We report our progress in developing a learning progression framework and associated assessments that document pathways to understanding, for middle school (MS) and high school (HS) students, two important aspects of biodiversity: how individuals and populations change over time. Adaptation by selection is limited by the genetic variation in a population. Similarly, an organism’s genes determine the possible range of phenotypes an organism can exhibit through interaction with the environment. Understanding both adaptation and phenotypic plasticity is necessary for predicting the effects of disturbances, including climate change and other human impacts, on ecosystems.
We administered written assessments to 937 middle and high school students in 5 states. We included a diversity of schools: rural and urban, low- and high-performing, and low and high socioeconomic status. In addition to written assessments, we conducted semi-structured interviews to validate written assessments and further explore aspects of student reasoning. We used the analysis of six assessment items and a variety of interviews prompts.
We identified clear patterns in student reasoning about evolutionary changes within a population that extend across selection items, confirming and extending the existing research literature. Students at lower levels of the LP describe all individuals as acquiring a trait in response to an environmental change immediately or over a “long time” with no indication of the importance of inter-generational transfer of genes. Students in the middle describe all or some individuals as acquiring a trait, often in incremental steps, in response to environmental change and emphasize the passing of traits to offspring. Students at the highest level accurately describe adaptation by selection. While patterns in student responses to plasticity items were less clearly defined, many students that correctly understood the mechanism of adaptation by selection (4% MS; 13% HS) did not constrain an organism’s phenotype by genes when asked about a scenario with an individual organism experiencing a phenotypic change (0% MS; 1% HS). We propose that understanding the mechanism of adaptation by selection is not what is limiting students’ understanding of how individuals and populations change, and instead that understanding the nature of phenotypic traits is their largest hurdle. Lower level students described phenotypes as shaped by heredity, response to the environment, and choice “pulling in different directions” while higher level students began to understood that phenotypes are shaped by genes whose expression can be modulated in response to the environment and that genes cannot be changed by the environment.