In their Essay 'Can evolution explain how minds work?' (Nature 458, 832–833; 2009), Johan Bolhuis and Clive Wynne use Darwin's claim that there is “no fundamental difference between man and the higher mammals in their mental faculties” to explain how people have gone down the wrong path in studying cognition. But in homing in on examples of convergent evolution, in which humans and some distantly related species such as songbirds seem to have come up with similar solutions to the same problem, Bolhuis and Wynne neglect one key feature that distinguishes humans from all other animals.
The feature that is peculiar to humans is their understanding about the causal interactions between physical objects (see, for example, L. Wolpert Six Impossible Things Before Breakfast; Faber, 2006). For example, children realize from an early age that one moving object can make another move on impact. It is this primitive concept of mechanics that is a crucial feature of causal belief, and that conferred an advantage in tool-making and the use of tools — which, in turn, drove human evolution.
Animals, by contrast, have very limited causal beliefs, although they can learn to carry out complex tasks. According to Michael Tomasello (The Cultural Origins of Human Cognition; Harvard Univ. Press, 1999), only human primates understand the causal and intentional relations that hold among external entities. Tomasello illustrates this point for non-human primates with the claim that even though they might watch the wind shaking a branch until its fruit falls, they would never shake the branch themselves to obtain the fruit. Some primates are, nevertheless, at the edge of having causal understanding.
Once causal belief evolved in relation to tools and language, it was inevitable that people would want to understand the causes of all the events that might affect their lives — such as illness, changes in climate and death itself. Once there was a concept of cause and effect, ignorance was no longer bliss, and this could have led to the development of religious beliefs.