Only HUMANS can speak, only humans can write. That is why it is called a human activity. And when they speak, they speak because of something worthwhile. They speak because of their plans, their activities now and in the future. Either they can speak good things or injuriously with the others.
We tend to live because of communication, and if communication doesn't exist, life doesn't matter at all. Life would be meaningless. In this world where communication is free, there is still miscommunication. So how much more when humans cannot express their things through communication? Life would be miserable. Truly, communication is a human activity.