We are all hosts on a viral planet.

That’s my version of life.

In a paper published in the open access journal eLife this week, researchers say they have pinpointed what may well be one of evolution’s greatest copy mess-ups yet: the mutation that allowed our ancient protozoa predecessors to evolve into complex, multicellular organisms.

Thanks to this mutation – which was not solely responsible for the leap out of single-cellular life, but without which you, your dog and every creature large enough to be seen without a microscope might not be around – cells were able to communicate with one another and work together.

And, incredibly in the world of evolutionary biology, all it took was one tiny tweak. One gene, and complex life as we know it was born.

“It was a shock,” co-author Ken Prehoda, a biochemist at the University of Oregon, told The Washington Post.

“If you asked anyone on our team if they thought one mutation was going to be responsible for this, they would have said it doesn’t seem possible.”

The discovery was made thanks to choanoflagellates – tiny balloon-shaped creatures that are our closest living unicellular cousins – and a cool bit of evolutionary time travel known as ancestral protein reconstruction, which allows scientists to resurrect the genomes of long-dead creatures based on their modern descendants’ DNA.

In this case, the reconstruction took Prehoda and his colleagues back some 600 million years (day 3 on the religious time clock?), when ancient beings no bigger than a single cell swam through vast shallow seas covering what are now continents. There’s pretty much no fossil record from this period – what kind of fossil could be left by something smaller than a pinhead? – so insights into life at that time rely on researchers’ imaginations and intense scrutiny of modern DNA.

For this, the choanoflagellates were perfect. They’re single-celled organisms, but they occasionally work together in groups, swimming into a cluster with their flagella (tails) pointing outward like the rays of a sun. At the most basic level, this coordination helps the choanoflagellates eat certain kinds of food. But it’s also an example of individual cells coming together to work as one unit, kind of like – hey! – a multicellular organism.

Prehoda and his colleagues began to look into what genes could be responsible for allowing the choanoflagellates to work together.