Papua New Guineans, who have been genetically isolated for millennia, carry unique genes that helped them fight off infection—and some of those genes come from our extinct human cousins, the Denisovans, a research has found, reports Live Science.

The research also found that highlanders and lowlanders evolved different mutations to help them adapt to their wildly different environments.

"New Guineans are unique as they have been isolated since they settled in New Guinea more than 50,000 years ago," co-senior study author François-Xavier Ricaut, a biological anthropologist at the French National Center for Scientific Research (CNRS), said.

Not only is the predominantly mountainous terrain of the island country particularly challenging, but infectious diseases are also responsible for more than 40% of deaths.

Locals therefore had to find a biological and cultural strategy to adapt, which means that the population of Papua New Guinea is a "fantastic cocktail" to study genetic adaptation, Ricaut said.

Modern humans first arrived in Papua New Guinea from Africa around 50,000 years ago. There, they interbred with Denisovans who'd been living in Asia for tens of thousands of years. As a result of this ancient interbreeding, Papua New Guineans carry up to 5% Denisovan DNA in their genomes.