Claire Cain Miller in The New York Times (use the archive link to bypass the paywall):

When straight couples divide up the chores of daily life — who cooks dinner and who mows the lawn, who schedules the children’s activities and who takes out the trash — the duties are often determined by gender. Same-sex couples, research has consistently found, divide up chores more equally.

But recent research has uncovered a twist. When gay and lesbian couples have children, they often begin to divide things as heterosexual couples do, according to new data for larger, more representative samples of the gay population. Though the couples are still more equitable, one partner often has higher earnings, and one a greater share of household chores and child care. It shows these roles are not just about gender: Work and much of society are still built for single-earner families.