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Overview, Life and Natural Selection

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This tutorial is designed to help you understand an important topic in biology. You will read about the topic, view figures, visit related Web sites, complete a case study, and answer interactive multiple-choice questions in the Tutorial Quiz. Take an active part in your learning by writing notes and thinking about the material and answers to the questions. It is best if you have an introductory biology textbook at hand or an online biology resource so that you can look up terms and, if you like, go into more depth on the topic.

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Welcome to Biology 110!

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Welcome to Biology 110: Concepts of Biology and Biodiversity. This course is designed to provide you with an overview of the major themes of biology and to introduce you to the diversity of life on the planet. These web-based tutorials are a major tool to help you learn the material. These tutorials, in conjunction with the Mastering Biology assignments and practice problems on ANGEL will help you learn the course material and increase your learning efficiency. In this first tutorial you will learn how the course tutorials works and you will also get an introduction to natural selection and evolution, major unifying themes in modern biology.

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Features of the Biology 110 Tutorials

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Each tutorial will include an "Introduction, Goals, and Objectives" section . This section provides an overview of the tutorial. You might find it helpful to go back to this section after you complete the tutorial and see if you understand the major goals. A good test for comprehension, upon completing the tutorial, is to pull out a piece of paper and draw out some of the main points of each goal. Remember, the more actively you use these tutorials, the more beneficial they will be to you.

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At the end of the reading, there is a "Terms" list.  The terms list provides a list of biological terms for each tutorial. You should have a working knowledge of these terms. You should not only look up their definitions in your textbook or a reliable source online, but also see how they are used in the tutorials. The terms appear in bold when they are first defined in the tutorial. If you form a study group (and we suggest you do this), then practice using these new words with your partners. Some students find it helpful to use 3x5 cards with the word on the front and the definition on the back to help them learn the more difficult terms. (If you use this method, write the definition in your own words because this will help clarify the meaning of the term.)

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At the end of most tutorials there will be a "Case Study". This case study is an application of the concepts learned in the tutorial to a real-world situation. This will give you an opportunity to apply the basic scientific concepts you have learned to a problem or scenario that is encountered by scientists. There will be questions pertaining to these case studies in class, on ANGEL, and on the exams.  There is no answer key for the case study questions; however, working through the questions asked on ANGEL and in class will help you determine how well you understand the case studies.

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After reading the tutorial and working through the case study, you should return to ANGEL to answer the "Tutorial Quiz" questions. Try to answer the questions without referring back to the tutorial, textbook (if you are using one), or your notes in order to test your understanding of the material. If you answer questions incorrectly - take the time to figure out why. You can send a message to your instructor (all messages sent to instructors should be sent using the ANGEL communicate tab) or meet with an instructor during office hours.

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Introduction, Goals and Objectives

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By the time you finish this tutorial you should be able to:

  • Describe the main features of the tutorials and other online resources used in this course
  • Discuss the complexity of defining "life"
  • Succinctly define "biological evolution" and discuss its role in the diversity of life on earth
  • Succinctly define "natural selection" and explain how natural selection leads to adaptation
  • describe the unique features of the "Evolution Canyons" in Israel and explain how changing landscapes lead to biological evolution
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What is Life?

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Biology is the study of life. But, what is life? We all recognize it, but defining it can be a challenge and there is no single correct definition.  Some features of living things include: order, the need for energy, growth and development, regulation of one’s internal environment, the ability to reproduce, the ability to respond to one’s external environment, and evolutionary adaptation.

We will begin our study of life by examining how life behaves over successive generations. Life is not static, and it changes with time.   The next section discusses how life changes or “evolves” as a result of natural selection.

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Natural Selection and Evolution

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The title of this course is Concepts of Biology and Biodiversity. Evolution (defined most succinctly as changes in the genetic structure of a population) is an important process in biology, and it explains the diversity of life that exists in our world (Figures 1 and 2). We now know that all life is related and can be traced back to a common ancestor that existed some 3.7 billion years ago. In the vast time since life first appeared, evolution has resulted in a continuous branching of new species that can be described as a tree of life. Rooted firmly at the bottom is life's common ancestor, whereas modern species reside at the tree's tips; the vast branching that exists between the two describes the history of life on the planet.

