When Americans imagine creating conditions for female success in the workplace, paid maternity leave is often high on the priority list.

This thinking, however, is outdated and wrong. Gender-equal paid leave not only gives all parents the opportunity to care for and bond with their children — it helps ensure that women reach their full potential and creates the conditions for a more equitable, prosperous world.

In the #MeToo era, many ask why American sexual arrangements are so strained. One key reason is an antiquated division between men and women that begins at birth. From the cradle, men are conditioned to associate nurturing and care with female figures — and to devalue the unpaid work that women shoulder disproportionately. This normalizes and sustains gender inequality in a way that hurts everyone: mothers, fathers, children — and society as a whole.

In the #MeToo era, many ask why American sexual arrangements are so strained. One key reason is an antiquated division that begins at birth.

The United States is one of only a very small handful of countries in the United Nations that lacks a national paid parental leave law — putting it in the company of countries like New Guinea, Lesotho and Suriname. According to PL+US: Paid Leave for the United States, a non-profit advocating for paid family leave, a quarter of new moms in the U.S. return to work 10 days after childbirth. For men, that figure is 70 percent — a situation not only unhealthy for child development, but reinforcing of old-fashioned gender roles.

The good news is that several states, including California, Rhode Island, New Jersey and New York, are now leading the way to change the harmful notion that caregiving is primarily a woman’s responsibility. It’s time for the federal government to get on board with an equitable, paid family leave policy.

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So why is it still so hard to see fathers as equally responsible for the early care of children? Part of it has to do with a quirk of human evolution. A baby guinea pig is born open-eyed and ready to walk, and a newborn blue wildebeest can outrun a hyena within a day. The human infant, in contrast, is born helpless. A baby needs constant supervision and strong caregiver investment.

Even among primates, the human baby is an outlier. A human fetus would have to gestate for up to 21 months to reach the developmental stage of a newborn chimpanzee. With its large head encasing a supersized brain, the human baby is born at an early stage of development: Otherwise it couldn’t squeeze through the birth canal.

So why is it still so hard to see fathers as equally responsible for the early care of children? Part of it has to do with a quirk of human evolution.

For much of human history, the birth mother has born the brunt of infant care because it is she who gets pregnant and breastfeeds this helpless creature. The cultural biases of patriarchy have tended to designate women as primary caregivers — and secondary human beings.

Starting with the Industrial Revolution, however, when women began to work in factories, old sexual arrangements began to change. This trend accelerated with advances in family planning technology and the flood of women into the workforce during World War II. Women’s liberation movements pried open previously locked doors of human endeavor, from university education to political participation to paid work once considered the sole domain of men.

Today, the human female is no longer condemned to a constant state of pregnancy during reproductive years and burdened with the care of a steady stream of infants and young children. She can be a full participant in all aspects of society, including the job market.

Yet the American workplace remains trapped in the past. Today’s families rely on the income of both parents and require the caregiving investments of moms and dads. While birth mothers need to recover physically from the impact of pregnancy and delivery, caregiving and bonding are critical activities for all parents, whether kids are biological offspring, born through surrogates or adopted.

Limiting the participation of men in early childcare actually mirrors the historic exclusion of women from participating in work outside the home. Not long ago, many considered it “unnatural” for women to work in an office or manage a career.

That prejudice has faded. But men, in contrast, are still commonly considered less naturally equipped to care for young children. Sociologists call this “trained incapacity.” In other words, men are seen as less able to care for babies because traditionally they have not been required to do it. Yet the rise of stay-at-home dads, who have doubled in number since 1989, proves that guys have plenty of caregiving capacity. Many feel fulfillment and pride in using it.

Right now, the U.S. Family and Medical Leave Act of 1993 guarantees 12 weeks of job-protected time off equally to many American moms and dads. The upside is that the policy treats both parents the same. But the harsh downside is that the leave is unpaid and unaffordable to most but the affluent. Men, in particular, are less likely to take leave that is unpaid to care for children. The law also does not even apply to many types of employees, including the growing cohort that works 25 hours or less.

The American public wants paid leave for parents — not just for moms. Polls show that the majority of both Democrats and Republicans support it. But business lobbies, with their deep-pocketed influence on politicians, have stood in the way of progress.

Some companies try to respond to modern conditions. Many others, however, have adopted “primary-caregiver” policies that recall the “Mad Men” era.

Some companies try to respond to modern conditions. Many others, however, have adopted “primary-caregiver” policies that recall the “Mad Men” era, when men were assumed to have few, if any, nurturing responsibilities. This reinforces an outdated homemaker/breadwinner model that carves out different identities and possibilities for men and women.

Companies with such policies are now under legal fire. Just ask JPMorgan Chase, the subject of a discrimination charge filed by the American Civil Liberties Union on behalf of a male employee who received a mere two weeks paid leave while mothers received 16. Or, Estée Lauder, which is paying $1.1 million to settle a class-action lawsuit filed by the Equal Employment Opportunity Commission for allowing only women to claim “primary caregiver” status and providing fathers with less leave and fewer benefits.

Can businesses afford to give men equal paid time off for children? The answer is yes. In 2004, California implemented a paid family leave policy, and studies now show that the change has had a neutral or positive effect on productivity, employee morale and turnover. Paid leave abuse has also been found to be rare.

Research shows that when dads take time to care for infants, moms can get back to work sooner and even earn more, thus helping them to progress in their careers. In addition, having fathers take part in early childcare may ultimately help reduce the gender wage gap.

Some companies are figuring out that providing equal leave is both good for employees and signals social responsibility. Etsy, for example, now allows six months of parental leave for each parent, to combat the “unconscious bias” against women and mothers in the workplace. Other companies, including American Express, Bank of America and Twitter have rolled out gender-blind policies.

Way back in 1976, Dorothy Dinnerstein, a feminist psychologist, wrote a classic book, “The Mermaid and the Minotaur,” arguing that excluding men from the care of babies is detrimental to human relations and has the pernicious effect of alienating men from their human nurturing capacities. If men shared equally in caregiving responsibilities, Dinnerstein showed, they would likely be less hostile to women and value the opposite sex more fully.

America has some serious catching up to do on equitable parental leave. Fortunately, we can learn from experiments undertaken in other countries. Some Scandinavian countries, for example, have extended maternity leave to long periods without allowing fathers equal time — which can have a negative impact on female careers and the hiring of women. That’s why countries like Iceland and states like California and New York have decided to simplify things with policies that treat parents equally.

In the 21st century, both men and women are needed in the workplace and the nursery. When the male hand rocks the cradle, too, the whole world wins.