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Gloria G399 Earth Systems Barbara J. Shaw Understanding Evolution Introduction to evolution To biologists, evolution can refer to either a process or an organizing principle that is a theory. Generally, the word evolution means change and the process of biological evolution is derived from this definition. Biological evolution is a change in the characteristics of a population of organisms that occurs over the course of generations. Some of these changes in populations that are considered evolutionary are inherited via genes. A good example of this process of biological evolution can be the species of organism commonly known as head lice. The word Species means “kind” in Latin and consists of a group of individuals that can regularly breed together, producing fertile offspring, which are generally distinct from other species in appearance or behavior. Back to the head lice species, as some parents of young children have discovered, some populations of head lice in the United States have become resistant to the pesticide permenthrin, found in over the counter delousing shampoos. Initially, lice infections were readily controlled through treatment with these products; however, over time, populations of lice changed to become less susceptible to the effects of these chemicals. However, do not confuse yourself between these genetic change and environmental changes, because there are other changes that may take place in populations as a result of environmental change, which are not considered evolutionary. For instance, the average dress size for women in the United States has increased from 8 to 14 over the past 50 years because of an increase in our average calorie intake and average age, not because of a change in genes. (Colleen Belk, Virginia Borden. Science for life. Page 226) In order to understand Evolution better, we also have to understand some key terms (Theories of evolution) that will be used in this lab. These include; homology and the theory of classification. The concept of homology is the similarity in characteristics among different organisms that has resulted from common ancestry. We will be looking at a good example of this when we examine mammal’s forelimbs. So, even though we may conclude that they have totally different function, we will come to realize that each one of these limbs shares a common set of bones that are in the same relationship to each other even though they may be different in size and relative proportion. Since in this case, homology is in anatomy, that is physical structure, it can also be called comparative anatomy (Page 238). There are two other kinds of homology that are worth mentioning and very important to understanding evolution. These are; Homology in development and homology in biochemistry. Homology in development was observed by Darwin and his contemporaries. This was the resemblance of different chordates (Animal that have a backbone or closely related structure) early in their development. He observed that all chordates produce structures called pharyngeal slits, and most have tails as early embryos. These similarities in early development support the hypothesis that humans, bats, chickens, and snakes derived from an ancestor that developed along a similar pathway and that these species thus share and evolutionary relationship with all other chordates (Page 240). On the other hand, homology in biochemistry comes in the understanding of the nature of biological inheritance. Scientists now understand that differences among individuals arise largely from differences in their genes. These differences are due to randomly occurring mutations that are passed on to descendants. It stands to reason that differences among species must also derive from differences in their genes. So, if the hypothesis of common descent is correct, then species that appear to be closely related must have more similar genes than do species that are more distantly related. The most direct way to measure the overall similarity of two species’ genes is to evaluate similarities in their DNA (Page 240). Lesson plan grade level: Fifth grade Total time for lesson: 30 minutes for set up and observation Setting: Science room or laboratory Subjects covered: Science (Human biology), Anthropology (Onsite data collection) Topics: Various theories of evolution including; common descent, comparative anatomy Goals for the lesson: Students will examine Mammal forelimbs, and look at various characteristics trying to find differences and similarities. They will either be given a handout with various forelimbs pictures on them, or I will borrow some from PSU museum to use. They will try to relate the features they observed to their own body features They will also observe that even though the world in populated by different species; some of them have many similar characteristics. Material need: (For 6 groups of five) www.answers.com 12 papers with homology of mammal forelimbs on them (2 per group; see separate document for 12 tetrapod and 12 mammal handouts) Example: the same skeletal elements are found in the forelimbs of all mammals 12 papers with the theory of classification (Shared characteristics between humans and apes on them; 2 per group; see end of this document for handout) Benchmark 2: Life Science Organisms Group or classify organisms based on a variety of characteristics Describe basic plant and animal structures and their functions Diversity/Interdependence Describe the relationship between characteristics of specific habitats and the organisms that live there Describe how adaptations help a species survive Methods: 1. Each group gets a couple of papers for each theory 2. As a group, students start looking at various characteristics among various mammals 3. At the same time, they note down the similarities and differences they notice 4. They will do this while comparing each animal’s forelimb to the one next to it. 5. Then I will give them background on each one of those animals they will be looking at and their ancestors 6. They will then each try to compare some of the features they find on these animals and what they have. Assessment: They will have one question to answer and will be the following; now that you have done this experiment and have seen these features, what does evolution mean to you personally? This question will be answered both by using their opinions and the experiment they would have conducted. However, each individual’s opinion will come in as a compliment to the experiment even though some people do not believe in evolution. Transformation Evolution happens to populations of living things that reproduce. However it isn't enough to simply reproduce for there to be biological evolution, there must also be some system of genetic inheritance. At least some of the generative information contained in the parent must get passed onto the offspring. Extension This could be extended to many academic areas. One of them is archeology. Evolution is very important in this field in the sense that it requires a study of features and looking back in the past. Being able to go about searching for species of the past in various parts of the globe in order to find a common ground among these species. It can also be incorporated in cultural awareness classes. Especially with people now looking forward to coexist in a planet where no boundaries exist anymore. Understanding the fact that we may be different in one way or another, but we have similarities that may point in the direction of a common ancestor is very crucial and significant for a peaceful existence. Source: (www.voyagethroughtime.org) http://upload.wikimedia.org/wikipedia/commons/9/91/Huxley_-_Mans_Place_in_Nature.jpg