We examine if parity progression ratios differ by the sex composition of previous children in contemporary and historical Sweden and Taiwan. We use longitudinal micro level data to follow the change in sex preferences over 200 years in Sweden and 100 years in Taiwan. We apply event history models, and interact transition to 3ird birth with sex composition and cohort to examine change over time. We find the gradual emergence of a mixed gender preference in Sweden over time. In Taiwan we find a transformation from a son preference system into some patterns of a preference for a mixed gender composition. We find that the mortality context is important for gender preferences, and that with increasing child survival the pattern change.