This 2017 German human study explored the relationship between birth stress and handedness. The authors summarized previous research which, among other points, estimated epigenetic contributions to handedness as great as 75%.
The study hit a snag in its reliance on the sixty participants (average age 24) completing, with the assistance of their parents and medical records, a 24-item questionnaire of maternal health problems during pregnancy, substance use during pregnancy, and birth complications. The subjects didn’t provide accurate information. For example:
- Only one of the subjects reported maternal alcohol use during pregnancy. An expected number would have been 26.
- None of the subjects reported maternal mental illness during pregnancy. An expected number would have been at least 7.
The subjects’ parents willingly misled their children about facts of their child’s important earliest development periods. The absence of evidence greatly increased the difficulty for researchers and individuals in determining causes of epigenetic effects still present in the subjects’ lives.
http://www.tandfonline.com/doi/full/10.1080/1357650X.2017.1377726 “DNA methylation in candidate genes for handedness predicts handedness direction” (not freely available)