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Natural Selection and Evidence for Evolution

By 123123m Feb 24, 2013 1426 Words

Natural Selection and Evidence for Evolution:
The mechanism for evolution is called Natural Selection to distinguish it from Artificial Selection. Evolution occurs at the population level because genetics don’t change. The frequencies of different genetic types (genotypes) within a population do change over time & can create new species. There is genetic variation in all populations; some individuals are successful at surviving and finding resources & produce offspring sharing the same genotype as the parent. Enough mutations are selected within the population to create new species. Conditions needed for evolution to occur:

oVariation Within Population; differences in size, shape, physiology and reproductive abilities. Evolution requires variation within the population. oStruggle for Existence (survival of the fittest); Darwin was influenced by Thomas Malthus—High birth rates and shortage of basic needs (food/shelter) forces organisms to compete for survival. The ability to survive in an environment is called fitness. oDescent with Modification (ability of survivors to pass on their traits to the next generation); fitness traits must be heritable, species descended with changes from other species over time, appearing different from ancestors. Natural selection occurs without human intervention, bringing changes in the inherited traits of the population, leading to create new species. Pesticides don’t kill all insects; a few individuals have mutations that give them some resistance to it. When they reproduce they pass on this trait to their offspring. Since all non-resistant insects are killed, this allows the few resistant insects to take over the population---over time all insects in the area become pesticide resistant. Six Evidences of Evolution;

o1. Fossils; (H.M.S. Beagle Voyage) & layers of sediment and volcanic ashes show how species changed over time. o 2. Geographic Distribution of Living Species; organisms face environment selection pressures & develop similar features (not necessarily related). o3. Comparative Anatomy; anatomical structures reveal evolution in 3 ways; homologous, analogous, & vestigial structures. Homologous; Structures have similar anatomy, but differ in function. Shares a common ancestor, & provides evidence of descent with modification. Example; fingers used for grasping. Analogous; Structures with similar functions and appearance, but different anatomy. Not a common ancestor. Example; wings made using different materials and bones (bats vs. birds). Vestigial; Structures with no current functions, but are homologous to functional structures in related organisms. o4. Comparative Embryology; all vertebrate embryos inherit the same basic genetic plan for development from their shared ancestors. o5. Comparative Biochemistry & Genetic Evidence; ability to measure genetic and biochemical similarities; similarities in chromosome structure, sequence of amino acids in proteins & similarity in DNA composition—these all provide evidence of evolution. o6. Artificial Selection; selective breeding (interference of humans). Natural and human activities can change environment causing evolution; black coloration (melanism) of peppered moths caused by industrial pollutants--Pollutants would discolor bark on trees darker moths increased as lighter moths were preyed on. The theory of evolution by natural selection selects organisms best adapted to its environment & better able to survive under those conditions. Darwin used fossils, geographic distribution of living species, artificial selection, comparative anatomy, & comparative embryology to support his theory of evolution. Mostly collected during the H.M.S. Beagle voyage. Wild turkeys can fly. Domesticated turkeys can’t fly—if a population of domesticated turkeys escaped into a new environment where flying isn’t important for survival, they would survive in bushy lowlands/grasslands to hide from predators. Pollution, climate change, & habitat destruction change the environment around the world—faster than species can adapt. Genetically Modified Foods; inserting genes from other species to add desired traits; resistance to herbicides or improved nutritional content. Once genes are inserted they become part of the genome & are passed down. o Advantages of GMF’s:

Pest Resistance; growing GMF’s eliminates use of pesticides & reduce cost of bringing crop to market. Herbicide Tolerance; prevents environmental damage by reducing herbicide usage. Used to kill weeds, but not the GMF. Disease Resistance; GMF’s can be modified to resist viruses, fungi, & bacteria. Cold Tolerance; helps prevent freezing and make crops resistant to cold spells. Scientists use gene from cold-water fish into plants (tobacco/potato). Draught Tolerance/Salinity Tolerance; GMF’s can survive draught or high salt content in soil/groundwater. Ability to grow in inhospitable places. Nutrition; impoverished people rely on a single crop, GMF’s can contain additional vitamins/minerals; nutrient deficiencies can be reduced. Pharmaceuticals; medicines/vaccines are expensive, scientists are working to develop edible vaccines in plants (tomatoes/potatoes). Phytoremediation; Genetically modified plants (poplar tree) clean up heavy metal pollution from contaminated soil.

