Are there sex differences in temperament?

Our research at Kaiser Permanente produced some interesting sex differences in infancy. For example, parents rated their four- month-old daughters as significantly more sensitive and fussy about wet diapers.

But the major sex differences in infancy were in the links between early temperament and later behavioral issues. Girls rated at 4 months by their parents as lower in frustration tolerance or adaptability (particularly to novelty) were more likely in later months to be seen as shy and fearful in strange places or experiencing sleep and separation difficulties. Boys in turn showed stronger associations between movement levels at 4 months and later assertiveness issues, such as rejection of play pens.

Are these true sex differences or cultural biases? Are parents more likely to continue to report shyness in their daughters, but deny it in their sons? Do parents hesitate to report a daughter's self-assertions. These are interesting possibilities. As yet, there are no clear answers.