By “human” you mean clearly a quality bestowing some especial dignity and value. Such a quality cannot emerge from evolution ruled by “selfish genes”, as Richard Dawkins himself acknowledges.
Where does this especial dignity and value of humanity come from?
Well, Genesis has the merit to give a very clear answer to this question:
At a certain moment in history God declares Humanity to be in his Image (Genesis 1:26-27; 5:1-3). And this means nothing other than at this moment God defines the kind of body his Son will embody to incarnate.
Since this declaration it holds that:
Each creature with a human body (no matter of being black or white, literate or non-literate, born or unborn, religious or atheist, democrat or republican) is Image of God and is protected by God’s prohibition of homicide (Genesis 9:5-6).
This said, we would like to ascertain the moment when God declared humanity in His Image. According to Genesis this moment was followed by man receiving the knowledge about good and bad (Genesis 2:16-17), that is, awareness of being responsible for his own deeds. Now writing is motivated by the will of signing contracts, keeping registers and enacting laws (actions revealing sense of moral and legal responsibility). So we can safely state:
God declared humanity in His Image at latest when writing appears, that is, at 3,200 BC according to the available data.
As said above the Incas are creatures with a human body existing after God declared humanity in his Image. Therefore, each Inca is Image of God independently of his/her ability to knot cords.
Nonetheless, if you could make available remains demonstrating that such a system or another one, was used to sign contracts or enact laws before 3,200 BC, then we should predate the moment of God’s declaration of Humanity in His Image.