This paper examines what counts as a behavioral trait for the purpose of scientific investigation. I develop a cluster of criteria that are neither necessary nor sufficient but provide a reasonable framework for the scientific investigation of behavioral traits. As a result, a basis for normative evaluations emerges that rules some things in (e.g., learning and memory in fruit flies) and other things out (e.g., educational attainment in humans), with attendant consequences for different social and behavioral sciences. 

I develop the concept of methodological shortfall from other existing explanations of science behaving counterintuitively. Methodological shortfall occurs when research communities concentrate their research programs around research questions, but their available methods are constrained in their ability to answer these questions unambiguously. In other words, a research community’s reach exceeds its grasp. I use contemporary behavioral genetics as a case study to demonstrate how the concept of methodological shortfall can help us make sense of ongoing complaints about behavioral genetics research undertaken on humans. Analyzing these issues through the lens of methodological shortfall reveals two paths forward for human behavioral genetics research: (1) continuing to use observational studies like Genome Wide Association Studies (GWAS) and Twin Studies, pursuing incremental improvements such as increased sample sizes, or (2) adopting experimental methodologies that can only be used in model organisms, which means approaching their object of study in an indirect way. After characterizing these two paths, I journey down each one to highlight how that choice impacts epistemic progress. Some researchers in behavioral genetics have chosen to work with model organisms to overcome the methodological barriers inherent in observational studies. I show how their work has generated epistemic progress on central research questions that have not been achieved by those working with human populations. I close with some observations about how the concept of methodological shortfall can contribute to broader discussions within philosophy of science. 

Root formation is a complex developmental process that involves cell elongation, differentiation, lateral root initiation, and responses to environmental factors - all processes dependent on gene products and the proper timing and location of their expression. Previous studies suggest the Arabidopsis thaliana PIRL9 gene could be involved in root development. If PIRL9 is involved in root development, PIRL9 should be expressed in root tissue, and pirl9 mutants should display abnormal phenotypes. To explore PIRL9 gene expression in primary and lateral roots, a reporter gene construct was made by attaching DNA encoding the GUS enzyme to the pirl9 promoter and inserted this construct into the A. thaliana genome.  A. thaliana lines containing this construct were used to examine PIRL9 gene expression in various tissues. In addition, PIRL9 expression was examined along the primary and lateral roots at different developmental stages. In order to elucidate PIRL9 function, primary root length and lateral root number and frequency in pirl9 knockout mutant plants were compared to wild-type controls, as well as in plants defective in a closely related gene, PIRL3. Findings confirm that PIRL9 is expressed in a variety of different developmental contexts, including early embryos at the start of primary root formation, and primary and lateral root tissue. PIRL9 was especially present in primary roots near the formation of lateral roots and lateral root buds. Pirl9 knockout studies revealed the diversity of morphology that A. thaliana primary and lateral roots exhibit under a variety of different environmental conditions.    

Environmental adaptation and species divergence often involve suites of co-evolving traits. Pigmentation in insects presents a variable, adaptive, and well-characterized class of phenotypes for which correlations with multiple other traits have been demonstrated. In Drosophila, the pigmentation genes ebony and tan have pleiotropic effects on flies' response to light, creating the potential for correlated evolution of pigmentation and vision. Here, we investigate differences in light preference within and between two sister species, Drosophila americana and D. novamexicana, which differ in pigmentation in part because of evolution at ebony and tan and occupy environments that differ in many variables including solar radiation. We hypothesized that lighter pigmentation would be correlated with a greater preference for environmental light and tested this hypothesis using a habitat choice experiment. In a first set of experiments, using males of D. novamexicana line N14 and D. americana line A00, the light-bodied D. novamexicana was found slightly but significantly more often than D. americana in the light habitat. A second experiment, which included additional lines and females as well as males, failed to find any significant difference between D. novamexicana-N14 and D. americana-A00. Additionally, the other dark line of D. americana (A04) was found in the light habitat more often than the light-bodied D. novamexicana-N14, in contrast to our predictions. However, the lightest line of D. americana, A01, was found substantially and significantly more often in the light habitat than the two darker lines of D. americana, thus providing partial support for our hypothesis. Finally, across all four lines, females were found more often in the light habitat than their more darkly pigmented male counterparts. Additional replication is needed to corroborate these findings and evaluate conflicting results, with the consistent effect of sex within and between species providing an especially intriguing avenue for further research. 

Cooley, A.M., S. Schmitz, *E. J. Cabrera, *M. Cutter, *M. Sheffield, *I. Gingerich, *G. Thomas, *C. N. M. Lincoln , *V. H. Moore, *A. E. Moore, *S. A. Davidson , *N. Lonberg, *E. B. Fournier, *S. Love, *G. Posch, *M. B. Bihrle, *S. D. Mayer, *K. Om, *L. Wilson, *C. Q. Doe, *C. E. Vincent , *E. R. T. Wong, *I. Wall, *J. Wicks, *S. Roberts (2021). Melanic pigmentation and light preference within and between two Drosophila species. Ecology & Evolution 12 August 2021. doi.org/10.1002/ece3.7998.