Consider the four populations depicted in the following diagram: A, A+, B− and B. Each bar represents a distinct group of people, with the group's size represented by the bar's width and the happiness of each of the group's members represented by the bar's height. Unlike A and B, A+ and B− are complex populations, each comprising two distinct groups of people. It is also stipulated that the lives of the members of each group are good enough that it is better for them to be alive than for them to not exist.