Its not that simply that our brains are bigger that is producing these differences; instead, we are capable of greater levels of abstraction, intensity, and direction than other primates. Calvin talks about the Big Bang of the mind, but what caused it? A number of possibilities have been suggested over the years, but Calvin has his own intriguing idea: the structured, directed thought that distinguishes us from primates is a consequence of the development of structured, directed, and planned actions. Specifically, Calvin suggests that the activity behind throwing a spear for hunting is a good candidate.
We dont look at throwing a spear to hunt game as anything significant, but there is quite a lot more involved than there seems to be and nothing quite like it has been observed in other animals. Accurate throwing requires practice, coordination between several parts of the body, estimations of preys movement, predicted velocity of the spear, the ability to change plans in the face of novel situations, etc. None of this comes automatically and the entire suite requires a serious investment of coordinated resources but the payoff is at least as great.
Once such structured interactions in the brain are set up, though, they remain flexible enough to be useful in other situations and for other purposes. There is no planning out the hunt module that is only ever used for spear throwing; instead, the brain is set up to plan in general and this, in turn, can be used for much more than just hunting for example, the similarly complex structure of symbolic language and syntactic constructions.
All of this flexibility could, according to Calvin, offer us opportunities to influence our own long-term evolution. If we wish we might be able to push our brains along just as was done in the past by our development of spear-throwing skills. Of course, the ability carries great responsibility as well and it would be a serious mistake to act without knowing what we want and why. After all, it sometimes seems as though our mental abilities arent always up to the task of handling the technological world we have created already.