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Natural Selection Review Sheet Courtesy of: Pamela J. Shlachtman, Miami Palmetto High School The Theory Darwin, after visiting the Galapagos Islands and seeing finches with obvious similar origins doing different things according to the niches they had taken, came up with his Origin of the Species. A lot of his work was ridiculed because people immediately jumped on the monkey - man thing and the "survival of the fittest" idea. There are things that one needs to know about Darwin's theory before any ideas are worked with. One thing is that all the things you see today are a result of selection and do NOT come from one another. Today's chimpanzee is a result of millions of years of selection and has nothing to do with today's Homo sapiens. Both chimpanzee and man have evolved along separate routes to look like what they are today. Another thing is that survival of the fittest does not necessarily mean the strongest. The fittest refers to the ability to reproduce. Those organisms that have 100 % or their young reproduce are the fittest. If strength were a factor, Tyrannosaurus rex would still be around. Darwin did not have the benefit of DNA. He had no idea how traits were passed on and this was one of his problems in his theory. Not having the DNA concept made his work even more phenomenal. What is the Darwinian theory of the Origin of the Species that has caused so much debate in the world? We still have debate over his theory. Some people still believe that man and all other creatures were created in 4 days in the year 4004 BC. Some people believe that a supreme being created everything in 4 days. Of course there is an argument on how long those for days actually were. Were they 24 hours or 4 million years or 400 million years? Does the Supreme Being decide what organism makes it and what doesn't? Very speculative. You may believe what you wish to believe. However, this presentation is the most updated theory of evolution and selection that I could find. Darwin's Theory of Evolution All organisms have the ability to produce more individuals than can survive. A female cod lays millions of eggs. If all of them survived, the oceans would be crawling with cod. Most of them never survive. The environment has things that kill organisms. Too hot, too cold, too dry, storms, floods, predators all contribute to the death of organisms. Too frequently, there is not enough food in the ecosystem to sustain the life there or the predators are too many or too good. Competition occurs for the food and space in the ecosystem. Not many organisms are exactly like. Individuals vary , some drastically. They may differ in color, in size, in speed, in resistance to disease and other traits. Some of these traits are inherited. Some of the inherited traits allow the organisms to survive better than others in bad times. Those that have those traits survive. Those that don't. don't'. This is called adaptation. Some mutations are harmful but many are harmless. Some are advantageous which result in genetic traits that give that organism better chance of reproduction. Some of the adaptive traits are protective coatings, gripping mechanisms , and the ability to hibernate in unfavorable conditions. Those with favorable traits soon mesh with other favorable traits and the mutant young are much better off. When the trait is predominant in the population, natural selection has occurred. Because those that have more advantageous traits have more offspring, each generation contains more of those individuals. The number of organisms without the advantageous traits decreases. This is called evolution. It isn't a difficult theory but it has implications that are not liked by religious groups and some non-religious groups. However, today, it is fairly obvious and is VERY difficult to refute with the fossils that we find. Man's fossils are very different than man today. His weight, height and brain capacity has changed dramatically since written history has started. The average Egyptian male was 5 ft tall. The average Roman soldier was 5' 4". The average American soldier is 6'. The average Watusi is 6'6". A person 7 ft tall was unheard of 100 years ago. Today , there are a lot of them, especially in the NBA. Obviously, height is an advantage. There is NO doubt that tall women are MUCH more successful in business than short women. Tall men have a better chance of employment than short men. The average primitive man was less than 4 ft. Natural Selection The entire genes of all the organisms in the population are called the gene pool. Any change in the gene frequencies in a population is called genetic drift. Many are independent variables. A massive kill-off of a population, such as a disease or weather that allows the individuals to survive will randomly change the gene pool. Some are density dependent. In large gene pools, the favored traits tend to hide or eliminate unfavorable ones until they never appear again. Giraffes are a good example. There used to be tall giraffes and short giraffes, both few from the top and edge of trees in a savanna. During hard times, the short ones could feed only from the sides. The short gene was a definite