... and made a real mess of the place when one of them spotted the jar of pickles on the counter. They fought over it until one of them had almost all the pickles and the other one had a number of bruises and a tiny fragment of one pickle that the other chimp dropped by accident.
That would be the way it would happen if two chimps walked into a bar. Or imagine two chimps, and each finds a nice juicy bit of fruit out in the forest. And instead of eating the fruit, because they are not hungry, they carry it around for a while (this would never happen, but pretend) and then accidentally run into each other. What would happen? Same thing. Event though neither chimp actually needed the fruit and each chimp had its own fruit, the dominant chimp (between the two) would end up with both pieces of fruit.
This is why chimps could not possibly cooperate in any effort to scour the forest for various edible items, bring them all back to a central place, share and then cooperatively process the food items, and ultimately produce a meal that is eaten by all of the chimps on an as needed basis. Humans do that but chimps can't. Explain this and you explain one of the major features of human evolution...
Some of us think that about two million years ago, an ape-like hominid ancestral population for humans gave rise to individuals with the novel capacity to do the following:
1) Make and control fire;
2) Cook food on this fire; and
3) Cooperate enough that individuals could in fact bring food morsels to a central place for processing and sharing.
The consequences of this nexus of novelties would be significant. There would be much more energy in the environment available for consumption because cooking converts a lot of inedible biomass into edible biomass. This could supply the necessary nutrients for bodies to grow larger and be maintained at larger sizes, which might be useful in the predator-rich environment of Africa. Note that where we can determine cause of death for australopiths, or at least guess reasonably what it might have been, predators are typically involved. This seems to stop happening with the larger bodied Homo erectus following this transition.
Another consequence is the extra nutrition to support the growth and maintenance of a large, costly brain.
These early human ancestors would have to have a way of cooperating rather than (almost) always competing over things like food. This could result in behaviors supportive of more complex and sophisticated technologies being regularly used, as we in fact see in the archeological record. The novel food sources plus the additional technology together would support this species' movement into additional habitats previously not occupied by hominids. We also see this happening just at this time in the archaeological record.
For various reasons I won't go into here, this would also have surely changed the overall social organization among these hominids, and we suggest that this may have been the origins of something not entirely different from modern (more or less monogamous) marriage.
This is all well and good, but the real reason is in your other post about the dinner: beer. ;)
I like the paper, especially the phrase "underground storage organs".
Well, bonobos figured it out.