In this class, evolution will be a reoccurring theme. Whenever appropriate, we will discuss how evolutionary processes have shaped life's diversity and adaptations (adaptations are traits that help an organism survive in its current environment). As you will learn, evolution has many facets that have contributed to the diversity of life. However, only one process adapts life to the environment; this process is natural selection.

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An evolutionary timeline of life

 



Figures 1 and 2.  An evolutionary timeline of life
(click images to enlarge)

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What is Natural Selection?

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Natural selection is a process by which a population becomes better adapted to its' environment over time (a more succinct definition of natural selection is “differential reproduction” – the best adapted individuals are more likely to reproduce then less well adapted individuals).  However, environments are always changing and thus the best adaptations in an environment also change.  Changing environments drive evolution via natural selection.

At the most fundamental level, natural selection results in changes in the frequency of certain genes and/or alleles over successive generations within a population. In order for natural selection to act on a population, there must be genetic variation in the population and the genes and alleles that are selected for are the ones that result in adaptation.  As you might gather, genetics and genetic diversity plays an important role in understanding natural selection and we will conclude this course with a study of genetics.

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Summary

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These tutorials,along with the other course materials, are designed to help you focus your efforts in the course and to help you continually assess your understanding of the material. It is important that you make regular progress on the tutorials. Each tutorial will be available in advance of the class meeting, where it will be discussed. We strongly suggest that you work on the appropriate tutorial before each class meeting; the instructor will assume that you are familiar with the material in the tutorial corresponding to that particular day's topic. To gain maximum benefit, we suggest that you work through each tutorial in one sitting. Pick a time (and location) when you can focus without distractions. We suggest that you take notes as you work through the tutorials - if you take an active role in working through these tutorials, you will gain maximum benefit.

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Terms

After reading this tutorial, you should have a working knowledge of the following terms:

  • adaptation
  • biological evolution
  • life
  • natural selection

Case Study for Evolution and Natural Selection

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Evolution Canyons I and II are found in Israel in the Carmel and Galilee mountain ranges (the image above shows Evolution Canyon I (ECI) in Lower Nahal Oren, Mount Carmel, Israel). These areas are ideal for the study of evolution because each range has a north-facing slope with relatively temperate environmental conditions and a south-facing slope with relatively extreme UV radiation (the south-facing slopes receive 200--800% more solar radiation than north-facing slopes), daily temperature variation, and arid conditions.

Scientists are interested in exploring how these different environmental conditions lead to evolutionary changes in organisms. An example of an evolutionary change is a change in coat color in mammals. Many mammals, particularly prey organisms, have evolved coat coloration that matches their environment in order to provide camouflage from predators. Singaravelan et al (2010) investigated how hair melanin content of spiny mice (Acomys cahirinus) has evolved in response to alternative selection pressures inflicted by contrasting colored habitats of Evolution Canyon. There are two main forms of melanin: pheomelanin results in yellow to brown hair color and eumelanin results in gray to black hair color.

  • Based on this information, do you expect mice that live on the “African” slopes to have higher pheomelanin content in their hair or higher eumelanin? What do you expect of mice living on the “European” slopes?
  • Explain how a change in environmental conditions can result in an evolutionary change in a population.

Reference

Singaravelan N, Pavlicek T, Beharav A, Wakamatsu K, Ito S, et al. (2010) Spiny Mice Modulate Eumelanin to Pheomelanin Ratio to Achieve Cryptic Coloration in “Evolution Canyon,” Israel. PLoS ONE 5(1): e8708. doi:10.1371/journal.pone.0008708

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Now that you have read this tutorial and worked through the case study, go to ANGEL and take the tutorial quiz to test your understanding.  Questions?  Either send your instructor a message through ANGEL or attend instructor office hours (the times and places are posted on ANGEL).

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