[Nagel 71] He also states that their existence cannot be explained by a physically reductive evolutionary theory. Nagel said: “Even in nature, it is not just perception and operant conditioning that have survival value. The ability to generalize from experience and allow these generalizations, or general expectations, to be confirmed or disconfirmed by subsequent experience is also adaptive. [Nagel 71] His argument can be summarized by saying that natural selection would favor creatures with a higher cognitive level. On top of that, higher level cognition justifies the need for a mind. Although this sounds good, it does not prove that high-level cognition causes or requires consciousness. This still leaves the possibility for life to function, simply without an operator, perhaps in the manner of a computer which can be programmed to run a task in a loop and continue to function without the intervention of an operator.