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

Abstract

Biological evolution is one of over-arching concepts recommended for student learning by National Science Education Standards (NRC, 1996). 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. 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 (National Academy of Sciences, 1998). Certainly some important aspects of process fit these descriptions: Macroevolution and speciation are unlikely to be demonstrated in a classroom lab experiment. Alberts and Labov (2004) point out, however, evolutionary theory makes no such distinction [between macro- and microevolution]; 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 concepts (for example, National Academy of Sciences, 1998; Desharnais & Bell, 2000). Real-time activities using live organisms are far fewer. Investigating Evolutionary Biology in 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 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 following guideline for this standard: Evolution is consequence of interactions of (1) potential for a species to increase its numbers, (2) genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of resources required for life, and (4) ensuing selection by 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 Principle of Population (1798). In his essay, Malthus wrote that the power of population is indefinitely greater than power in 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 immensity of first power in comparison of second. …