Viruses were discovered in 1892, and yet even in 2018, researchers are still uncovering new secrets about these infectious invaders. Viruses are not quite living things and have no way to reproduce on their own. Instead, they’re made of genetic material, usually DNAor its chemical cousin RNA, that’s wrapped in a protein coating.Because of their ability to integrate their genetic code into the code of their host, viral genes are found hidden in the genes of many living things, including humans. But exactly how and why viruses work their genetic tricks remains a mystery that researchers working in a wide range of fields, from evolutionary biology and molecular biology to neurology and the study of chronic diseases, are trying to solve.

An ancient virus in the human brain

The neurons of animal brains, including human brains, hold the genetic remnants of an ancient viral infection that may be key to how thought processes work, researchers reported in two papers in the journal Cell in January. The researchers discovered that a gene called Arc, which is found in four-limbed animals, is a genetic code leftover from an ancient virus. Moreover, they found that this gene is crucial to nerve cells’ ability to build certain types of tiny packages of genetic material and send them off to other nerve cells. This process explains how nerve cells exchange the information that is needed for reorganization of cells.

Brain functions including conscious thought and the concept of the “self” may only be possible because of this process, the researchers said. And if the process does not work properly, the synapses, or the junctions between the neurons, may become dysfunctional. More research is needed to understand how the Arc gene became a part of the animal genome, and exactly what information is passed from one neuron to another because of instructions from Arc, they said.

Viruses are literally falling from the sky

A long-standing mystery about viruses finally got an answer in 2018: The reason why viruses that are genetically similar to each other can be found great distances apart on Earth is that viruses travel through the atmosphere on air currents. In a paper published in January in the Multidisciplinary Journal of Microbial Ecology, researchers reported that viruses can hitch rides on particles of soil or water and swing high into a layer of the atmosphere called the free troposphere, and then eventually plop down in a completely new spot.

The researchers also found that when viruses reach the level of the free troposphere, which is found approximately 8,200 to 9,800 feet above Earth’s surface, they can travel much farther than would be possible at lower altitudes. It turns out that the free troposphere is teeming with viruses, and due to the action of the air currents within it, a given square meter of Earth’s surface may be showered with hundreds of millions of viruses in a day, the researchers said.