The second explanation involved forgetting or obliviousness. A mother in Illinois said: “My husband is a participatory and willing partner. He’s not traditional in terms of ‘I don’t change diapers.’ But his attention is limited.” She added, “I can’t trust him to do anything, to actually remember.”

A dad in San Francisco said that many of the tasks of parenting weren’t important enough to remember: “I just don’t think these things are worth attending to. A certain percentage of parental involvement that my wife does, I would see as valuable but unnecessary. A lot of disparity in our participation is that.”

Finally, some men blamed their wives’ personalities. A San Diego dad said his wife did more because she was so uptight. “She wakes up on a Saturday morning and has a list. I don’t keep lists. I think there’s a belief that if she’s not going to do it, then it won’t get done.” (His wife agreed that this was true, but emphasized that her belief was based on experience: “We fell into this easy pattern where he learned to be oblivious and I learned to resent him.”)

A father in Portland , Ore., confirmed that his wife takes on more but said: “It has to do with her personality. She always has to stay busy. No matter what day of the week it is, she has a need to be engaged, to be doing something.”

Many mothers told me they had tried to change this and had aired their grievances with their partners, only to watch as nothing changed. A mother in Queens said she spent three years trying to get her husband to do more before coming to terms with the fact that maybe it was never going to happen. “He notices the unfairness, but he just accepts it as something we have a disagreement about,” she said. “How much convincing of the other person can you do?”

All this comes at a cost to women’s well-being, as mothers forgo leisure time, professional ambitions and sleep. Wives who view their household responsibilities “as unjust are more likely to suffer from depression than those who do not,” one study says. When their children are young, employed women (but not men) take a hit to their health as well as to their earnings — and the latter never recovers. Child-care imbalances also tank relationship happiness, especially in the early years of parenthood.

Division of labor in the home is one of the most important gender-equity issues of our time. Yet at the current rate of change, MenCare, a group that promotes equal involvement in caregiving, estimates that it will be about 75 more years before men worldwide assume half of the unpaid work that domesticity requires.