Abstrakt
Duplication theorem, proposed by Walter Toman, states that the couples whose birth order duplicates interpersonal patterns of the families the spouses come from (e.g., a couple consisting of older brother of a sister and younger sister of a brother - "complementary" sibling constelations) are formed more frequently and show higher degree of stability and satisfaction than the couples with non-complementary sibling constellations. However, empirical support for this hypothesis is rather ambiguous.
Here we tested the frequency of complementary and non-complementary couples while employing 3 datasets. Further, we tested whether the frequency of the couple's dissolution depends on sibling constellations of the partners.
We focused on heterosexual couples where both partners had only one sibling (N=601, 309 and 3212) to avoid potentially confounding variables such as family-size and classification of middleborns. We found that complementary couples are not more frequent as compared tonon-complementary couples.
In contrast, in two of the datasets, we found couples sharing the same birth order (i.e., homogamous couples) being significantly more frequent than non-homogamous couples. Pairs where partners shared some characteristics of their sibling constellation (birth rank and sex of the sibling) tended to be more frequent in the population.
However, the homogamous couples did not show lower levels of dissolution compared to the non-homogamous couples. Our results do not support Duplication theorem, and call into question its relevance for populations with a low fertility rates.