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Lesson 2.8: How Do Populations Change Over Time?Alternative Ideas |
| Issue | Naive Idea | Scientific Idea |
| Natural Selection (Theory) | Natural selection is a theory, not a fact. | Natural selection is an observable if complex process that can be observed on a daily and yearly basis. |
| Natural Selection (Constant) | Natural selection is a constant. | Natural selection changes with the changing environment and is therefore continuously varying. |
| Natural Selection (Components) | Natural selection is a vague and unitary idea. | Natural selection is a composite which includes, for example, both sexual selection (attractiveness to potential mates) and survivability (including ability to escape predators or pesticide resistance). Various selective pressures may be cumulative or may counter-act one another. |
| Natural Selection (Time) | Natural selection requires a very long time. | Evolution and speciation are cumulative events that occur over relatively long time periods; however, natural selection is a daily event which produces changes from one generation to the next. |
| Acquired Traits | Advantageous traits acquired by parents are transmitted to offspring. | Only traits specified by alleles in the genomes of the parents' sex cells are inherited. |
| Adaptation | Organisms change intentionally (an organism tries, needs, wants to change
its morphology or physiology). |
Living things don't develop adaptive traits in response to needs; however, a change in the environment may select a trait by favoring those individuals who have that trait. |
| Population Changes | Changes in populations occur through a gradual change in a trait of all
members of population. |
Individuals with a given trait (best adapted) generally will contribute more offspring to the next generation, leading to changes in the population composition. |
| Offspring | The number of surviving offspring is similar to the number of offspring produced. | Many organisms produce many more offspring than can survive. |
| Species | All members of a species are essentially identical. |
There is individual variation in some inherited traits in a single species. |
| Competition | Competition occurs usually takes the form of physical combat; the strongest
individuals win. |
Competition occurs among members of a species for space, food, mates, etc., which usually resolves in favor of those best suited to the environment. |
| Randomness of Natural Selection | Natural selection and evolution are random, unpredictable events. |
Natural selection and evolution are not random events, but rather are cumulative processes that result in selective survival and reproduction. |
* A misconception or alternative idea has three primary features: it is a cognitive idea that differs in a significant way from the scientific idea, it is held by a sizable proportion of the population, and it is notably resistant to being taught away; it is often described as a conceptual primitive (Clement, 1982). There are many other types of errors in understanding besides misconceptions (Fisher & Lipson, 1986).
Clement, J. (1982). Students' preconceptions in introductory mechanics. American Journal of Physics, 50 (1), 66 - 71.
Fisher, K. M. & Lipson, J. I. (1986). Twenty questions about student errors. Journal of Research in Science Teaching, 23 (9), 783-803.
