A Lesson on Evolution & Natural Selection

By Curtis, Anthony D. | The American Biology Teacher, February 2010 | Go to article overview

A Lesson on Evolution & Natural Selection


Curtis, Anthony D., The American Biology Teacher


Evolution by means of natural selection is regarded as one of the most significant scientific theories ever elucidated. In his book On the Origin of Species, Charles Darwin (1859) proposed this mechanism to explain how life has changed over geological time and how new species emerge from common ancestors. The following activities model evolution and natural selection using simple materials available to most classrooms.

Scientists routinely use models to simulate or approximate complex systems, evaluate hypotheses, and explore theories. Models are invaluable when controlled experiments cannot be done. For example, mathematical models are used to predict complex global and local weather patterns. Without such models, weather prediction would be less reliable. The model used here is intended to introduce and facilitate understanding of evolution and natural selection.

Extinction is an important component of evolution. Over 99.9% of all species that have existed are now extinct. At times, many species have gone extinct over a very short period; this is called a "mass extinction." There have been at least five mass extinctions, and global climate change has been indicated as a component of each. Because of the continued use of fossil fuels, humans are putting carbon dioxide into the atmosphere at an unprecedented rate. Carbon dioxide is a greenhouse gas, and it traps the sun's energy near the earth's surface. Our world is warming, and global weather patterns are changing in sometimes unpredictable ways. The consensus among the world's scientists is that we are experiencing a sixth mass extinction as a result of global climate change and habitat destruction caused by humans.

** Objectives

* To foster interactive discussion about evolution by natural selection

* To become familiar with terms related to evolution by natural selection

* To model how populations change through time

* To model gradualism and punctuated equilibrium

* To gain perspective on extinction and mass extinctions

* To gain awareness of the current rate of extinction caused by humans

* To develop and improve writing skills through expository writing in science

** Natural Selection

Darwin proposed natural selection as a mechanism of how populations change through time, or evolve. The five principal components of natural selection are as follows:

(1) Organisms produce more offspring than will actually survive to reproduce.

(2) Every organism struggles to survive.

(3) There is variation within species.

(4) Some variations among members of a species allow their bearers to survive and reproduce better than others.

(5) Organisms that survive and reproduce pass their traits to their offspring, and the helpful traits gradually appear in more and more of the population.

** Activity 1: Assemble an Animal

Materials

"Assemble an Animal" handout (see Appendix) One six-sided die

Chalk and chalkboard (or markers and white board)

Instructions to Students

Obtain the "Assemble an Animal" handout and a single die from your instructor. For each of the five categories, roll the die to determine which of the six characteristics will be used in determining your animal's environment. Discuss with your group how you will incorporate adaptations to these characteristics into your animal. You have 5 minutes to discuss, plan, and draw your animal on the board. Please send only one person from your group to draw your animal on the board. Note: The time starts when your instructor gives the signal.

Teacher Notes

The "Assemble an Animal" handout is adapted from Shlomiya Bar-Yam's "Build-a-Beast" evolution Web page at New England Complex Systems Institute (http://necsi.org), which presents a few activities regarding evolution and other topics worth exploring with your students. …

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