws. He decided the beaks were designed for eating different things and concluded that the finches must have evolved from just one species which had changed over time. They had adapted to their surroundings. In order to begin to understand natural selection, it is important recognise how the many hundreds of thousands of living organisms are classified. The diagram on the next page shows an example of how we determine a species. {draw:frame} {draw:rect} A species can be defined as a group of organisms so similar they can breed together to form fertile offspring. For example, a horse and a donkey can breed to produce a mule but the mule, is infertile therefore showing a horse and a donkey are of different species. Within a species there are still differences and this variation is very important in evolution because without them, natural selection could not occur. Variation can be either genetic, environmental or a combination of both. For example: Variation caused by genes includes eye colour , gender Variation caused by the environment includes accent Variation caused by a combination of both includes high blood pressure, weight Nearly all variation is caused by a combination of these factors. Many people before Darwin thought about evolution and most scientists agreed that life on earth started from a few, simple living things. Alfred Russel Wallace and Jean Baptiste de Lamarck both had ideas about evolution, but Darwin was the first to come up with a plausible idea of how evolution happened. This is what he called Natural Selection and when he returned from his round the world trip, Darwin spent over twenty years working to prove his theory. Wallace wrote to him asking him for advice and together they wrote a paper about evolution. To summarize, Darwin’s theory is basically: Species change over time. This is supported by the fossil record. All organisms share a common ancestor which explains the similarities between organisms that are classified together. This is supported by evidence of vestigial organs and homologous structures (see page 6). Evolutionary change is gradual and slow. This is also supported by the fossil record. Another crucial conclusion Darwin made, was that there are always going to be too many of one species for each of them to survive. This is because they will always be in competition for food and space. He established that those best suited to survive pass their genes onto their offspring, which causes their species to change over time and could lead to their extinction. {draw:frame} {draw:frame} {draw:rect} {draw:frame} {draw:rect} {draw:rect} {draw:frame} {draw:frame} {draw:rect} Diagram to show the steps in natural selection Why the population of a species changes over time {draw:frame} In the above graph, the Canadian lynx eats the Snowshoe hare. No other cat is so dependent on a single prey species. Two years after a rise in the snowshoe hare population, there is a rise in the lynx population. Then, the Snowshoe hare population falls. When there are too few Snowshoe hares for the lynx to survive, their population starts to fall as well. Because the predator population has now decreased, it allows time for the prey population to increase again. As there is now more food, the predator population starts to increase again. This cycle repeats itself over and over. That is why we say there is a clear pattern of interdependence between the two populations. What Evidence did Darwin Use? Fossil Record A fossil is a dead plant, animal or other once-living thing that has been preserved for millions of years and leaves an imprint in stone. Almost all fossils are from extinct species. Darwin used fossils to prove that evolution happened. He could determine the relative age of various fossils by looking at the layers in the rock and he could see the changes in one type of fossil. For example, by collecting many fossils of one animal, he could see how it had evolved over time. An animal may become extinct when there is a sudden change in their habitat – for example food or temperature. A new species can become either the predator or the prey of a species already living there, thus placing either species under possible threat of extinction. The extinction of a species has an effect on the food chain. Limitations of the Fossil Record There are gaps in the fossil record because the conditions were not always suitable for fossils to develop. This meant that not every species was recorded as a fossil and sometimes a species would occur that had no link to a previous one. Also, because evolution happens over a long period of time and often in sudden bursts, (these bursts could be up to 10,000 years apart) evidence of smaller changes were not recorded. Vestigial Organs A vestigial organ is one that has little or no use now, but was well developed in its ancestors – exactly like our appendix. By looking at vestigial organs in modern species and seeing if older species had used that organ, Darwin could determine how a species had changed over time. Homologous Structures Darwin also compared homologous structures which are body parts that structurally similar in related species. If two or more different species have homologous structures, it shows that they have come from the same origin. For example, gorillas and homo-sapiens both have similar body features (hand, skulls†¦ ) illustrating that the two species have the same ancestors. Was Darwin’s theory accepted at the time? Darwin’s theory was widely rejected at the time because many people were creationists. This means they believe the creation story in the bible i. e. ll life was created in six days. Darwin’s theory of evolution challenged this view, but because there were gaps in the fossil record, it was hardto trace the changes in a species and convincing people, therefore was very difficult. Also, the age of the earth was estimated by using the Bible to be about 6000 years old, but this did not seem long enough for evolution to have taken place. Finally, although Darwin knew certain features were passed on from generation to generation, he could not explain why (see later). What other theories were there? Lamarck’s theory Lamarck had a different theory. He believed that by striving to fit into their surroundings, the animal’s bodies changed. According to his theory, the giraffe developed its long neck by stretching it to reach the leaves on trees. Similar to other scientists he explained that life started with simple living things. However, he believed that at each generation, they became more complicated. His theory did not take account of the single celled life that still existed on Earth. Lamarck could see the changes in a species, but tried to explain it in a different way because he was afraid that people would not support the idea of natural selection. Mendel’s theory George Mendel was born in 1822. Because he was poor, he joined a monastery, but also studied at the University of Vienna where he learned to carry out scientific experiments. At the monastery he learned how to breed plants and one of his jobs was to create better varieties. He was very interested in how features were passed on from one generation to the next and he decided to crossbreed different pea plants to see what would happen. He crossed red flowered plants with white and the resulting plants were all red. He then bred these plants together and this experiment returned mostly red but some white. Mendel concluded that there must be different versions of the same genes. What evidence has been obtained since Darwin? Peppered Moths – Kettlewell studies of the 1950’s During the industrial revolution, carbon (soot) coated trees in a dark colour. The once dominant and well camouflaged pale moths (typica) were now being replaced by the rarer darker moths (carbonaria). These moths continued grow in numbers and by 1895 they represented 98% of all moths in Manchester. Naturalists at this time suggested this was a result of the industrial activity on the local landscape and that the darker moths had a survival advantage. They had become so well camouflaged on trees they had stopped being eaten by birds, whereas the paler, typica species had now become clearly visible. The general population had changed from the pale coloured moth, to the darker coloured moth and this was another example of natural selection. In 1998, a scientist called Michael Majerus re-examined Kettlewell’s studies and concluded that the colour change in the moths is an example of natural selection, but predation by birds is only one factor – not the sole factor. DNA (Deoxyribonucleic Acid) and Genetics Francis Crick, a scientist from Cambridge announced in 1953, he and James Watson had found the â€Å"secret of life† – the structure of D. N. A. D. N. A. is the material inside the nucleus of cells and carries the information of how organisms develop. It is copied when new cells are made, but can be damaged or changed, usually resulting in the death of the cell. Genes are passed on from parents to offspring ensuring that the most successful individuals survive. Variation is caused because of differences in genes. Bacterial antibiotic resistance Sometimes a mutation in D. N. A. can be beneficial for the bacteria. For example bacteria can become resistant to antibiotics and this gives them an added advantage over non-resistant bacteria. Why I think that new evidence will continue support Darwin’s theory I think that new evidence will continue to support Darwin’s theory for a number of reasons: Advances in technology mean newer ways of discovering the past will become available As species evolve further, scientists will have etter records to get information from Now scientists know what they are looking for which provides evidence of evolution Overall, I agree with the scientific belief today that â€Å"natural selection is the mechanism which leads to adaption and diversity† whilst â€Å"genetics provide the mechanics for traits to be inherited† Bibliography