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TOPIC 5 Evolution and Biodiversity DARWIN AND WALLACE Charles Darwin, in 1858, traveled on board the HMS Beagle for scientific exploration lasted for 5 years. He saw nature in a new way which became the most important, controversial, and misinterpreted ideas in biology: Evolution by natural selection. Alfred Russell Wallace had independently developed a nearly identical theory. Together in 1858, they presented their ideas to the Linnaean Society. WHAT IS EVOLUTION? Evolution is defined as the process of cumulative change in the heritable characteristics of a population. Cumulative-one change is typically does not have a major impact on a species. Heritable- it must be passed down Population- the change does not affect a single individual. *If enough change occurs in a population, a new species can arise. (This process is call speciation) SPECIATION The new members will be different enough from the pre-existing population that they came from, they can no longer interbreed. *Such a process is rarely observable during a human lifetime. EVIDENCE FOR EVOLUTION BY NATURAL SELECTION. 1) The fossil record 2) Animal breeding 3) Homologous Structures THE FOSSIL RECORD AND EVOLUTION Fossils are the petrified remains or traces of animals and plants. It is the accumulation of evidence from these remains and traces, such as skeletons and footprints. AGEING FOSSILS The age of a rock can be determined by examining differences in the ratios of isotopes. 14C (carbon-14) has a half life of 5730 years. When an animal dies, 5730 years later its bones will have lost half their 14C life. 11,460 will have lost 75%. Important: looking at the ratio of radioactive 14C to 14N, it is possible to determine the age of a fossil. After so many half-lives it is hard to tell how much 14C is left. AGEING FOSSILS 40K (potassium-40) is another radioactive isotope, that has much longer half-live. Formed when minerals in rocks crystallize from magma. Once hardened no more 40K can be added. Used to measure the age of rocks between 100,000 years and 4.6 billion years ago. ARTIFICIAL SELECTION AND EVOLUTION Breeding domesticated animals, for example cattle, horses, dogs, sheep, and pigeons. Breeders can see which characteristics an offspring will have by watching which male mates with which female. Producing more milk, better beef. Over the years breeders have learned how to choose which pair mates, getting the desired genetic characteristics. (Selective breeding) Artificial selection is evidence that evolution is happening, but it is certainly not the driving force of evolution in natural ecosystems. ARTIFICIAL SELECTION EVOLUTION OF HOMOLOGOUS STRUCTURES BY ADAPTIVE RADIATION Homologous anatomical structures which are similar in form but which are found in seemingly dissimilar species. Ex. Five-fingered limb found in animals: humans, whales, and bats. Pentadactyl limbs: “penta” means five; “dactyl” means fingers The shape and number of bones may vary, despite the fact that the specific functions of the limbs may be very different. Darwin explained that homologous structures were not just a coincidence but evidence that the organism in question have a common ancestor. SPECIES DIVERGENCE The process of an evolving population changing significantly enough so that the production of offspring with the original population becomes impossible. *two populations of a species have diverged, and a new species have evolved from an old one. *Both species will then continue on their separate ways. ADAPTIVE RADIATION Similar but distinct species evolve relatively rapidly from a single species or from a small number of species. This happens as variation within a population allow certain members to exploit a slightly different niche in a more successful way. Niche-is a position or role within a community of an ecosystem. ADAPTIVE RADIATION Example: Primates found in Madagascar and the Comoro Islands. Without competition from monkeys or apes, lemurs on these islands were able to proliferate. Large numbers of offspring meant a greater change for diversity. Adaptions: living on land, living in trees, living in lush rainforests, and some survive in the desert. Example: Galapagos finches and Hawaiian honeycreepers Both have a variety of beak shape/size. It is possible, within a species that has a wide geographical distribution, to have measurable differences in DNA. Soil/climate so different that populations adapt to those conditions that are available to them. Genes will be selected for some and against others. (Selective Pressure) Over a long enough period of time the populations are so great that they are no longer the same species. TRANSIENT POLYMORPHISMMELANISTIC INSECTS Different versions of a species within a population. Can be from a result of a mutation. Biston betularia, a moth found in temperate climate. This species can have peppered (grey) color or melanic (black) color. Melanic moths (carbonaria) Melanic is rare <1% of population. Around the 1860s the melanic (carbonaria) form was increasing in numbers. What was happening around the 1860s? The lichen was very sensitive to the air pollutants, killing it. The air was also filled with black soot. The light colored moths were now more easily visible in the lichen free, darken tree branch. Since the significant air quality, the carbonaria population went from 95-100% down to 30% and often at 0%. This changing of colors is an example of transient polymorphism, temporary changes in the form of a species.