The researchers examined the genomes of a total of 67 people with cancer, and found they contained six of the sequences unique to ancient humans. This means that the viruses probably infected our ancestors before we split from the lineage that led to Neanderthals and Denisovans roughly 400,000 years ago. The study was published in the journal Current Biology.
Endogenous retroviruses (ERVs)—which are DNA sequences left by viruses which pass from generation to generation—are supposed to comprise about 8 per cent of human DNA. This 8 per cent is supposed to form at least 90 per cent of all ‘junk’ DNA in the human genome. This DNA is so called because it has no known function and seems useless. However, the researchers caution that it may not entirely be useless. Two so-called junk viruses, under certain circumstances, may be combining with each other to cause diseases like cancer. This may be the case, since past research has shown how cancer is caused among mice with poor immune systems when ERVs are activated by bacteria.
The researchers now plan to study and look for direct links between these ancient viruses, which are hardwired into human DNA, and modern diseases such as AIDS and cancer. They will soon be using modern DNA sequencing of 300 cancer patients to see how widespread these viruses are in the modern population.