Recent research from the University of Colorado Boulder has investigated a gene passed from Denisovan populations to modern humans, which underwent positive selection in Indigenous American populations. This finding presents a unique perspective on modern human genetic admixture with early human populations, highlighting how modern human populations could have benefited from contact with other hominins.

The MUC19 gene encodes mucus production. Mucus is commonly found in the nose and trachea and helps prevent infection.

Therefore, increased mucus production could have been a survival advantage, especially in ancient environments where infection posed a large health risk.

Researchers compared MUC19 groups in ancient modern humans and Denisovans.

They pointed out similarities between the genomes of ancient Indigenous American populations and the Denisovans, and found that Neanderthals had the MUC19 variant.

The gene’s presence in both modern human and Neanderthal genomes suggests a unique method of gene transmission.

Previous gene analysis has noted the Denisovan genetic mixture with Neanderthals. The ancient human populations study demonstrated an unusually large presence of Neanderthal genetic material, which contained the Denisovan MUC19 gene. This suggests that human populations inherited this gene from Neanderthals, who inherited it from Denisovans.

The findings help counteract the simple assumption that genetic flow from early hominins to modern humans was one-way.

Instead, the various hominin species passed genetic material between each other, leaving a complex legacy on our modern genomes. Further, the location-specific presence of the gene and its comparative rarity in non-Indigenous American human populations suggest that such genetic material could have imbued specific survival advantages in early modern humans and helped them survive challenging environments.

There are limitations with these findings.

However, Denisovan genomes are extremely rare, with only five genomes known to date, all originating from Denisova Cave in modern-day Russia.

Furthermore, the MUC19 gene remains understudied.

More research is needed to uncover what survival advantage the gene conferred on Indigenous American populations.

Single Variable Tandem Repeats are a section of repetitive nucleotides like those found in the MUC19 gene.

They are long and difficult to sequence, meaning new technologies are needed to further investigate these genes and uncover their evolutionary history.