Wrangham (2009) & McClenon (2006) describe the campfire in evolutionary history as something like a social nexus. Wrangham says it’s where hominids came to & learned to tolerate each other. McClenon says it’s where hominids developed their relaxation skills, by zoning out staring at the fire (it’s not as vapid as it sounds when I put it that way). In building his argument for humans as a “eusocial” species, E.O. Wilson (2012:31) refers to the campfire as a “nest.”
There is an a priori reason for believing campsites were the crucial adaptation on the path to eusociality: campsites are in essence nests made by human beings. All animal species that have achieved eusociality, without exception, at first build nests that they defended from enemies. They, as did their known antecedents, raised young in the nest, foraged away from it for food, and brought the bounty back to share with others.
He goes on to explore why chimps & bonobos did not develop eusociality while their closest living relatives did (p. 42):
Why is a protected nest so important? Because members of the group are forced to come together there. Required to explore and forage away from the next, they must also return. Chimpanzees and bonobos occupy and defend territories, but wander through them while searching for food. The same was probably also true of the australopith and habiline ancestors of man. Chimps and bonobos alternatively break into subgroups and re-aggregate. They adverstise the discovery of fruit-laden trees by calling back and forth but do not shre the fruit they pick. They occasionally hunt in small packs. Successful members of the pack share the meat among their fellow hunters, but charity mostly comes to an end there. Of greatest importance, the apes have no campfire around which to gather.