This is the 21st century. Are we really still talking about "natural imperatives"? If nothing else, note that women are having fewer and fewer children, later and later - clearly, they are feeling this "natural imperative" less and less.
Traditional gender roles are unfair to women wanting to have a career, unfair to men who want to stay home with the kids, and far more rigid than needed. Having some "standard patterns" makes sense, but there should be more than one, and the freedom to deviate from those.