There was a time when hominoid species other than our own - homo sapiens sapiens - lived simultaneously in the vicinity of our ancestors [32]. Somewhat mysteriously our species became the only species to survive, while other hominoid (Neanderthals, e.g.) became extinct.
There are different theories accounting for this paleoanthropological conundrum. A convincing hypothesis is that homo sapiens sapiens must have some very special and superior mental abilities. The remains of highly complex ritual paintings show our ability to use symbols, and this may be the key ability. Using symbols is definitely a relevant factor: other hominids may also have had articulated language skills used to achieve complex cooperative tasks (highly coordinated hunting, for instance), however, as far as the ability of manipulating symbols is concerned, they were probably light-years behind our ancestors. For one thing, the language skill of Neanderthals (and perhaps other intelligent animals) may have been enough for them to achieve complicated hunting, but it was probably far too poor for them to talk about abstract issues and to accomplish more complicated mental tasks. This speculation is based on their ultra-simplistic cultural behaviors in comparison with ours. While Neanderthals did bury their dead, they probably did that simply out of worldly concerns -- to keep other predators away [32]. It is humans who can give, and in fact need, an elegiac address in a funeral. It is humans who know what to say and what not to on account of respect, contempt, or cultural taboos in such situations. While other animals run away from danger, or toward food and mates, due to instincts or conditioned experiences, humans ponder which word should be used to avoid embarrassment.
In fact, the ability to use symbols indicates a central concern of the human being -- meaning, which we tend to think of as an inherent property of symbols. These seemingly perpetual symbols offer us something to ponder; to ask questions about; and to answer. It has become very difficult for us to think of life without symbolic manipulation, for our lives are so bound to our way of making meaning by way of symbols. Without symbols, our lives would be much more ephemeral. Indeed, our species should have been called homo sapiens significans -- the meaning-making man instead of homo sapiens sapiens -- the intelligent man.