Interbreeding with Neanderthals and Denisovans May Have Helped Protect Humans Against Diseases Like Malaria, Study Says

DNA inherited from Neanderthals and Denisovans may have provided humans with protection against infectious diseases, including malaria, a study published in Neuron suggests.

Researchers also found added evidence that these inherited genes could affect biological processes and neurological conditions like autism and attention deficit/hyperactivity disorder (ADD).

For over a decade, scientists have suggested modern humans interbred with other hominin species, including Neanderthals. Evidence of this interbreeding can still be found in the DNA of people living today.

Genomic introgression is where DNA is swapped when two species interbreed. This can result in traits and characteristics being passed from one species to the other.

An example of this is Tibetans' unique aptitude for high altitude living, which is thought to have stemmed from their early ancestors interbreeding with Denisovans—another extinct archaic species from the Homo genus.

Less advantageous traits that we may have inherited from our non-Homo sapien ancestors include depression and social anxiety, as well as an increased susceptibility to inflammatory diseases like type 2 diabetes.

It is thought that Neanderthal ancestry for non-African populations sits somewhere between the 1 and 4 percent mark, though ranges vary. Melanasians and East Asian populations are also thought to carry Denisovan DNA, with up to 5 percent of Melanesian DNA derived from Denisovans by some estimates.

Cave Man
Interbreeding with ancient hominids like Neanderthals and Denisovans may have given modern humans defences against diseases like malaria. MARCO BERTORELLO/AFP/Getty

Typically, scientists have attempted to understand these genomic introgressions by studying the genes themselves, the researchers say. In this research, they focused on the relationships and interactions between genes, which were sourced from the 1000 Genomes Project—a catalogue of human genomes—and 35 Melanesian individuals.

"Our results suggest that gene interactions and associations between different archaic mutations have played an important role in human evolution," Alexandre Gouy, one of the study authors, from the University of Bern, Switzerland, told Newsweek.

Some of the inherited genes analyzed in the study have been linked to autism and ADD. Others are thought to influence biological processes, such as energy metabolism. But some of the most intriguing mutations looked at were those related to protections against infectious diseases—and malaria in particular, said Gouy.

"When looking at immunity genes ... it was interesting to see that they were involved in the response to all kinds of pathogens: virus, bacteria and protozoans—such as the malaria parasite," he said.

This suggests DNA inherited from extinct hominids bolstered the human immunity to infectious diseases, adding to existing research that suggests interbreeding with Neanderthals improved humans resistance to infections and susceptibility to allergies.

One of the "most striking" findings was evidence of an adaption in the genes of Papua New Guineans inherited from ancient hominids, which may provide some kind of protection against malaria.

However, the researchers are keen to stress their findings are preliminary. While it is becoming increasingly evident that humans have adopted genes from ancient hominids, it is unclear how this affects people in the 21st century.

"It remains very difficult to quantify precisely the effect of those mutations," Gouy said. "Health and behaviour result from the interaction of a complex genetic background and the environment. Hence, the impact of genetics on the immune system and behaviour is difficult to assess."

Tibetan Nomads
Tibetan nomads riding across Shey La pas in the Nepal Himalaya on September 5, 2011 in Dolpo, Nepal. Tibetans ability to live high in the mountains is thought to derive from Denisovan DNA. Zzvet/iStock