Biology Homework Chapter 13: Evolution - Natural Selection
Textbook assignment: Chapter 13: How Populations Evolove, sections 1-10.
- 13.1 The text presents evolution as the central theory of biology, the thread that ties all the other pieces together. Keep this in mind as we study this unit and the next, both of which address the similarities between organisms (based on the common chemical processes and cell functions we have been studying) and the differences that exist between species and between individuals. Be able to identify the theories put forward by Darwin's predecessors:
Anaximander: simple precedes complex
Aristotle, the Judeo-Christian creation story: all species were created at one time and are fixed (no new species, no changes)
Buffon: studied fossils, thought catastrophes caused species to become extinct
Lamarck: thought species "learned" new characteristics
Lyell: geological change is gradual and occurs at a constant rate
Biology and geology are now interdependent studies when it comes to accounting for fossil evidence of previous species and past geological ages.
- 13.2-3 Darwin proposed natural selection as a mechanism to explain changes in the distribution of characteristics in individuals of a species over time. In this part of his theory, no new species are created, but the frequency of a given trait in a population shifts over time as those members of a species who lack the form of critical traits that allow them to survive fail to reproduce.
- 13.4 Fossil evidence is used to try to establish a sequence of development based on geological interpretation of the age of the rocks containing the fossils. Dating is done by comparing levels of radioactive isotopes (we have to make assumptions about the starting concentrations of the isotopes), and by looking at stratification levels.
- 13.5-6 Geographic distribution of species, common structures (homologous structures), similar modes of development in individuals, and common traits (such as similar DNA sequences) are used to supplement fossils as evidence for evolution. Remember that for serious consideration by the scientific community, any alternate theory must address and account for these observations as successfully as the current dominant theory, without recourse to non-scientific evidence.
- 13.7 Evolution is not used to explain changes in an individual, but in traits expressed in populations. The only traits that can be considered must be inheritable traits. Over time, the fraction of a population's individuals carrying a particular trait (allele for a given gene) will change in response to environmental factors.
- 13.8 The only factors that can introduce new traits are mutations in the nucleotide sequences of DNA. "Learned traits" cannot be passed on through any material means. New combinations of traits occur naturally when sexual reproduction includes the mechanism of "crossing-over" during meiosis.
- 13.9-10 The Hardy-Weinberg equation predicts the percentage of a population with a given trait if NO environmental factors influence it. Changes in the population indicate the level of environmental factors acting on the population. Equilibrium requires calculation of the Hardy-Weinberg equation in large populations with no mutation, random mating, and on external influences.
Read the following weblecture before chat: The theory of evolution
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Check out the Evolution in Action game at the PBS Nova site. Click on Launch interacive. Read the Rules and Instructions (available from buttons in the lower right of the game screen).
How does changing the environment (changing the background colors) change the population?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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