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3.3 Speciation and Evolution Think of three different species of bird? What makes them different from each other? We are going to be learning about 1. 2. 3. 4. 5. What is evolution? How does evolution happen? What is and is not a species? How does speciation happen? What evidence is there to support the theory of evolution? Evolution Darwin proposed that natural selection could result in the formation of a new species. He called this ‘modification by dissent’. The term evolution was applied by other scientists. Look at the kingfishers at the top of p85. The Origin of Tetrapods What is a species? Initially the definition of a species was defined if two organisms could interbreed to produce fertile offspring. Male Donkey Female Donkey Species = Donkey Donkey What is a species? Female Horse Male Horse Species = Horse Horse What is a species? Male Donkey Female Horse Species = Mule Not a species – Mule is infertile What is a species? The horse reproduces with other horses to produce more animals of the same species, as does the donkey. However, when they are cross bred they produce a mule. A mule is sterile and cannot reproduce therefore, not a species. Nowadays, scientist compare DNA when comparing species. Speciation Speciation is the process by which one species splits into two or more separate species. Darwin first discovered this by comparing Finch species. Sorting Finch Species Speciation Speciation Occurs by the following steps: 1. Variation 2. Isolation 3. Selection Speciation explained Evidence for evolution - Fossils From the first fossils to later examples it can be seen that organisms become more and more complex. This is expect as new alleles and genes develop from mutation. This eventually leads to speciation. Translational fossils fossils have also been recovered. These show one group of organisms changing to another. Evidence for evolution – Comparative anatomy Comparing the anatomy of living creatures to fossils from that species can tell us about speciation events that have lead to evolution. Try Activity Book 3.5. Evidence for evolution – DNA and protein structure • Many organisms share similar DNA. • The gene in humans that is responsible for cell energy release shares 70% of the same DNA as the gene that does the same job in fungi. • Animals that look the same often have very similar DNA. Humans have 96% of the same DNA as chimpanzees. Evidence for evolution – Distribution of current species Many unique species occur on isolated islands. As the species was originally isolated from its parent species you would expect it to evolve and adapt to its environment. Australia has been isolated from other land masses for 40 million years. This has lead to the evolution of unique species. Evidence for evolution - embryology Embryology - The study of the development and structure of embryos. Vertibrate embryos have structures that appear to be homologous on the basis of anatomy. Summary Create six summary sentences about what you have learned about evolution. Unit Review 3.3 Do Unit review 3.3