  Whatever term is used, the important point is that behaviours that benefit both self and others can evolve much more easily than altruistic behaviours, and thus require no special mechanisms such as kinship. The reason is clear: organisms performing such behaviours thereby increase their personal fitness, so are at a selective advantage vis-a-vis those not performing the behaviour. The fact that the behaviour has a beneficial effect on the fitness of others is a mere side-effect, or byproduct, and is not part of the explanation for why the behaviour evolves. For example, Sachs et al. (2004) note that an action such as joining a herd or a flock may be of this sort; the individual gains directly, via his reduced risk of predation, while simultaneously reducing the predation risk of other individuals. By contrast with an altruistic action, there is no personal incentive to ‘cheat’, i.e., to refrain from performing the action, for doing so would directly reduce personal fitness.