Evolutionarily Stable Strategy<\/a> (ESS) in which a population of animals aggressively protects their territory and retreats when they enter the territory of another aggressive animal. The strategy is only stable if the whole animal population sticks to it.<\/p>\n\n\n\nRead more about the evolutionary need for aggression, including territorial aggression.<\/p>\n\n\n\n\n\n\n\n
The Need for Aggression<\/h2>\n\n\n\n
A population of animals actually needs a particular balance of aggression and pacifism in order to be stable\u2014too many aggressive (selfish) individuals will constantly fight each other, and too many peaceful individuals will be easily overpowered and exploited by a few aggressive ones. A stable population is the best situation for selfish genes trying to survive through as many generations as possible, without being overwhelmed by other types of animals. <\/p>\n\n\n\n
Animals will naturally compete with one another<\/strong>\u2014there are only so many resources to go around, so only a limited number of genes\u2019 hosts can reproduce. <\/strong>Members of different species may compete for various things\u2014for instance, blackbirds and moles might compete for earthworms\u2014but members of the same species will be in much more direct competition. This is because they tend to live in the same environment and need the same things, including food sources and mates.<\/p>\n\n\n\nGiven that fact, it seems logical that the best way to preserve one\u2019s own genes is to kill\u2014and possibly eat\u2014your rivals. However, while murder and cannibalism do happen in nature, it\u2019s not as common as an uninitiated observer might think.<\/p>\n\n\n\n
The problem is that fighting has great costs associated with its potential benefits. <\/strong>First of all, fighting takes a great deal of energy that might be better spent looking for food or breeding. It also naturally carries the risk that you\u2019ll wind up dead or maimed instead of your rival. A less direct, but still very real risk, is that by eliminating one rival you accidentally help another who was also competing with the individual you killed. <\/p>\n\n\n\nTherefore, before animals fight in earnest, they have to somehow weigh the risk against the benefits. Fighting another member of one\u2019s own species is extremely risky, since they\u2019re likely to have similar physical abilities. In fact, animals of the same species usually \u201cfight\u201d in a way that\u2019s comparable to boxing or fencing: There are rules, it\u2019s clear when the bout is over and who won it, and (barring an accident) neither party gets seriously hurt.<\/p>\n\n\n\n