HUMANS LOVE TO FEEL as if we're controlling fate, but researchers say that we live for the unexpected. Brain neurons crave novelty. Luckily, there's an insurance policy that guarantees unscripted action: the family vacation.

The excitement comes back in a flash to Shannon Stowell. When he was eight years old, he and his family went on a fishing trip in the Colorado Rockies near Mt. Elbert. A storm blew in. "I desperately wanted to catch a fish," says Stowell, now president of the Adventure Travel Trade Association in Seattle. "But the storm hit with absolute fury, and my parents said, 'Hey, we've got to get out of here.'

"I didn't want to go. There was something on my line. The thunder was booming, lightning flashing. I reeled in, and it was my first trout. Then it started hailing, and we ran for our camper, dove inside completely drenched, and watched as the storm raged. It was great!"

Then there was the time my dad overfilled the Coleman stove at our campsite in California's Kings Canyon National Park. A grill covered with bacon grease exploded like a mortar round, setting the canvas tent, some towels, and a couple of small trees aflame. (If only we could prevent forest fires, as the Smokey Bear sign near the park's entrance said, this campground was in trouble.) We emerged from the inferno with a great souvenir--the vacation memory.

"Some of the best memories families have are of how they managed to live in nature," says William Doherty, a professor of family studies at the University of Minnesota. "You have to improvise. That's the great thing about nature--you can't preprogram it."

But as the American vacation becomes an endangered species, fewer and fewer kids today have the chance to experience the unprogrammed outdoors.

Family vacations are down 28 percent overall since the 1970s. While two weeks' vacation was the norm in the '60s, only 14 percent of workers take off two weeks or more these days, according to a Harris survey. The average vacation has shrunk to a long weekend. It's not that people are less interested in the natural world. But in today's downsized, BlackBerry-jangling, layoff-prone workplace, increasing numbers of Americans feel they simply can't, or shouldn't, take the time off.

That's a loss for families and the environment. Shared adventure brings families together, thanks to the adhesive properties of the outdoor vacation experience: a time when distractions are nil, new sensory data are intense, and teamwork is required in between sibling battles. "If families are camping or hiking, the members are abandoning their daily routine and roles, discovering new skills, or relying on each other in very different ways," says Vicki Panaccione, a psychologist and founder of the Better Parenting Institute. "There is more need to pitch in together or stay closer or point out new discoveries to each other."

The natural world provides a flash of novelty--thieving blue jays, stars missing from urban skies, or the languid drift of river currents. Ellen Wein, a public-relations professional in Pittsburgh, recalls frequent paddling excursions on the St. Croix River in Wisconsin with her father. "It was so lush and green, no matter where you looked," she says. "We'd see squirrels, lots of birds, and elaborate beaver dams. This wasn't just in cartoons. This was the real thing."

As recently as the 1970s, the family vacation was a thriving tradition. My family joined millions of others in crammed station wagons on guiltless two-week road trips fueled by 40-cent burgers and out-of-state license plate counting. More often than not, we called in at that budget hotelier to the stars (the astronomical variety), the National Park Service.

Unfortunately, the two-week road trip has gone the way of the 40-cent burger. Gillean Smith, a marketing consultant in Trinity, North Carolina, and the mother of two boys, has only a week a year to shoehorn in her family's vacation. This means trips closer to home--like a Carolina beach. "The amount of work makes it challenging to get away sometimes," she says. "But the time collecting shells on the beach with my sons is true one-on-one time. I know it's an emotional detriment to my family if we don't have regular vacations."

Even kids today are too busy for vacations. Children are so overscheduled, they have no time to wander, wonder, or entertain themselves, says Doherty, the Minnesota professor. He cites a family he knows who canceled their summer vacation because the daughter had a soccer game. "What will create better memories for those children, soccer or family time?" he asks. "We need to make vacations sacred, something that nothing short of a hospital stay will take away."

UNLIKE THE UNITED STATES, 137 nations (including all our industrial peers) guarantee holiday time with minimum-paid-leave laws, or legally mandated vacations. Australians get four weeks, Brazilians five, and Europeans as many as six weeks minimum. Even the famously workaholic Japanese have a two-week vacation guaranteed by law.

