the striped mouse ("rhabdomys pumilio") is group living with one single breeding male and up to four communally breeding females per group. groups typically contain several philopatric adult sons (and daughters) that are believed not to breed in their natal group and all group members participate in territorial defence. when aggression in wild group-living male breeders was tested in a neutral test arena, they were nearly five times more aggressive towards their neighbours than towards strangers, leading to the prediction that neighbours are the most important competitors for paternity. using a molecular parentage analysis it was shown that 28% of offspring are sired by neighbouring males and only 7% by strangers.