Archaic Hominin Introgression in Africa Contributes to Functional Salivary MUC7 Genetic Variation | Molecular Biology and Evolution | Oxford Academic
https://academic.oup.com/mbe/article/34/10/2704/3988100Humans Had Sex With Ancient 'Ghost' Species, Spit Analysis Shows | Inverse
https://www.inverse.com/article/34635-ancient-humans-ghost-species-spit-analysis