Is there a recreational way to teach how ecosystems work? The destructive and wasteful "economies" we're always propping up with bail-outs and interest-rate cuts are man-made, but it's still air, water, soil and sunlight, and the plants and animals they support, that ultimately keep us alive. Our failure to understand natural systems is a kind of cultural illness, but zoos might be a good venue for applying a remedy.

In my first visit there in a couple years, on Thanksgiving weekend, I petted a ray (the fish, dog-like, seemed to enjoy it) and got my first glimpse of seadragons -- fantastic sea-horse relatives that resemble elegantly floating sprigs of seaweed. And I felt my inevitable ambivalence about cooping close human relatives like orangs and gorillas in boxes. But mostly, I wondered how the zoo might help visitors understand how nature uses all its resources, recycling endlessly to keep things in balance.

Of course, this is inherently difficult for zoos: Animals who mixed there as in the wild would dampen revenue by eating each other, for one thing. And while the synthetic flooring, "foliage" and swimming pools that frame most exhibits are easy to maintain, they give scant sense of how, for instance, a forest processes rainwater.

Granted, displays like the one at the tiger exhibit have long noted how habitat destruction threatens animals with extinction. And there's an old monkey-house display that warns of the consequences of bulldozing rainforests for ranches and farms (even though, when I visited, the display's digital lost-acreage ticker -- perhaps exhausted from the effort -- had stopped counting.)

Some newer displays showed more promise. For instance, the aquarium, in collaboration with groups like The Seahorse Project, bore a detailed sign about global overfishing of the oceans and -- rather remarkably -- basically told people not to eat most shrimp (it's harvested unsustainably) and to lobby government for marine parks, to preserve habitat. Meanwhile, the updated polar bear exhibit offered pamphlets pushing ocean-friendly fish consumption; a sign explaining how petrochemicals like PCBs enter the food web and accumulate in predators like polar bears ... and people; and displays about how emissions from our fossil-fuel consumption is dooming polar bears through climate change.

There's a lot more to be done, and schools, of course, must do the lion's share. But in some ways, zoos, as places of fun, can probably instruct more effectively. If delightful sights -- baby elephants wrasslin' each other; penguins torpedoing through the water in the perpetual dark of a simulated Antarctic winter -- can make us empathize with individual species, they ought to be an inroad for teaching about the whole web of life, too. Even today, and even when they emphasize saving species and habitats, zoos seldom say why those things are more than exercises in sentiment, or asthetics. Too seldom do they tell us that the tigers, polar bears and seahorses are canaries in the coal mine -- and that we live in the same mine.