Viruses have made us who we are

Viruses are not only evil, they once played an important role in human evolution and without them we wouldn’t even exist.

In the Andes Mountains of Colombia, there is a lizard that has a placenta and gives birth to young, unlike other reptiles that lay eggs. BBC.

The virus DNA developed the placenta

Placentas are usually associated with mammals, but the researchers found that lizards developed a placenta using genes from a virus.

The lizards’ ancestors were infected with a virus that incorporated some of their DNA into the lizards’ genomes but did not harm the lizards, and instead the lizards developed a placenta.

Mammalian placenta source

This story is not strange, about a tenth of the human genome comes from viruses and viral DNA has played an important role in our evolution.

Part of the viral DNA is sourced from the mammalian placenta, and other parts are involved in our immune system and the formation of new genes, without viruses we would not have evolved.

bundle of genetic material

Viruses are so simple that many biologists don’t see them as completely alive, a virus is essentially a bundle of genetic material and can only reproduce by infecting living cells.

They mess up the cell’s machinery so that it makes copies of the virus, making their infected hosts sick.

Four retrovisus infect humans

Viruses that insert their genetic material into the host’s genome are called retroviruses, and scientists only understood their nature in the 1960s and 1970s.

Retroviruses belong to a large and diverse group of viruses, but only four are currently known to infect humans, all of which were discovered in the 1980s.

They are the T-lymphotropic virus 1, HTLV-1, which causes a form of cancer, along with the closely related HTLV-2; HIV types 1 and 2 are the causes of AIDS.

DNA is very vital in our genes

If a cell in someone’s skin or lungs gets infected with a retrovirus, it’s bad for that person, but it has limited consequences for the evolution of our species because that DNA isn’t passed on to the next generation.

But if a retrovirus infects germ cells, the viral DNA can be passed on to the next generation. Those pieces of vital DNA are called endogenous viruses or retroviruses and can alter development.

When the first draft of the human genome was published in 2001, it was revealed that about 8 percent of our genome is retroviruses.

All vertebrates have retroviruses

Some are very old, retroviral viruses have been identified on human chromosome 17 that are at least 104 million years old in study year 2013.

This means that a virus infected a mammal during the time when dinosaurs lived on Earth.

Retroviruses are only found in placental mammals, but they are not limited to mammals and reptiles.

“All vertebrates have endogenous retroviruses,” says the molecular virologist. Nicole Grande at the University of Cagliari, Italy, for the BBC.

Not an inactive fossil

Originally, human viruses were seen as inactive fossil remains or “junk DNA,” but human retroviral viruses have been shown to be active, for example, and are important for placenta formation.

Curiously, there is no evidence that retroviruses have entered the human genome in the past 1,000 years. Now extant retroviruses have not been reported to infect germ cells.

For other species it is different, for example, koalas are currently infected with a retrovirus called KoRV and DNA from it is found in some populations of koalas but not in others.

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Read more: Study: Viruses of our ancestors can fight cancer [Dagens PS]