Since the United States has no minimum-paid-leave statute, vacation time is left to the whim of employers. It's no surprise, then, that vacations are vanishing in the benefits-slashing era, along with pensions and health plans. Some 31 percent of low-income workers receive no vacation leave at all, according to "No-Vacation Nation," a 2007 study by the Center for Economic Policy Research. Among the dwindling numbers of those who do get paid time off, more and more cut their vacation short or don't take one at all, fearing that any absence in a volatile job market might lead to getting the ax. The legacy of decades of leveraged buyouts and mergers, of Wall Street bidding up stocks when layoffs are announced, is that fewer workers have to do more in less time, making it harder to get away.

The lack of leisure time takes a major toll on adults; according to a study by psychologists at the State Univeristy of New York at Oswego, an annual vacation can cut the risk of heart attack in men by 32 percent. And it deprives kids of their best shot at forming a lifelong connection to the natural world.

Standing by the South Fork of the Kings River, I used to marvel at the ceaselessly surging waters: "How can it keep coming?" I'd ask my dad. (My mother would take home little jars of river water as souvenirs, labeling each by the year.) "How can that huge tree grow out of a tiny crack in the cliff?" Out of such musings come further ones--like the idea that all we need to take a stand in this world is a tiny foothold.

In an age when some kids are more likely to text their parents than talk to them, vacations can make families so tight you'd think they knew each other. The active ingredient is time, the most precious of all natural resources, the fastener of all relationships.

"You're sharing the same space for extended periods," says Doherty. "That's unique in family time." But extended family time is in short supply. In the 1970s, four out of five visitors to Yosemite National Park stayed overnight. Now only one in five do. Overnight stays at national parks dropped 20 percent from 1995 to 2005.

"Without time, a lot of children aren't exposed to nature the way we were," says Fran Mainella, former director of the National Park Service and now a visiting scholar at Clemson University. In her own case, she says, it was two-week vacations to national parks with her parents that taught her the value of natural resources and led her to join the Park Service. "If you're not outdoors enjoying resources, you're not as apt to protect them," she says.

There are other connections between outdoor activity and the greater good. Noting the link between housebound children and skyrocketing obesity rates, a few policymakers have taken steps to break kids out of their indoor prisons. Connecticut and other states have launched No Child Left Inside programs to get kids and their families into state parks and forests through games that encourage them to try their hand at hiking, fishing, and scavenger hunts. Texas has a similar campaign dubbed Life's Better Outside. Other programs are trying to yank kids from their video game stupor by bringing technology outdoors with games like geocaching.

But none of these efforts gets to the root of the national vacation crisis: the lack of a minimum-paid-leave law, first proposed by a Labor Department committee a mere 70 years ago. The Committee on Vacations With Pay reported in 1936 that it was "shameful" the country did not have a vacation policy and urged the secretary of labor to draft one. That legislation never happened, but we have a historic opportunity to remedy that omission. The grassroots organizations Take Back Your Time (of which I'm a member) and the Work to Live Campaign (which I founded) have proposed the Minimum Leave Protection Act, which would establish a mandatory standard for paid leave modeled on the minimum-wage law. The legislation would guarantee that anyone who works full-time at a job for one year get 15 days off. That would make us as advanced in the vacation department as the citizens of the Solomon Islands, who get three weeks off by law.

Restoring the family vacation through minimum paid leave is a matter of values, says John de Graaf, founder of Take Back Your Time, author of Affluenza, and a filmmaker working on a documentary called The Great Vacation Squeeze. "What's the economy for, anyway?" de Graaf asks. "Is it just about output, or is it about producing rich, vital lives that allow space for family, community, nature, and discovery?"

We've become accustomed in recent years to overvaluing a small sliver of the life experience: production and its yardsticks, money and stuff. Family, friends, travel, and getting out in nature have been relegated to the bottom of the agenda, but not without a price. Remember those brain neurons? It turns out that if we do the same things all the time, they actually stop noticing. Vacations and time in nature make life fresh and memorable. They reveal the life we're designed for, an unprogrammed adventure.