However, things are not as simple when we consider more complicated cases. At least one study I know of considers this for animals. Take a rat and teach it that if it goes to one bucket, it gets a big treat, and if it goes to another, it gets a small treat. If the payoff difference is small, the rat takes the safer path. However, if the payoff difference is large enough, the rat will take the more dangerous path.
Humans are no different.
Given a clear life or death choice, they almost always choose life. However, give them a choice that affects the chance of death, and it is not so clear. There is a long list of things that people do where they are willing to accept an increase in their risk of death in exchange for some sort of a payoff. I'm not up on the evolutionary arguements for this behavior, but I suspect they go something like this. Organisms are in competition with eachother.