Academic journal article The American Biology Teacher

Malthus under a Microscope: Using the Soil Nematode Caenorhabditis Elegans to Test Darwin's Premises about Populations

Academic journal article The American Biology Teacher

Malthus under a Microscope: Using the Soil Nematode Caenorhabditis Elegans to Test Darwin's Premises about Populations

Article excerpt

Biological evolution is one of the over-arching concepts recommended for student learning by the National Science Education Standards (NRC, 1996). As with all such complex concepts, student understanding of evolution is improved when instruction includes hands-on, inquiry-based activities (Layman, 1996). However, even authors writing in strong support of teaching evolution sometimes offer discouraging remarks about using inquiry-based learning. "In spite of strong justification for including evolution-related instruction in biology curricula, 'descent with modification' is a particularly difficult educational issue, for by its very nature, evolution is an abstract and generally nonobservable phenomenon" (McComas, 1994, p.5). "Things in science can be studied even if they cannot be directly observed or experimented on" (National Academy of Sciences, 1998).

Certainly some important aspects of the evolutionary process fit these descriptions: Macroevolution and speciation are unlikely to be demonstrated in a classroom lab experiment. As Alberts and Labov (2004) point out, however, "evolutionary theory makes no such distinction [between macro- and microevolution]; the processes that lead to changes within species, when accumulated over time, also can give rise to new species." That those processes--such as genetic variability, and differential survival and reproduction within a population--can sometimes be observed directly in living populations is vividly described in Weiner (1994).

A number of paper-and-pencil and simulation activities have been developed to give students hands-on experiences with evolutionary concepts (for example, National Academy of Sciences, 1998; Desharnais & Bell, 2000). "Real-time" activities using live organisms are far fewer. Investigating Evolutionary Biology in the Laboratory (National Association of Biology Teachers, 1994) includes six activities using living organisms (along with 17 simulation or paper-and-pencil activities and two activities using fossils or preserved specimens). National Association of Biology Teachers (1994) and National Academy of Sciences (1998) offer activities or suggestions for using fruit flies, "red wiggler" worms, bacteria, fungi, plant proteins, and dihybrid crosses of plants.

The goal of this laboratory activity is to provide students with an instructive and classroom-friendly living model with which to test, firsthand, some of Darwin's premises (influenced by his reading of Thomas Malthus) about populations, competition, and natural selection. This activity addresses the following National Science Education Standards for grades 9-12:

* Content Standard A: "As a result of their activities in grades 9-12, students should develop abilities necessary to do scientific enquiry."

* Content Standard C: "As a result of their activities in grades 9-12, students should develop an understanding of ... biological evolution." In particular, this activity speaks to the following guideline for this standard: "Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring." (National Research Council, 1996).

For both Charles Darwin and Alfred Russel Wallace, a key insight leading to their theory of evolution by natural selection was Thomas Robert Malthus' Essay on the Principle of Population (1798). In his essay, Malthus wrote that "the power of population is indefinitely greater than the power in the earth to produce subsistence for man ... Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison of the second. …

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