Introductory biology courses play a pivotal role in shaping students’ exposure to STEMM disciplines and in influencing persistence along life science pathways, yet relatively little is known about who teaches these gateway courses at a national scale. The collective effort to cultivate inclusive experiences for STEMM students relies on the professional and political structures within which instructors of this key course operate in. This study examines the distribution of faculty appointment types in introductory biology across several hundred U.S. colleges and universities sampled to approximate the national landscape by geographic region and institutional type. Using a large, multi-sheet dataset of class sections, we systematically coded instructor titles into contingent (non-tenure-track), ladder (tenure-track/tenured), and other categories and generated both section-level and institution-level estimates of faculty assignment. We then addressed three questions: (a) whether contingent or ladder faculty teach the majority of introductory biology sections nationally; (b) how the distribution of faculty types varies by institutional characteristics; and (c) how estimates of faculty representation differ when each course section versus each institution is weighted equally. Results indicate that, in this sample, ladder faculty teach a majority of introductory biology sections, although there is substantial variability across institutions and clear contrasts by institutional type and context. Comparisons of section-level and institution-level estimates further show that conclusions about “who teaches” introductory biology depend on the analytic lens, with section-weighted analyses emphasizing the typical student experience and institution-weighted analyses emphasizing typical institutional practice. These findings contribute discipline-specific evidence to broader conversations about how the academic workforce is constituted, and by extension creates inclusive environments and provide methodological guidance for studying faculty roles in gateway STEM education.
