Most primates live in groups consisting of several adult males and adult females (Melnick & Pearl 1987). By recording births to known females, relatedness via the maternal line can be reconstructed by human observers. However, when females mate with more than one male, all sexually active males have to be considered as potential sires. Paternity is uncertain to be identified by observation (Inoue et al. 1993), but can be determined using modern genetic techniques. Since paternity analyses were introduced into the field of primatology not earlier than at the beginning of the nineties (e.g., Martin et al. 1992, Inoue & Takenaka 1993), all previous studies on wild or free-ranging primates with multiple mating lacking the knowledge of paternity. For decades, all studies on kinship in primates were limited to maternal kin. Consequently, all individuals not maternally related were considered to be unrelated ignoring the proportion of paternally related individuals (cf. Kummer 1992). However, each individual shares on average 50% of its genes with the mother and the remaining 50% with its father. If we additionally consider the remarkable importance of maternal kinship in shaping female primate behaviour (see chapter 4-6, reviewed in Silk 2001), we still just know half of the story as we miss knowledge about the existence and the importance of paternal kinship. This thesis will investigate whether or not paternal kinship also influences female primate behaviour.

Determining the sire of an individual opens up revolutionary possibilities to answer questions which could not have been addressed before. One question of interest is related to male competition over females. Darwin (1871) already noted this type of sexual selection and named it intrasexual selection. The issue of male reproductive success has attracted researchers (e.g., de Ruiter et al. 1992), but it is still unclear for many primate species whether reproduction is equally distributed among sexually active males or whether reproduction is limited to some males (male reproductive skew) (Pereira et al. 2000). Only the latter situation where few or even one male monopolise/s all receptive females creates paternal kinship. Whether or not paternal kinship is existing among primates will be one of the topics addressed in this thesis.

Another question of enormous interest is to test whether kin selection theory also holds among paternally related individuals (Hamilton 1964). The impact of paternal kinship has been expected to be important (J. Altmann 1979), especially when male reproduction is skewed within the birth cohort considered resulting in paternal cohorts as infant tend to be sired by the same male. Whether paternal cohorts exist and whether the presence of paternal kin is also influencing the social structure has not yet been investigated. From kin selection theory (Hamilton 1964) it is expected, that, assuming costs and benefits being equal, paternal half-siblings should support each other to a similar extent as maternal half-siblings do, as they share the same degree of relatedness. This requires that individuals somehow discriminate their paternal siblings from non-kin, but whether primates are capable of paternal kin discrimination is questionable (Walters 1987).

The kinship structure within a social group depends at least upon two variables which also differ among species: (i) the mating system of the species and (ii) the migration system meaning which sex is the dispersing one.

The study species, the rhesus macaque (Macaca mulatta) has a promiscuous mating system, i.e., males and females mate with more than one sexual partner. Clearly, male and female reproductive decisions shape the kinship structure within a group. In other words, a different kin structure will result when the same pair of a male and a female reproduces together each year (resulting in progeny which will be full-siblings), when a female always reproduces with a different male (her offspring will be maternal half-siblings) or when a male fertilises a number of unrelated females (his offspring will be paternal half-siblings).

As in other macaques, the male is the dispersing sex, creating a group which is built by a core of maternally related females and their female descendants structured in matrilineal lineages(Melnick & Pearl 1987). Females live together with their kin and non-kin throughout their life. Males in contrast leave their natal group around puberty and spend most time of their reproductive life among unrelated individuals in a non-natal group. Investigating the effect of kinship, this study is therefore restricted to females which are the social core of a group and assuming male reproduction skew who are likely to have paternal kin to interact with. Therefore, females are likely to interact with both maternal and paternal kin, but also non-kin.