disadvantage and the short gene disappeared from the gene pool. There are 3 types of selection: Stabilizing selection - The population eliminates the "edges" of the population, the not so normal individual. Disruptive selection - The common traits disappear leaving the edges of the population. This is very common on islands. Many finches living on an island with many niches are in danger of a disease that would wipe out many flowering plants. If a change in the flowers occurred, only the finches with longer beaks could feed. Seeds of plants that are very small and thin to the extreme of being very large and thick that only a large bird could break, the large bird would ignore the small seeds. The bigger than average bird may do away with the center section of the seeds leaving only the large and small ones. This is disruptive. Directional selection - One end of the tolerance chart starts to disappear. The pepper moth of England is a perfect example. Limits to Adaptation A change in the environmental conditions can lead to a change in the genes only if that gene was there in the first place Adaptation of that gene is limited by the population's reproductive power. R-strategist populations will adapt quickly but K strategists can take millions of years. Even though a favorable gene is in the populations, it may take a lot of the population to die to allow the favorable gene to advance Coevolution - two species that have interactions cause changes within their respective species. The Arctic fox and Arctic hare both have white coats in the winter and brown in the spring. Theories of Beginnings If natural selection results in gradual incremental changes in the genetic composition of populations, why isn't there one continuous spectrum of organisms all the way back to the origin of life? We believe there is but there are a lot of organisms (parts) missing simply because they no longer exist. We know that saber toothed tigers existed but they no longer do. Why not? Where did their niche go? Why couldn't they make it and the lynx did? How did one organism show up and the other disappear? First, look at the idea of a species. A species is a reproductively isolated individual. Lions and tigers can breed with one another to produce a tiger or a lion but they don't. Why not? Because there is a serious desert and several mountain ranges between the groups. They are reproductively isolated. What would happen if a species were to be split by a river shift and they could not swim. Suppose the system on one side of the river all of a sudden became very different. The individuals in the population of the East Side may have a trait that allows them to survive on the East Side. This trait would be passed on and the number of individuals in that area would increase drastically. All of a sudden, the river shifts again and the two types are mixed again. They may or may not be able to reproduce with one another. This is called speciation and one species is, presto, two. How did the Earth generate and how did life actually appear. It is thought that the Earth with all the components of our universe were created at one time, the Big Bang Theory about 6 billion years ago. This is a result of finding nothing from outer space over 6 billion years old. The Earth would have condensed about 5 billion years ago. It would have been too hot to have water but gradually developed it. The atmosphere was methane and nitrogen. If you were to stand on the spot where you are now, if there would have been land there (and there wasn't) 4 billion years ago, you would die of asphyxiation in about 4 minutes. It is thought that about 4 billion years ago , the oceans had about 1 % organic matter and the amino acids and polypeptides formed the first life. The first life is referred to as phototrophs and they produced oxygen. In the Cambrian period, the atmospheric level of oxygen was probably 1 %. By the end of the Silurian period, about 400 million years ago, it had reached about 2 %. Huge numbers of phototrophs dumped massive amounts of oxygen into the atmosphere that set the stage for animals. Oxygen was converted to ozone and the ultra violet light, deadly to animals was reduced. 2-300 million years ago, in the late Silurian period, massive amounts of plants occurred and the plant niches abounded. The Permian period provided foods for the reptiles and the huge reptiles that followed but the end of the Mesozoic era found most of the huge plant growth gone and the large reptiles gone. Mammals began to dominate the scene and we have modern changes to look at. What happened to the animals that are not there.? Extinction.99% of all species are extinct. Extinction Extinction means the disappearance of a species form the face of the earth. If extinction is bad, then things have been bad for millions of years as practically all the species that have ever been alive are now extinct. The background rate for marine organisms is abut 3-5 families or 180 -300 species per million years. Most of the losses have been due to predation, competition, habitat change, and reproductive rates. There have been periods of abrupt changes which may or may not have been the result of cataclysmic events such as the collision