oDisadvantages of GMF’s
Accidental harm to other organisms; pollen from GM crop is blown by the wind onto other plants on which organisms feed on and perish. Reduced Effectiveness of Pesticides; insects resistant to crops Gene transfer to non-target species; herbicide-tolerant GMF’s accidentally interbreed with wild weeds & transfer the herbicide tolerance genes from the crops into the weeds. Allergenicity; inserting a gene into a plant may create a new allergen or cause an allergic reaction. Cold-water fish genes inserted into tomatoes caused allergic reaction towards tomatoes in people who’re allergic to fish. Unknown effects on human health; scientists are concerned inserting foreign genes into food plants may have an unexpected & negative impact. Economic Concerns; bringing GMF’s to consumers is costly process. Biotech companies profit from this as they invest in GMF creation—the price of seeds can increase so much that small farmers in developing countries can’t afford seeds for GMF crops. Artificial Selection; humans select desired traits that determines an organisms success in reproduction. Ex; breeding heavy chickens so offspring has more weight. Natural Selection; spurred on by environmental changes—organisms best adapted to these changes are better able to survive (survival of the fittest). Example; if temperature gradually decreases, seals would evolve to develop thicker layer of fat to be more resistant to cold temperatures & survive in greater numbers. Artificial selection is still dependent on natural variation in order to select organisms with desired traits.

4) What role does natural variation play in natural selection and evolution? oNatural selection works upon Natural variation.
oNatural variation are random mutations that occur when genes are copied and lead the genomes of the parent to its offspring--genes slightly different from each other instead of exact copies. These give variation naturally. oNatural variation gives different mutations to choose from and natural selection chooses which mutations gets passed down to the next offspring by considering favorable and unfavorable traits according to e.g.: environment -- evolution occurs as organisms now would have more useful features fitting the organisms habitat.

5) Give three lines of evidence that Darwin used to support his theory of evolution by natural selection
1. Fossil Records – ancient organisms have simpler structure than present-day organisms and show gradual change in form. Top layer of fossils represents the closest to present-day organisms & more complexed and recent fossils. This shows descent with modification as the fit individuals passed on their traits to their offspring causing evolution. 2. Common ancestor – Finches from Galapagos Islands showed strong adaptations to their individual isolated habitats, yet are very closely related (different beak shapes) which shows a common ancestor. Adaptation to environment shows struggle for existence.

3. Comparative biochemistry and genetic evidence – DNA composition provide evidence of the descent of related species--the genetic code is the link to ancestral species. As species evolve their genetic codes acquired slightly different genetic codes. Genetic analysis shows humans and apes are closely related with 96% genes in common – the more closely related the more genes in common. 6) In one sentence each, describe the following;

A) One positive effect of direct artificial selection.
Creation of new livestock or crops with desired traits, increasing nutritional content, increasing quality, or resistance to herbicides.
B) One negative effect of direct artificial selection.
Herbicide-tolerant GMF’s will accidentally interbreed with wild weeds and transfer herbicide tolerance genes from crops to weeds.
C) One negative effect of indirect artificial selection.
Indirectly affecting evolution by changing the environment around the world; Pollution, climate change & habitat destruction all change selection pressures on species. 7) Explain how natural selection could produce the modern-long-necked giraffe from short-necked ancestors.

Lamarck proposed the idea on how giraffes couldn’t obtain food (unable to reach higher) which left giraffe’s with longer necks survive and reproduce. While short-necked giraffes died off before being able to reproduce, due to food limitations. Since a longer neck is determined genetically, the longer-surviving giraffes passed this trait more frequently.

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