Human evolution seems to have begun with tools, language and hunting. Now it seems the silver medallist in these events is catching us up. Chimpanzees have long been recorded throwing with great accuracy in zoos as well as in the wild. For example, a chimp called Santino has been recorded as hiding stones out of sight from zoo staff and throwing them at visitors in a pre-planned campaign! Faeces and food are often used by other captive chimps in the significantly pre-planned behaviour. In the wild, too, humans or other chimps are targets, and never food species.
Previous interest in throwing by the chimpanzee has centred on the "cerebral plasticity" associated with chimps that learn to throw accurately. They develop larger cerebella (hind-brain). This study scanned white and grey matter of 78 captive chimps in the hope of locating increased WM (white matter) in those who learned to throw. Chimp "sophistication" and intelligence were also investigated. Various tests based on those given to children were carried out in the investigation. These were on spatial memory, invisible displacement of a food reward and causality of noise and visual stimuli. Cognition and comprehension tests concluded the physical examination.
Four frames that demonstrate a chimpanzee who is throwing a pipe towards a human in a tower above the subject. The chimpanzee stands, brings the PVC pipe back, and throws the object. Note that the force of the chimpanzee's throw actually causes him to leave the ground. This reflects the whole body function of throwing; Credit: Philosophical Transactions of The Royal Society B
Results produced the expected greater extent of white matter for throwing individuals. These individuals may have already had that amount of WM before the experiment, but the implication is there. Inferences of an associated connectivity change within the cerebral cortex were also found. The evolution of language and speech is thought to be associated with neural adaptations specifically gained from throwing, so this paper adds to that evidence. In a somewhat similar way, throwers were also found better at communication tasks, leading to a more successful competitiveness. However the chicken and egg situation comes to mind. We do not know which came first.
Other species have been investigated, but only chimpanzees seem to have underlying cognition associated with throwing ability. Their left cerebral hemisphere was probably specialised for planning complex motor actions before the proposed human/chimpanzee ancestor evolved. Aimed throwing may have changed our neural architecture and then aided in speech and language pre-disposition.
Fascinating conjecture from "man's closest relative." Obviously the research could gain much more from extending these experiments to solve find several answers such as that chicken and egg problem. And that reward the chimp gets when he harasses visitors with his "wicked" planning!