Social dilemmas in class-structured populations

动植物经常面临两难境地。例如，一只动物可能不得不在保持现有食物来源(可以说是“肯定的事情”)和放弃食物来源去寻找更丰富的食物来源(可能是一场“赌博”)之间做出选择。同样，植物可能不得不在使用从太阳获得的能量来生产种子和使用同样的能量来长高之间做出选择。当然，道路上的每一个岔路口都会对想象中的动物或植物的进化成功产生影响。在某些情况下--实际上是一些最有趣的情况--留下或离开(生长或繁殖)的决定会产生连锁反应，同时改变附近许多个体的进化成功。用生物学的术语来说，这些困境被认为具有“社会后果”，因此它们被恰当地称为“社会困境”。

Animals and plants routinely face dilemmas. An animal, for instance, might have to choose between remaining committed to its present source of food (a "sure thing" so to speak) and leaving the food source in search of a richer one (possibly a "gamble"). Likewise, a plant might have to "choose" between using the energy it receives from the sun to produce seeds and using that same energy to grow taller. Of course, each fork in the road has an effect on the evolutionary success of the imaginary animal or plant. In some cases -- actually some of the most interesting cases -- decisions to stay or leave (grow or reproduce) have ripple effects, simultaneously altering the evolutionary success of a number of individuals nearby. In biological terms, these dilemmas are said to have "social consequences" and so they are appropriately dubbed "social dilemmas."