They don't consider participation or hours spent studying as explanations for bimodality. This makes their method of determining belief in the "geek gene" quest

They don't consider participation or hours spent studying as explanations for bimodality. This makes their method of determining belief in the "geek gene" questionable, and could invert the moral story of their results: Perhaps lecturers seeing low lecture attendance would like to believe their grade distributions are bimodal, but the data shows the lecturers' impact is at best a tiny factor among many, and grades are determined by factors out of the lecturers' control, such as students' ability.