Molar crenulation trait definition and variation in modern human populations.

Crenulated molars have been used extensively in biological anthropology. However, the trait has not been formally defined, nor have population frequencies been thoroughly outlined. This study provides a formal definition of molar crenulations and data on their presence in a large sample. Data were collected on maxillary and mandibular molars of modern dental material from various populations: South African, Hispanic, Japanese, American White, and American Black (n = 750). Molar crenulations were defined and a rank-scale created. Statistical analyses include chi-squared, correspondence analysis, and trait correlations. Significant statistical differences were found between populations in all molars. Minimal sexual dimorphism was noted, and is most pronounced among the American Black sample. Generally, American White and Japanese samples showed lower frequencies of molar crenulations, the highest frequencies were seen in the American Black and South African samples, and the Hispanic sample was intermediate. Correspondence analysis showed that American Black samples tended towards grade 2, and South African samples were more often a grade 1. American White and Japanese samples were most often grade 0, and Hispanic samples were intermediate. Correlations were noted across the molars. Population differences exist in the presence of molar crenulations, which were likely shaped by evolution. Based on these results molar crenulations can be added to the suite of traits currently used to study population differences.