The elephant-shrews or sengis (order Macroscelidea) represent a monophyletic radiation endemic to Africa with 15 extant species in four genera. Field studies of representatives from all four genera indicate that all are socially monogamous. Resource and female dispersion, indirect paternal investment and male mate guarding have been proposed as factors contributing to sengi monogamy. To better understand sengi social organization, we studied the behavioural ecology of the bushveld sengi Elephantulus intufi in Namibia. Radio-tags and direct observation were used to gather spatial and behavioural data during 5 months in 2000-2002. Bushveld sengis were distributed as monogamous pairs on exclusive territories, similar to other sengis. Maternal care was characterized by an 'absentee' strategy and there was no evidence of direct or indirect paternal care. Sengis share many life-history traits with small antelopes, including uni-parental monogamy. Unlike the antelopes, which exhibit strong pair bonds, bushveld sengi pairs spend little time in coordinated activities. Male mate guarding best explains why sengis are socially monogamous - a model largely developed from studies of small antelopes. The similarity in morphology, life history and behaviour among sengi species results in a distinctive adaptive syndrome, which explains the consistency of their social structure, even in the extremes of terrestrial habitats that they occupy. The degree of sengi social monogamy is labile, which is related to their weak pair bond, same-sex aggression and variable densities.