Diane Ackerman on the natural world, the world of human endeavor and connections between the two.

The Estate of Garry Winogrand, courtesy Fraenkel Gallery, San Francisco

WHEN the Warsaw Zoo was bombed during World War II, killing most of the animals, the zookeepers devised a dangerous plan: they decided to use the cages and enclosures to hide more than 300 Jews who were fleeing the Nazis. Their refuge became one of the most successful hide-outs of the war.

After I wrote about this true story in “The Zookeeper’s Wife,” readers shared their outrage with me about the bombing of a zoo, which they regarded almost as a sacrilege. I heard similar outcries in 2003 after the Baghdad Zoo was bombed. We’re used to the killing of enemies, but we reserve a special circle of hell for people who set fire to zoos. It’s the ultimate massacre of the innocents. The animals are silent victims, supposedly beyond our ideas of good and evil.

More than 150 million people a year visit zoos and aquariums in the United States. Why do we flock to them? It’s not just a pleasant outing with family or friends, or to introduce children (whose lives are a cavalcade of animal images) to real animals, though those are still big reasons. I think people are also drawn to a special stripe of innocence they hope to find there.

Though not a natural world by any means, more like a collection of living dioramas, a zoo exists in its own time zone, somewhere between the seasonal sense of animals and our madly ticking watch time. The relatively quiet, parklike setting offers an oasis in the crowded, noisy, stressful, morally ambiguous world where humans tend to congregate. The random gibbering and roaring, cackling and hooting, yowling and grunting strike ancient chords in us, a feral harmony that intrigues and lulls.

Smells create a subtle olfactory landscape that stirs us: from the sweet drops that male elephants dribble from glands near their eyes in mating season to the scent signposts of lions, hyenas and other animals. Just as dancers have body memory, we have wilderness memory.

One recent online survey suggests that more than half of zoo visitors are family groups — but a big proportion, too, are adults with no children. Zoo researchers have found through eavesdropping studies (in which people at several zoos were observed as zoo animals while they were observing the zoo animals) that most visitors talked surprisingly little. Yet they appeared to the observers to feel closer knit as a result of the visit, judging by their body language, as if there were a special bond that crystallized only in the presence of animals.

Zoogoers mainly strolled and enjoyed “exterior gazing.” That sounds like stop-and-go mindfulness — focusing on the lives of other creatures to dispel the usual mind theaters that plague us. A 2009 study by animal scientists in Japan showed that zoo visitors leave with significantly lower blood pressure, and they report feeling less stressed.

That so many of us, hundreds of millions worldwide, visit zoos each year is also a comment on our times and the marginalization of wild animals from our lives. It’s mainly in films and TV documentaries that we see animals in their natural settings, but on the screen they’re dwarfed, flattened, interrupted by commercials, narrated over and not accompanied by the mixed scents of grass, dung and blood; the drone of flies and cicadas; the welling of sweat.

Let’s set aside for the moment the debate about whether zoos are essential arks and educators or cruel wardens of unhappy animals, because arguments on both sides are compelling. For better or worse, zoos are how most people come to know big or exotic animals. Few will ever see wild penguins sledding downhill to sea on their bellies, giant pandas holding bamboo lollipops in China or tree porcupines in the Canadian Rockies, balled up like giant pine cones. Meeting them at the zoo widens a visitor’s view of nature and personalizes it.

Many of the visitors studied by zoo researchers express a deep rapport with at least one animal and concern for the rest of its species, as well as a better idea of how humans fit into the natural world. It’s telling, I think, that they use personal pronouns when they refer to the animals. In one study, inner-city parents said they visited with their children partly to help promote family values and inspire a concern for animals.

Millions of adults talk un-self-consciously with the animals, maybe to be alone with their thoughts or because they can’t find a companion for the trip. For some it may be a way to socialize, identify, empathize with other beings, without the strain of always interacting with people.

What a lonely species we are, searching for signals of life from other galaxies, adopting companion animals, visiting parks and zoos to commune with other beasts. In the process, we discover our shared identity. We flock to zoos for many reasons, not least to shed some of the burden of being human.