"The philosophy of M. Rousseau of Geneva is almost the reverse of Hobbes's," wrote the authors of the Encyclopédie (as quoted by Michael Doyle in Ways of War and Peace, p.137).
Although Doyle says that the Encyclopédie exaggerated, judging from Rousseau's Discourse on the Origin and Foundations of Inequality, which I've been reading, the encyclopedists' view is unsurprising. Rousseau criticizes Hobbes by name in the Discourse, and in contrast to Hobbes's famous description of the state of nature as unremittingly violent, Rousseau supposes a state of nature in which humans are, by and large, peaceful: "...wandering in the forests, without industry, without speech, without shelter, without war, and without ties, with no need of his fellow men, nor any desire to harm them, perhaps without ever even recognizing anyone individually, savage man, self-sufficient and subject to few passions, had only the sentiments and knowledge appropriate to that state...."
The evidence that exists about 'primitive' humans suggests that the reality lay somewhere in between Hobbes's war-of-all-against-all and Rousseau's peaceful 'savage'. Referencing Lawrence Keeley's War before Civilization (1996), Joshua Goldstein writes in War and Gender (2001), p.26, that the evidence, while "very spotty," is "consistent with (but not proof of) the presence of warfare at least sporadically throughout all periods of prehistory.... A new and growing...body of tangible evidence -- ranging from discernible fortifications around settlements to remnants of weapons and the residue of injuries on bodies -- suggests the presence of war before agriculture."
1. Rousseau's Political Writings, ed. A. Ritter and J.C. Bondanella, trans. Bondanella (Norton Critical Edition, 1988), pp.31-32.
Added later: "To a number of readers, it has seemed that Rousseau wrote the Second Discourse for no other purpose than to refute, point by point, the Leviathan's argument regarding the human condition in the state of nature (Melzer 1990; Plattner 1979)." -- D.N. Levine, Visions of the Sociological Tradition (1995), p.174.