The chimpanzee troop contentedly enjoyed their stand of trees. There were bananas and termites enough for everyone. Nearly everyone had a branch, even the lower ranking chimps. And then it happened.
Somewhere out in the vastness of the universe, a star had exploded centuries ago, and just now the cosmic radiation from the super nova reached Earth. No one felt anything, but as the radiation penetrated the skulls of the chimpanzees, it reconfigured their neurons and made them ever so slightly more intelligent. It wasn't much of a boost, but it was a boost. In short, they were now like us.
One chimpanzee, previously contented with his branch, noticed that another chimpanzee had a better branch. Rather than jostle about and take the other branch, this newly advanced chimpanzee pulled a banana from his bunch and offered it to the other chimpanzee in exchange for his branch. The other chimpanzee accepted and the two swapped places. Other chimpanzees observed this exchange, something that was novel to their troop, and began to look at the branches of the other chimpanzees, comparing them to their own, and in moments, chimpanzees were bargaining with one another over swaps of position in exchange for fruit.
Quickly, the chimpanzees expanded upon their new game. Some chimpanzees held out for best offers while others went a step beyond and began claiming branches in empty trees as their own in hopes of flipping those branches for bananas. As the game grew more complex and competition for branches increased, it soon became the case that such a large number of bananas were needed to purchase a branch, that chimpanzees resorted to borrowing bananas from one other to amass payment for branches. When this became inadequate, future bananas were promised in exchange for branches, condemning many chimps to long periods of banana gathering just to keep the branch that sat upon.
No one knows exactly when it happened, but at some point along the way the chimpanzees began to run out of surplus bananas. Sure, there were enough bananas to eat, but they couldn't eat those bananas because they had all been promised in exchange for branches. Some chimpanzees could no longer find enough bananas to continue their payments on their branches. As was the rule, chimpanzees that did not make promised banana payments on branches were kicked off the tree and their branches went back to the banana lenders who now had more branches than they could sell. The excess of empty branches made all of the branches less valuable and this made the banana lenders nervous because the branches were now worth less than the bananas lent. Those lenders with bananas to lend stopped lending bananas. Branchlesss chimpanzees roamed the ground around the trees grumbling at their lot. Fear overcame the troop as each chimpanzee feared losing her own branch. Panic spread. It was as if a fire had consumed their stand of trees.
And then the radiation stopped.
As quickly as the small boost in intelligence came, it went. Each and every chimpanzee forgot what had happened. The branchless chimpanzees looked up at the empty branches. One by one they climbed up the trees and took a branch for themselves. The bananas were passed around. Happy sounds returned as they swung from branch to branch. Nearly everyone had a branch, even the lower ranking chimps. There were bananas and termites enough for everyone. The chimpanzee troop contentedly enjoyed their stand of trees.