we consider a species that possesses ouensive weapons capable of inflicting serious injuries. We assume that there are two categories of conflict tactics: "conventional" tactics, C which are unlikely to cause serious injury, and "dangerous" tactics, D, which are likely to injure the opponent seriously if they are employed for long. (Thus in the snake example, wrestling involves C tactics and use of fangs would be D tactics. In many species, C tactics are limited to threat displays at a distance, without any physical fighting. We consider a conflict between two individuals to consist of a series of alternate "moves". At each move, a contestant can employ C or D tactics, or retreat, R. If a contestant employs D tactics, there is a fixed probability that his opponent will be seriously injured: a contestant who is seriously injured always retreats. If a contestant retreats, the contest is at an end and his opponent is the winner. A possible conflict between contestants A and B can be represented in this way: A's move CCCCCCCCCCCDCCCCCCCD B's move CCCCCCCCCCCDCCCCCCCR If a contestant plays D on the first move of a contest, or plays D in response to C by his opponent, this is called a "probe or a "provocation". A probe made after the opening move is said to "escalate" a contest from C to D level. A contestant who plays D in reply to a probe is said to "retaliate". In the example shown above, A probes on his twelfth and twentieth moves; B retaliates after the first probe, but retreats after the second, leaving A the winner. At the end of a contest there are "pay-offs" to each contestant. The pay-offs are taken as measures of the contribution the contest has made to the reproductive success of the individual. They take account of three factors: the advantages of winning as compared with losing, the disadvantage of being seriously injured, and the dis- advantage of wasting time and energy in the contest. Table 1 Average Pay-offs in Simulated Introspecific Contests for Five Different Strategies Opponent "Mouse" "Hawk" "Mouse" "Bully" "Retaliator" 29.0 19.5 19.5 "Hawk" 29.0 80.0 -19.5 "Bully" -18.1 80.0 4.9 41.5 11.9 "Retaliator" 29.0 -22.3 $7.1 29.0 "Prober-Retaliator" 56.7 - 20.1 59.4 26.9 Contestant receiving the pay-off 74.6 "Prober Retaliator" 17.2 -18.9 11.2 23.1 21.9