I believe word of mouth has evolutionary origins. Put simply, the human race benefited from telling family and friends about where the best roots and berries could be found, where the year around waterhole was, or where the best place to surprise an unsuspecting deer were. We share because we want to do good. And because deep in our minds we think we would get the favour back when in need – reciprocity in effect. So, we had pragmatic reasons for sharing. And this evolutionary advantage has persisted, and we are hard-wired to share tips. So, word of mouth continues and flourishes like never before.
In a way, something that goes viral can be seen as digital word of mouth. And thanks to the network effects of the Internet, the power of it is manifold. It can spread to innumerous people in the blink of an eye, and all across the world. It has been freed from time and space.