Any zoo-goers so unlucky as to be on the receiving end of a poop-tossing chimpanzee may be excused for taking a dim view of that particular form of monkey mayhem. But don't let the gross-out aspect of the situation cloud your judgment about the perpetrator: New research suggests that a primate's ability to throw an object is actually a solid indicator of intelligence.
Bill Hopkins of Emory University and his collaborators make that argument in a new paper published in the Philosophical Transactions of the Royal Society B. Among other things, they find major overlap between brain areas which distinguish right- and left-handed throwing chimpanzees and the regions of the cortex involved in language processing by humans. The researchers concluded that the chimps which were better throwers also possessed more developed left brain hemispheres, the area where we process speech.
From a neurological perspective, throwing is considered to be a complex activity. It demands coordinated precision in timing the velocity as well as the release of a projectile in relation to the speed of movement and distance of the target. That ability to process a more complicated set of circumstances was manifested in the finding that the better-throwing chimpanzees also demonstrated more developed communication abilities than chimpanzees which hadn't developed that ability
So it is that throwing involves a large degree of planning by chimps, who were found to be quite aware of a connection between their actions and their ability to affect - or manipulate - humans.
In a related observation, the study's authors noted that the throwers and non-throwers weren't physically different from each other, a finding that would suggest a trait developed for self-expression rather than for hunting.
"What appears to be the main reward for throwing is the simple ability to control or manipulate the behaviour of the targeted individual (ape or human). For example, in our laboratory, chimpanzees will patiently wait for strangers or visitors to approach and then will throw at them. They do not conceal their intentions and they will often stand bipedal and threaten to throw by cocking their arm with the projectile in their hand in preparation for throwing. The passers-by can see this and will often try and negotiate with the chimpanzees to put down the projectile, or they will try to trick the ape by stopping, then dashing rapidly past the ape enclosure. This seems to be the reaction the apes hope to get from the humans and, in operant conditioning terms, is the only 'reward' the chimpanzees receive for throwing."