The association between the number of children in the family and the heights of sons before, during and after the fertility decline

A negative association between the number of children in a family and the heights of the children has been shown many times for 20th century populations. The causes behind this association are not known but could include resource scarcity in large families or that families with different numbers of children are different also in other, observable or unobservable, ways. This study investigates the causes behind the negative association between family size and child heights by examining the association among men born 1797-1950. This is done using longitudinal, individual level data on socioeconomic background, household structure, family relations and heights of conscripts. The results show that the causes behind the negative association are manifold and complex, and their relative importance having changed over time. Children with many siblings were shorter than others, at least from mid-19th century onwards. Resource dilution within families is probably one of the explanations for this negative association. But the association seems to have been different in landed families as compared to others, and also different in families with unusually few or many children. The explanations needed to explain the negative association between sibship size and child outcomes differ depending on the societal and historical context.