ENVIRONMENTAL-INFLUENCES THAT MAY PRECEDE FERTILIZATION - A FIRST EXAMINATION OF THE PREZYGOTIC HYPOTHESIS FROM MATERNAL AGE INFLUENCES ON TWINS

The prezygotic hypothesis considers the possibility that development i s subject to environmental influences on the oocyte prior to conceptio n. Such influences may occur in the maternal grandmother's uterus wher e oogenesis is completed or in the mother before fertilization. Accord ing to this hypothesis, the separate eggs from which DZ twins are deri ved may be sensitive to microenvironmental variations within an ovary. As a first approach, we examined same-sex MZ and DZ twins for materna l age effects on differences between pairs in cognitive and behavioral traits. While no differences between MZ and DZ pairs were found that would indicate a major effect of the prezygotic environment, suggestio ns are made for further experimental studies of this unexplored questi on in human development.