Desiree Cox

So in spite of the fact that we would think that we're 100% human, actually lots of our DNA, our genome, our sequences came from other places.

So while we don't actually have a number of how much of our DNA is human or not, because of course we share it with lots of other organisms in our evolution, we reckon about 8% at our current estimate actually came from viruses.

So at least 8% of us is not human in origin.

Yeah, it's fascinating.

There's a couple of things that we sort of look to as our supporting evidence for the fact that these are viral in origin.

The first of which is they have a viral genetic fingerprint.

So essentially, if we look at the sequences that we can find in our genome,

They have the same kind of structure in terms of the things that they are designed to make as viral proteins that we can find today.

The second is we see signatures of mutational decay.

So the viruses that have been with us the longest that we share with other organisms from our evolutionary history, we can map how those viral sequences have evolved through to our present day.

And that gives us a bit of a trajectory, a history, essentially, of how these things will have joined the genome in the first place and then what they look like now.

Yeah, absolutely.

So most of that mutation has been all about essentially inactivating those viruses.

So none of the viral sequences that we can detect in the human genome

should currently be capable of making viruses from those sequences.

So unlike a virus which infects our cells and copies itself and then turns itself into an infectious virus and goes on and infects the next thing, these sequences shouldn't be infectious anymore.

And a huge amount of that mutation that has happened has gone into essentially removing that infectious nature.

Yeah, it's interesting because this dynamic between viruses and the cells they want to infect has been probably a story as old as time.

Definitely there are even viruses that attack very small things like bacteria, for example.

In terms of when these things joined us as humans, this has been happening all throughout our history.