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Ch 14 - Evolution (2) How change occurs History: Jean Baptiste de Lamark first noticed that living things have changed over time. He proposed an evolutionary theory based on 3 reasons for change. QuickTime™ and a decompressor are needed to see this picture. 1. An INNATE urge to BETTER THEMSELVES. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 2. “Use and Disuse” CHARACTERISTICS that were in constant use developed (were AQUIRED) and those that were not used were LOST. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 3. Inherited Acquired traits - traits developed by extra “use” were then passed on to the OFFSPRING QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Lamarck himself conducted experiments where he cut the tails off of mice hoping to eventually produce a generation without any tails. He was not amused, the joke goes, when a colleague noted that the some doctors had been performing that same experiment on infant boys for thousands of years. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Unfortunately, Lamarck was INCORRECT on all three points, and his evolutionary theory was DISPROVED. Charles DARWIN first published the more modern theory of EVOLUTION. His ideas were INFLUENCED by several other scientists’ work: QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. http://evolution.berkeley.edu/evolibrary/home.php http://evolution.berkeley.edu/evolibrary/home.php www.darwinday.org/englishL/life/beagle.html www.darwinday.org/englishL/life/beagle.ht Used by permission of Darwin Day Celebration (at DarwinDay.org), 2006 I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection. —Charles Darwin from "The Origin of Species" http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. 1. Charles LYELL A GEOLOGIST who published “PRINCIPLES OF GEOLOGY “ In this book, Lyell proposed the NEW idea that the Earth was VERY OLD and that it had CHANGED greatly over time. Darwin used this information to formulate his THEORY. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. 2. Farmers and ARTIFICIAL selection. Through SELECTIVE breeding, farmers were able to change their crops and livestock. Darwin first realised that natural VARIATION in the species was the basis for change. ARTIFICIAL SELECTION Teosinte (left) and its modern descendent, corn, a product of artificial selection Individuals with UNDESIRABLE traits were not allowed to BREED, so their specific combination of genes did not get PASSED ON. Those that had DESIRABLE traits were breed - therefore the desirable traits were INHERITED by their offspring. Darwin termed this process ARTIFICIAL SELECTION. Link for artificial selection super cow http://www.youtube. com/watch?v=Nmkj 5gq1cQU: QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 3. Thomas Malthus An ECONOMIST. First noted that the BIRTHRATE was greater than the DEATHRATE in humans. He hypothesized that the only things that would stop the EXPONENTIAL growth of humans would be FAMINE, DISEASE AND WAR. They called this the MALTHUSIAN DOCTRINE. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Darwin noticed that other species also have LIMITING FACTORS that control their population. He wondered what determined which individuals would SURVIVE AND REPRODUCE and which would DIE. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 14.2 - Evolution by Natural Selection Using these concepts, Darwin developed the idea of NATURAL SELECTION. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. “Survival of the Fittest” If you are “FIT” you live and reproduce. If you are not as “FIT”, you do not live or you do not reproduce AS WELL. Peppered Moth Example Before Industrial revolution in England After Industrial revolution (they started burning coal which turned all the tree’s black from the soot) NATURAL SELECTION SCENARIO 1. There is variation in traits 2. There is environmental pressure (birds Like the green ones!) 3. There is heredity 4. End result Variation + differential feeding + Heredity = Natural selection Natural selection 14.3 - Genetics and Evolutionary Theory MUTATIONS: The RAW MATERIAL for natural variation. Changes in our GENES create the initial VARIATION in species. (don’t forget to study DNA STRUCTURE, “de-coding DNA” and MUTATIONS in DNA) Gene Pool Total # OF GENES genes in a POPULATION at any one time SEXUAL REPRODUCTION continues to mix up the gene combinations in GENE POOLs, so there is even more NATURAL VARIATION in the species. Evolution: any change in the relative frequencies of alleles in the gene pool of a population. Before grassmouse population After sodinwas laidyard down E.g. Field back Sandy brown 45 Sandy brown 10 Black 4 Black 4 Specked brown 29 Specked brown 29 WHAT HAPPENED? The specked brown mice had an advantage over the other colours of mice after the sod was laid. WHY? Though the specked brown population did not increase, the number of the “specked brown” allele changed as compared to the others. The RELATIVE FREQUENCY of the “specked brown” allele changed. Therefore, according to the new definition, evolution has occurred. WHICH ONE IS AN EXAMPLE OF EVOLUTION? Beetles on a diet There was a year or two of drought, there were less plants that these beetles can eat. All the beetles have the same chance of survival and reproduction, but because of food restrictions the beetles are a little smaller than the previous generation. Beetles of a different colour 90% of the beetles in the population have the gene for green coloration. A few generations later 70% of the population have the gene for brown coloration. 