While the mother-in-law to daughter-in-law link is surely the most complex, all in-law relationships come under tension as couples move through life together. The most frequent intra-familial flashpoints are religious celebrations and holidays. “If both sets of in-laws are adamant that you’re all going to theirs for Christmas, you’re going to have a problem,” says Martin Daly, a professor of psychology, neuroscience and behaviour at McMaster University, Canada and co-author of In-Law Relationships in Evolutionary Perspective. “Occasions like Christmas are a major point of conflict, because it’s where people are expected to be together.”
