Rare dental trait provides morphological evidence of archaic introgression in Asian fossil record.

Abstract

The recently described Denisovan hemimandible from Xiahe, China [F. Chen et al., (2019) <i>Nature</i> 569, 409-412], possesses an unusual dental feature: a 3-rooted lower second molar. A survey of the clinical and bioarchaeological literature demonstrates that the 3-rooted lower molar is rare (less than 3.5% occurrence) in non-Asian <i>Homo sapiens</i> In contrast, its presence in Asian-derived populations can exceed 40% in China and the New World. It has long been thought that the prevalence of 3-rooted lower molars in Asia is a relatively late acquisition occurring well after the origin and dispersal of <i>H. sapiens</i> However, the presence of a 3-rooted lower second molar in this 160,000-y-old fossil hominin suggests greater antiquity for the trait. Importantly, it also provides morphological evidence of a strong link between archaic and recent Asian <i>H. sapiens</i> populations. This link provides compelling evidence that modern Asian lineages acquired the 3-rooted lower molar via introgression from Denisovans.