This is a theory that humans are inherently peaceful and are corrupted by modern society and economic systems.
It’s mainly attributed to the French philosopher Jean-Jacques Rousseau, who wrote in his Discourse on the Origin of Inequality:
…nothing is so gentle as man in his primitive state, when placed by nature at an equal distance from the stupidity of brutes and the fatal enlightenment of civil man
And in The Social Contract:
Man is born free, and everywhere he is in chains. Those who think themselves the masters of others are indeed greater slaves than they.
Many have criticized this theory, stating that it presents an idealized version of primitive man, who they claim was every bit as jealous and competitive as modern man.
The novelist Michael Crichton gave a speech in 2003 where he summed up the opposition argument:
The Maori of New Zealand committed massacres regularly. The dyaks of Borneo were headhunters. The Polynesians, living in an environment as close to paradise as one can imagine, fought constantly, and created a society so hideously restrictive that you could lose your life if you stepped in the footprint of a chief. It was the Polynesians who gave us the very concept of taboo, as well as the word itself. The noble savage is a fantasy, and it was never true. That anyone still believes it, 200 years after Rousseau, shows the tenacity of religious myths, their ability to hang on in the face of centuries of factual contradiction.