14.4 Notes: SPECIATION how new SPECIES develops from old ones usually due to ISOLATION. (they aren’t able to get to each other, so they are not able to BREED. ) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. GEOGRAPHIC ISOLATION often leads to REPRODUCTIVE isolation; they are no longer able to produce FERTILE offspring. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. This might even be due to differences in MATING rituals – they might not recognize the “signs”! BIRD OF PARADISE MATING RITUALS FROM PLANET EARTH SEXY? ---> QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Once reproductive QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. ISOLATION occurs, the DIFFERENCES between the two new species often increases. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 5 Steps to SPECIATION 1. FOUNDING Fathers and Mothers. An original POPULATION is established in it’s environment and fills a particular NICHE. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 2. Separation of the Populations. (=GEOGRAPHIC ISOLATION) - a few individuals move away from the original POPULATION and don’t RETURN. - QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 3. Changes in the GENE POOL the two locations have different environments. The populations slowly “ADAPT” to the environment. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. **Remember QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. that adaptation does not occur because the populations WANT to change. Change occurs because NATURAL VARIATION is present in the population. Some traits will give an individual an ADVANTAGE over others, making them more FIT to the ENVIRONMENT. Greater FITNESS means more OFFSPRING. Those genes will be passed on, while those that are not as FIT to the environment will not be PASSED ON..*** 4. REPRODUCTIVE Isolation The changes in the GENE POOL make it impossible for them to BREED. They might not RECOGNIZE each other any more, or they might have different MATING rituals. Their “REPRODUCTIVE MACHINERY” might not fit together anymore! There could be many reasons why they can no longer produce FERTILE offspring. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. A niche refers to the “PROFESSION” of the species, as well as the RESOURSES the species utilizes for LIVING. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. If, after SPECIATION has occurred, the two populations still fill the same NICHE, they will be in direct COMPETITION with each other for RESOURSES when they try to share the same space. One species may OUTCOMPETE the other and cause its EXTINCTION. However, the competition may cause the species to further ADAPT to fill separate NICHES so that they might live in HARMONY! How do we define a SPECIES? They look different, but they can interbreed, so they are still the same species QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. The Western meadowlark (left) and the Eastern meadowlark (right) appear to be identical, and their ranges overlap, but their distinct songs prevent interbreeding. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. But these two ants ARE the same species - they are sisters, actually! (they have different jobs) Adaptive Radiation (DIVERGENT Evolution) vs. CONVERGENT Evolution ADAPTIVE Radiation – many different species evolve from one COMMON ANCESTOR. (like the SPOKES on a wheel that RADIATE from the centre) ONVERGENT Evolution Many different species will evolve with similar SOLUTIONS to environmental CHALLENGES . . Different sorts of anteaters Though not closely related, they all INDEPENDENTLY evolved the "tools" necessary to subsist on an ant diet: a long, sticky tongue, few teeth, a rugged stomach, and large salivary glands. However, unless the species evolved from a common ANCESTOR, the structures formed are often very DIFFERENT in form. Convergent evolution produces ANALOGOUS structures. Eg. Birds, BATS, squirrels, flying fish and INSECTS all have “WINGS” so that they can FLY, but the INTERNAL structure of the wings is very different. 14.5 – Genetic DRIFT Occasionally, NATURAL SELECTION is not responsible for evolutionary changes. Genetic drift is known as evolution “BY CHANCE.” There are some traits that have evolved despite the fact that they do not give an ADVANTAGE over another. Example: Indian Rhinoceros – ONE horn African Rhinoceros – TWO horns – but there is no ADVANTAGE to having a second horn, or to having only one. In many cases, genetic drift occurs due to a NATURAL DISASTER Example: A FLOOD wipes out the most of the mouse population in that area. By chance, a few of the black mice were AWAY FROM THE AREA. When the water drained away, they were left to REPRODUCE. Now the area has a mostly BLACK mouse population. It wasn’t that the black color was an ADVANTAGEOUS trait; the black mice were just LUCKY! GRADUALISM vs Punctuated EQUILIBRIUM Darwin’s theory of evolution supports a GRADUALISM theory of change. That is, Darwin believed that species change SLOWLY AND STEADILY over a very long period of time, and that they are always changing due to ENVIRONMENTAL PRESSURES. However, the FOSSIL RECORD seems to suggest that there were species that experienced PERIODS of change followed by periods of NO CHANGE AT ALL.. It has been suggested that species experience a type of EQUILIBRIUM with the environment until something in the environment CHANGES. Then the species have to ADAPT, so they undergo RAPID PERIODS of evolution. These periods are followed by equilibrium, and the CYCLE REPEATS. This relatively new and controversial theory is called PUNCTUATED EQUILIBRIUM. # of species # of species Time Time Living Fossils Ex: the horseshoe crab Limulus. This species of crab has not changed in hundreds of millions of years. Could it really have such a great design that it didn’t need to CHANGE?