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In this reading-, writing-, and discussion-based activity, students explore bacterial evolution occurring in a stable environment, which counters the intuitive misconception that environmental change is a necessary component to natural selection. A landmark study provides the backdrop against which students can challenge their thinking about what it means for a population to evolve.
two to three 50-minute class periods
This lesson is meant to be used early in the evolution unit.
Correspondence to the Next Generation Science Standards is indicated in parentheses after each relevant concept. See our conceptual framework for details.
- Evolution results from selection acting upon genetic variation within a population. (LS4.B)
- Traits that confer an advantage may persist in the population and are called adaptations. (LS4.B, LS4.C)
- Inherited characteristics affect the likelihood of an organism's survival and reproduction. (LS4.B, LS4.C)
- Depending on environmental conditions, inherited characteristics may be advantageous, neutral, or detrimental.
- Natural selection acts on the variation that exists in a population. (LS4.B, LS4.C)
- Over time, the proportion of individuals with advantageous characteristics may increase (and the proportion with disadvantageous characteristics may decrease) due to their likelihood of surviving and reproducing. (LS4.B, LS4.C)
- Scientists use experimental evidence to study evolutionary processes.
- There is variation within a population. (LS3.B)
- The number of offspring that survive to reproduce successfully is limited by environmental factors. (LS4.B, LS4.C)
- Natural selection is dependent on environmental conditions.
- Environmental changes may provide opportunities that can influence natural selection. (LS4.B, LS4.C)
- Fitness is reproductive success - the number of viable offspring produced by an individual in comparison to other individuals in a population/species.
- Evolution occurs through multiple mechanisms.