In evolutionary phonetics research, important distinctions between humans and human ancestors are contingent on observations that modern humans possess “roughly 1:1” proportions between horizontal and vertical vocal tract sections. However, few descriptions of diverse adult speaker samples exist. We measured horizontal distance between the anterior-most point of the lower lip and the posterior wall of the pharynx, and vertical distance between staphylion and the superior margin of the posterior lamina of the cricoid cartilage. Our results show that proportions exhibit moderate variation between speakers. We discuss these findings in the context of the purported speech capacities of human ancestors.