The question how far the ontogeny of social behaviour shows similarities and to what extent it is genetically determined is investigated for 3 F2 canid hybrids of one litter by the example of contact play behaviour. It is known that jackals, especially the golden jackal (Canis aureus L.) display a number of differences in social behaviour and a very early ontogeny compared with the wolf (C. lupus L.) and the domesticated dog (C. I. forma familiaris). In this study behaviours were classified by timing the duration of single events from video records. The analysis bases on the duration of special patterns of behaviour and not, as is usually done, on single observations. Readiness to play is of special importance. It is measured by the number of plays initiated and behaviour during play. Whereas individual duration of play of these 3 F2 hybrids is greatly influenced by exogene factors, the maximum readiness to play, occurring over a marked time interval, seems endogenously determined. The different inborn development of readiness to play leads to very different frequencies of partner combinations during the various phases of development. Animals with much play initiative more often take part in contact play of their own accord. This establishes the order of frequencies of the playmates chosen. The frequency of successfully triggering contact play and the duration of the individual play initiative turn out to be a suitable measure of the — otherwise hardly recordable — genetically determined readiness to play.