of earth with an asteroid. Fossil records indicate at least 6 periods of mass disruption on land and 4 in the oceans. During the last disruption, 20 families and up to 1200 species disappeared in the oceans. Most mass disruptions have occurred in the late Ordovician, Permian, Triassic and Cretaceous Periods. It seems to average about every 26 million years and coincided with meteor showers. The biggest disruption was 65 million years age during the Cretaceous Period. A very high amount of phytoplankton disappeared, drastically reducing the oxygen and the rest of the dinosaurs. Because of the high amount of iridium deposited in layers of that period, and the fact that iridium is rare on Earth but VERY abundant in asteroids, it is thought that a large asteroid collided with the earth causing a decline in the solar radiation reaching the earth, depletion of the ozone and otherwise messed the earth up for thousands of years. Extinction is a natural process in evolution of the species. Man has interfered with the extinction process. Instead of killing off 1 per hundred years, we are killing off many per hundred years. We are killing off a lot of animals. The latest biggie kill was the Dusky Seaside Sparrow that lived in Cape Canaveral. Because the mosquitoes were so numerous in this salt water marsh, NASA sprayed the marsh continually. It killed the mosquitoes, the birds, the fish and all the rest of the life in the marsh. Along with the pressure of housing, NASA draining and cement, the removal of its habitat and foods, the Dusky died out a few years ago. Knowing that we could not possibly kill off the passenger pigeon because the flocks darkened the sky, we shot and trapped millions of them. One hunter alone trapped over 10,000. They died off rather rapidly. The Dodo, the Stellar's Sea Cow, hundreds of Tropical Rainforest Animals, small fishes of rivers and streams that could not take reservoirs, simply too many to list have disappeared. Some are just about gone. The Hawaiian Monk Seal is dying out at about 100 per year. There are currently 550 left. The Guadeloupe Seal is disappearing as rapidly - less than 300 left. The California Condor stays alive only because man keeps them alive. The Whooping Crane is coming back but could not make it if man didn't help it. Zoos, parks and preserves are the only place species diversity is going to find refuge. Wildernesses, constantly under attack in every government, are not going to withstand the pressure of hunger and greed. Loggers and miners look at a wilderness and find a "waste of land and resources" whereas environmentalists look at a wilderness as the last possible species diversity areas in the world. The environmentalists are not winning. It is only a matter of time until the extinction level is massive again, not because of a catastrophe but because of people. Natural Selection/Planned Natural selection has found a place in the breeders of the world. New species have been made all over the world to provide new foods and new species to look at. New orchids, new lilies, new miracle grains and all found in our society. Our new wheat is now planted all over the world. It is a result of the new hybrids crossed with the original Jerico wheat to produce a wheat rust resistant wheat. It produces far more wheat per acre than the old wheat. The miracle rice produces 4-5 times the amount of rice on the same acres. The new hybrid corn produces 100 bushels per acre compared to the 40 in the 1950s. We are breeding new animals. We are beginning to engineer changes in DNA which will drastically affect selection. Our breeding has developed cattle that are so fat they could not survive the natural range. Horses that could not tolerate the natural world, hairless dogs that would die out immediately in China where they originated and so on. We are "selecting" what we want, not what is naturally selected. It may be good, it may be a disaster. Who knows? Will genetically engineered people be the next step in our evolution? Will the world outside go away leaving only the methane breathers of the vents alive to start a new evolutionary process. Only time will tell but we are doing what we can to destroy the species of Homo sapiens and there is only one species left. Human's Effect on Natural Selection We simplify ecosystems. We eliminate some wildlife by plowing clearing forests, filling in wetlands and use one crop, monoculture. This eliminates many species in the system. We spend fortunes trying to keep that monoculture alive We strengthen some populations of pests and bacteria by treating them with pesticides and antibiotics making them resistant and thereby stronger than their competitors. We eliminate some predators. We eliminate prairie dogs, wolves, coyotes, lions, tigers, eagles, etc because they prey upon tamed species. We introduce competition or predators into ecosystems Dutch Elm Disease, Lampreys into the Great Lakes, carp, walking catfish, Melaleuca. We over harvest species. Cod, Anchovies, Salmon, overgrazing 6. Interfering with the normal chemical cycling and energy flows monoculture reduces nitrogen cycling, CFC's, PCBs, heavy metals additional CO2 , rapid transmission of sulfur and carbon into the system.