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The human genome contains billions of pieces of information and around 22,000 genes, but not all of it is, strictly speaking, human. Eight percent of our DNA consists of remnants of ancient viruses, and another 40 percent is made up of repetitive strings of genetic letters that is also thought to have a viral origin. Those extensive viral regions are much more than evolutionary relics: They may be deeply involved with a wide range of diseases including multiple sclerosis, hemophilia, and amyotrophic lateral sclerosis (ALS), along with certain types of dementia and cancer.

For many years, biologists had little understanding of how that connection worked—so little that they came to refer to the viral part of our DNA as dark matter within the genome. “They just meant they didn’t know what it was or what it did,” explains Molly Gale Hammell, an associate professor at Cold Spring Harbor Laboratory. It became evident that the virus-related sections of the genetic code do not participate in the normal construction and regulation of the body. But in that case, how do they contribute to disease?

An early clue came from the pioneering geneticist Barbara McClintock, who spent much of her career at CSHL. In the 1940s, long before the decoding of the human genome, she realized that some stretches of our DNA behave like infectious invaders. These DNA chunks can move around through the genome, copying and pasting themselves wherever they see fit, which inspired McClintock to call them “jumping genes.” Her once-controversial idea earned her a Nobel Prize in 1983.

Geneticists have since determined that jumping genes originate in the viral portion of the genome. Many of these genes turn out to be benign or even helpful. “But some of the things are full-on parasites,” Hammell says, like infections embedded within our own DNA. All it takes to set these bad actors loose, she is finding, is a slip-up in the body’s mechanisms that normally prevent the genes from jumping around and causing harm…

Half of your genome started out as an infection; if left unchecked, some parts of it can turn deadly all over again: “The Non-Human Living Inside of You.”

See also: “The Wisdom of Pandemics– viruses are active agents, existing within rich lifeworlds. A safe future depends on understanding this evolutionary story.”

* “‘Life’ is of course a misnomer, since viruses, lacking the ability to eat or respire, are officially dead, which is in itself intriguing, showing as it does that the habit of predation can be taken up by clusters of molecules that are in no way alive.” – Barbara Ehrenreich, Living with a Wild God: A Nonbeliever’s Search for the Truth about Everything

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As we check our baggage, we might send reforming birthday greetings to Abraham Flexner; he was born on this date in 1866.  The founding director of Princeton’s Institute for Advanced Studies, Flexner is best remembered for his pioneering work as a reformer of American higher education, especially medical education.  On the heels of his 1908 study, The American College, in which he effectively critiqued the university lecture as a method of instruction, he published the Flexner Report, which examined the state of American medical education and led to far-reaching reform in the training of doctors.  The report called on American medical schools to enact higher admission and graduation standards, and to adhere strictly to the protocols of mainstream science in their teaching and research.  While one unintended consequence of Flexner’s impactful advocacy was the reversion of American universities to male-only admittance programs to accommodate a smaller admission pool (female admissions picked up again only later the century), most historians agree with his biographer, Thomas Bonner, that Flexner was “the severest critic and the best friend American medicine ever had.”

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