Conflict resolution has also been studied in non-humans, like dogs, cats, monkeys, snakes, elephants, and primates (see Frans de Waal, 2000). Aggression is more common among animal relatives and within a group, than between groups. Instead of creating a distance between the individuals, however, the primates were more intimate in the period after the aggressive incident. These intimacies consisted of grooming and various forms of body contact. Stress responses, like an increased heart rate, usually decrease after these reconciliatory signals. Different types of primates, as well as many other species who are living in groups, show different types of conciliatory behaviour. Resolving conflicts that threaten the interaction between individuals in a group is necessary for survival, hence has a strong evolutionary value. These findings contradicted previous existing theories about the general function of aggression, i.e. creating space between individuals (first proposed by Konrad Lorenz), which seems to be more the case in conflicts between groups than it is within groups.