By Brian W. Donnelly, M.D., I.B.C.L.C., Pediatric Alliance — North Hills Division



One of the more interesting results coming out of the Human Genome Project was that the average human genome contains a certain percentage of viral DNA. The most recent estimate is that 8% of our DNA is viral.

It appears that that one of our ancient ancestors was able to survive a viral infection and somehow commandeered its genetic material.  Sarah Zhang points to research suggesting that the placenta may have used this genetic material to the advantage of our species:

Most viral infections are as fleeting as a cold, but two things made the ancient ones unusual: One, these viruses had the special ability to copy themselves into the DNA of their hosts. And two, they sometimes got lucky enough to copy themselves into an egg that became fertilized and grew into a full-fledged adult. So that viral DNA got passed down from generation to human generation as so-called endogenous retroviruses.

But there’s no need for alarm about the DNA of viral origin teeming inside your cells. Some of it may even make you you. As a growing fetus, you co-opted a gene from an ancient virus to form the placenta that kept you nourished in the womb. And in recent years, scientists poring over gigabytes of genetic sequencing data have seen other tantalizing hints of endogenous retroviruses turning useful.


And other mammalian species have utilized the same approach.

A study last month also suggested that this viral DNA is being used to help us fight viral infections. Sort of a molecular “fight fire with fire” approach.

The new twist on the old adage here seems to be: “If life gives you lemons, make antibodies to lemons.”


Read more of Dr. Donnelly’s “Reflections Of A Grinder” here.