NEW YORK – With the help of an automatic landmarking method that discerns facial features from two-dimensional (2D) portraits, an international team led by investigators in China and the UK has unearthed dozens of genetic loci linked to facial features, including a chromosome 1 locus originating in Neanderthals that appears to influence nose shape.
The results suggest that modern humans migrating out of Africa to cold, northern regions of Eurasia may have borrowed gene segments from Neanderthals, who were already adapted to that environment, co-senior and co-corresponding author Kaustubh Adhikari, at the Open University and University College London, explained in an email.
As they reported in Communications Biology on Monday, the researchers performed a genome-wide association study focused on facial features in 6,486 array-genotyped individuals from five Latin American countries. Participants had their photos assessed using an automated Face++ cloud service platform to landmark 106 facial features from 2D front-facing photos.
"Given the widespread availability of 2D photographs, the automated landmarking approach we applied here could facilitate a more comprehensive worldwide sampling of human facial variation than hitherto attempted," the authors noted.
The team's search highlighted 42 genetic loci associated with facial features, including the Neanderthal-introgressed chromosome 1q32.3 locus and another 32 loci not associated with facial features in prior studies. Replication analyses in East Asian, European, and African individuals shored up associations at 26 of the new loci in and around genes and regulatory regions related to craniofacial development and neural crest cells influencing cranial features.
Based on the facial measurement data from the GWAS, combined with follow-up mouse experiments to assess new facial associations, the researchers found that the chromosome 1 region originating in Neanderthals coincides with specific nose features, particularly enhanced nasal height.
"The novel region in 1q32.3 shows introgression from Neanderthals, and we find that the introgressed tract increases nasal height (consistent with the differentiation between Neanderthals and modern humans)," the authors reported.
While several past studies have explored the consequences of Neanderthal admixture, highlighting introgressed hominin sequences that have been subject to positive selection in some human populations, the current study is believed to be one of the first to specifically provide a look at the facial effects Neanderthals have had on modern humans.
"It has long been speculated that the shape of our noses is determined by natural selection; as our noses can help us to regulate the temperature and humidity of the air we breathe in, different shaped noses may be better suited to different climates that our ancestors lived in," co-first author Qing Li, a researcher at Fudan University, said in a statement. "The gene we have identified here may have been inherited from Neanderthals to help humans adapt to colder climates as our ancestors moved out of Africa."
In contrast to laborious facial measurements done in past anthropology studies, which were often skewed toward specific traits such as head circumference that were subjective, problematic, and potentially discriminatory, the approach used to identify the new facial feature-related variants was designed to quickly measure a wide range of facial landmarks from a photograph, Adhikari noted.
"[W]e can study all the pairwise distances between all landmarks, thereby removing the subjective choice of what traits to study," he explained. "So this meant we could study a lot of traits in a quick time. Since genomics research is exploding these days with the number of participants reaching millions, such an automated approach would need to be employed to study so many participants."