or one seasonal cycle. Secondly, there must also be a higher frequency of association (spatial proximity) between the bonded-pair individuals than there is with other individuals. Paternal care of offspring is a relatively uncommon trait in primate social systems; however, the monogamous mating system often observed (though it should not be assumed) in pair-bonding generates an equal variance for offspring success for both pair members. Thus, paternal involvement in off-spring rearing is much likelier to be observed in primate species where pair-living occurs. Examples of pair-bonded primate species: titi monkeys, owl monkeys, some species of marmosets and tamarins, many species of siamangs and gibbons One-female-multi-male groups are composed of one reproductive adult female and two or more adult male partners in the group. If there are other associated females within the group, they will likely have their reproductivity suppressed either via agonistic behaviours (aggressive and submissive interactions) or olfactory signals (such as pheromones). This social system promotes cooperative breeding (or alloparenting), where the non-breeding individuals assist in providing care for the off-spring produced by the main breeding female. Examples of one-female-multi-male structured primate species: many species of tamarin and marmoset One-male-multi-female groups are usually characterised by a single resident male who defends a group of (often related) adult females against males from outside the group. While tenure ship is held, this form of social organisation allows a male exclusive access to reproductive females for breeding purposes. A resident male often suffers challenges from extra-group males (perhaps belonging to all-male bachelor groups) whereby these males may attempt takeovers with the goal of gaining sole access to the reproductive females. A takeover by a new resident male could lead to infanticide (infant killing). This behaviour is interpreted as a strategic attempt to bring females back into estrous, which allows mating opportunities to occur sooner for the new resident male. Examples of one-male-multi-female structured primate species: some species of gorillas, numerous colobine and guenon species, patas monkeys, howler monkeys Multi-male-multi-female social systems are characterised by associations between larger numbers of individuals forming groups. Since individuals are able to mate with multiple partners, paternity is often hidden or skewed which helps ensure the survival of off-spring. A variety of social relationships and bonds exist among multi-male-multi-female group members. For instance, some research has led to observations of dyadic relationships, or friendships. These friendships are more moderate forms of the pair-bonded social structures, existing within